IT is a technique in which cycles of denaturation, annealing with primer, and extension with DNA polymerase, are used to amplify the number of copies of a target DNA sequence by more than 100 times in a few hours. American molecular biologist Kary Mullis developed the techniques of PCR in the 1970s. For his ingenious invention, he was awarded the 1993 Nobel Prize in physiology or medicine.
PCR amplification of DNA is like any DNA replication by DNA polymerase in vivo. (in lving cells) The difference is that PCR produces DNA in a test tube. For a PCR reaction to proceed, four components are necessary: template, primer, deoxyribonecleotides (adenine, thymine, cytosine, guanine) and DNA polymerase. In addition, part of the sequence of the targeted DNA has to be known in order to design the according primers. In the first step, the targeted double stranded DNA is heated to over 194°F (90°C) for denaturation. During this process, two strands of the targeted DNA are separated from each other. Each strand is capable of being a template. The second step is carried out around 122° (50°C). At this lowered temperature, the two primers anneal to their complementary sequence on each template. The DNA polymerase then extends the primer using the provided NUCLEOTIDES. As a result, at the end of each cycle, the numbers of DNA molecules double.
PCR was initially carried out manually in incubators of different temperatures for each step until the extraction of DNA polymerase from thermophilic bacteria. The bacterium Thermus aquaticus was found in Yellow Stone National Park. This bacterium lives in the hot springs at 203°F (95°C). The DNA polymerase from T. aquaticus keeps its activity at above 95°C for many hours. Several additional heat-resistant DNA polymerases have also now been identified.
Sunday, February 28, 2010
DNA Fingerprinting
Genetic, genomic, or DNA fingerprinting is the term applied to a range of techniques that are used to show similarities and dissimilarities between the DNA present in different individuals.
Genetic fingerprinting is an important tool in the arsenal of forensic investigators. Genetic fingerprinting allows for positive identification, not only of body remains, but also of suspects in custody. Genetic fingerprinting can also link suspects to physical evidence.
Sir Alec Jeffreys at the University of Leicester developed DNA fingerprinting in the mid 1980s. The sequence of NUCLEOTIDES in DNA is similar to a fingerprint, in that it is unique to each person. DNA fingerprinting is used for identifying people, studying populations, and forensic investigations.
Genetic fingerprinting is an important tool in the arsenal of forensic investigators. Genetic fingerprinting allows for positive identification, not only of body remains, but also of suspects in custody. Genetic fingerprinting can also link suspects to physical evidence.
Sir Alec Jeffreys at the University of Leicester developed DNA fingerprinting in the mid 1980s. The sequence of NUCLEOTIDES in DNA is similar to a fingerprint, in that it is unique to each person. DNA fingerprinting is used for identifying people, studying populations, and forensic investigations.
Recombinant DNA
Deoxyribonucleic acid (DNA) is the information blueprint that exists in most living organisms. Some viruses instead contain ribonucleic acid (RNA). Even these viruses require the production of DNA at some stage of their replication.
DNA from different organisms of the same species combines together naturally to yield an organism that has traits from both parent organisms. There is also evidence accumulating that DNA transfer between different species may be a natural process. However, much interspecies mixing of DNA is the result of deliberate experimental manipulations.
A crucial process of these manipulations is the preparation of recombinant DNA. Recombinant DNA is DNA from different organisms that have been chemically bonded together to form a single DNA. The recombinant DNA can be interpreted by the various enzymes of prokaryotic or eukaryotic cells, so that the genes contained in the recombinant DNA can be expressed and the protein products produced.
The recombination can involve the DNA from two eukaryotic organisms, two prokaryotic organisms, or between an eukaryote and a prokaryote. An example of the latter is the production of human insulin by the bacterium E .COLI, which has been achieved by splicing the gene for insulin into the E. coli genome such that the insulin gene is expressed and the protein product formed.
DNA from different organisms of the same species combines together naturally to yield an organism that has traits from both parent organisms. There is also evidence accumulating that DNA transfer between different species may be a natural process. However, much interspecies mixing of DNA is the result of deliberate experimental manipulations.
A crucial process of these manipulations is the preparation of recombinant DNA. Recombinant DNA is DNA from different organisms that have been chemically bonded together to form a single DNA. The recombinant DNA can be interpreted by the various enzymes of prokaryotic or eukaryotic cells, so that the genes contained in the recombinant DNA can be expressed and the protein products produced.
The recombination can involve the DNA from two eukaryotic organisms, two prokaryotic organisms, or between an eukaryote and a prokaryote. An example of the latter is the production of human insulin by the bacterium E .COLI, which has been achieved by splicing the gene for insulin into the E. coli genome such that the insulin gene is expressed and the protein product formed.
Molecular Biology
Molecular biology is an interdisciplinary approach to understanding biological functions and regulation at the level of molecules such as nucleic acids, proteins, and carbohydrates Following the rapid advances in biological science brought about by the development and advancement of the Watson-Crick model of DNA (deoxyribonucleic acid) during the 1950s and 1960s, molecular biologists studied gene structure and function in increasing detail. In addition to advances in understanding genetic machinery and its regulation, molecular biologists continue to make fundamental and powerful discoveries regarding the structure and function of cells and of the mechanisms of genetic transmission. The continued study of these processes by molecular biologists and the advancement of molecular biological techniques requires integration of knowledge derived from physics, chemistry, mathematics, genetics, biochemistry, cell biology and other scientific fields.
Molecular biology also involves organic chemistry, physics , and biophysical chemistry as it deals with the physicochemical structure of macromolecules (nucleic acids, proteins, lipids, and carbohydrates) and their interactions. Genetic materials including DNA in most of the living forms orRNA (ribonucleic acid) in all plant viruses and in some animal viruses remain the subjects of intense study.
In 1945, William Astbury coined the term "molecular biology" referring to the study of the chemical and physical structure of biological macromolecules (large sized molecules). There was and still is a strong belief that all forms of life have uniformity in biological processes. The pioneer findings in prokaryotes (a simple or primitive cell type, e.g., bacteria and blue green alga) are extended to eukaryotes (a complex or well developed cell type, e.g., animal and plant cells).
The complete set of instructions for making an organism (i.e., the complete set of genes) is called its genome. It contains the master blueprint for all cellular structures and activities for the lifetime of the cell or organism. The human genome consists of tightly coiled threads of deoxyribonucleic acid (DNA) and associated protein molecules organized into structures called chromosomes. In humans, as in other higher organisms, a DNA molecule consists of two strands that wrap around each other to resemble a twisted ladder whose sides, made of sugar and phosphate molecules, are connected by rungs of nitrogen-containing chemicals called bases. Each strand is a linear arrangement of repeating similar units called nucleotides, which are each composed of one sugar, one phosphate, and a nitrogenous base. Four different bases are present in DNA adenine (A), thymine (T), cytosine (C), and guanine (G). The particular order of the bases arranged along the sugar-phosphate backbone is called the DNA sequence; the sequence specifies the exact genetic instructions required to create a particular organism with its own unique traits.
Each time a cell divides into two daughter cells, its full genome is duplicated; for humans and other complex organisms, this duplication occurs in the nucleus. During cell division the DNA molecule unwinds and the weak bonds between the base pairs break, allowing the strands to separate. Each strand directs the synthesis of a complementary new strand, with free nucleotides matching up with their complementary bases on each of the separated strands. Strict base-pairing rules are adhered to. Adenine will pair only with thymine (an A-T pair) and cytosine with guanine (a C-G pair). Each daughter cell receives one old and one new DNA strand. The cells adherence to these base-pairing rules ensures that the new strand is an exact copy of the old one. This minimizes the incidence of errors (mutations) that may greatly affect the resulting organism or its offspring.
Each DNA molecule contains many genes, the basic physical and functional units of heredity. A gene is a specific sequence of nucleotide bases, whose sequences carry the information required for constructing proteins, which provide the structural components of cells and tissues as well as enzymes for essential biochemical reactions.
The central dogma of molecular biology is that DNA is copied to make mRNA (messenger RNA) and mRNA is used as the template to make proteins. Formation of RNA is called transcription and formation of protein is called translation. Transcription and translation processes are regulated at various stages and the regulation steps are unique to prokaryotes and eukaryotes. DNA regulation determines what type and amount of mRNA should be transcribed, and this subsequently determines the type and amount of protein. This process is the bottom line for growth and morphogenesis.
Molecular biology also involves organic chemistry, physics , and biophysical chemistry as it deals with the physicochemical structure of macromolecules (nucleic acids, proteins, lipids, and carbohydrates) and their interactions. Genetic materials including DNA in most of the living forms orRNA (ribonucleic acid) in all plant viruses and in some animal viruses remain the subjects of intense study.
In 1945, William Astbury coined the term "molecular biology" referring to the study of the chemical and physical structure of biological macromolecules (large sized molecules). There was and still is a strong belief that all forms of life have uniformity in biological processes. The pioneer findings in prokaryotes (a simple or primitive cell type, e.g., bacteria and blue green alga) are extended to eukaryotes (a complex or well developed cell type, e.g., animal and plant cells).
The complete set of instructions for making an organism (i.e., the complete set of genes) is called its genome. It contains the master blueprint for all cellular structures and activities for the lifetime of the cell or organism. The human genome consists of tightly coiled threads of deoxyribonucleic acid (DNA) and associated protein molecules organized into structures called chromosomes. In humans, as in other higher organisms, a DNA molecule consists of two strands that wrap around each other to resemble a twisted ladder whose sides, made of sugar and phosphate molecules, are connected by rungs of nitrogen-containing chemicals called bases. Each strand is a linear arrangement of repeating similar units called nucleotides, which are each composed of one sugar, one phosphate, and a nitrogenous base. Four different bases are present in DNA adenine (A), thymine (T), cytosine (C), and guanine (G). The particular order of the bases arranged along the sugar-phosphate backbone is called the DNA sequence; the sequence specifies the exact genetic instructions required to create a particular organism with its own unique traits.
Each time a cell divides into two daughter cells, its full genome is duplicated; for humans and other complex organisms, this duplication occurs in the nucleus. During cell division the DNA molecule unwinds and the weak bonds between the base pairs break, allowing the strands to separate. Each strand directs the synthesis of a complementary new strand, with free nucleotides matching up with their complementary bases on each of the separated strands. Strict base-pairing rules are adhered to. Adenine will pair only with thymine (an A-T pair) and cytosine with guanine (a C-G pair). Each daughter cell receives one old and one new DNA strand. The cells adherence to these base-pairing rules ensures that the new strand is an exact copy of the old one. This minimizes the incidence of errors (mutations) that may greatly affect the resulting organism or its offspring.
Each DNA molecule contains many genes, the basic physical and functional units of heredity. A gene is a specific sequence of nucleotide bases, whose sequences carry the information required for constructing proteins, which provide the structural components of cells and tissues as well as enzymes for essential biochemical reactions.
The central dogma of molecular biology is that DNA is copied to make mRNA (messenger RNA) and mRNA is used as the template to make proteins. Formation of RNA is called transcription and formation of protein is called translation. Transcription and translation processes are regulated at various stages and the regulation steps are unique to prokaryotes and eukaryotes. DNA regulation determines what type and amount of mRNA should be transcribed, and this subsequently determines the type and amount of protein. This process is the bottom line for growth and morphogenesis.
DNA Microarray Technology
An array is an orderly arrangement of samples where matching of known and unknown DNA samples is done based on base pairing rules. An array experiment makes use of common assay systems such as microplates or standard blotting membranes. The sample spot sizes are typically less than 200 microns in diameter usually contain thousands of spots.
Thousands of spotted samples known as probes (with known identity) are immobilized on a solid support (a microscope glass slides or silicon chips or nylon membrane). The spots can be DNA, cDNA, or oligonucleotides. These are used to determine complementary binding of the unknown sequences thus allowing parallel analysis for gene expression and gene discovery. An experiment with a single DNA chip can provide information on thousands of genes simultaneously. An orderly arrangement of the probes on the support is important as the location of each spot on the array is used for the identification of a gene.
Types of Microarrays:
Depending upon the kind of immobilized sample used construct arrays and the information fetched, the Microarray experiments can be categorized in three ways:
1. Microarray expression analysis: In this experimental setup, the cDNA derived from the mRNA of known genes is immobilized. The sample has genes from both the normal as well as the diseased tissues. Spots with more more intensity are obtained for diseased tissue gene if the gene is over expressed in the diseased condition. This expression pattern is then compared to the expression pattern of a gene responsible for a disease.
2. Microarray for mutation analysis: For this analysis, the researchers use gDNA. The genes might differ from each other by as less as a single nucleotide base. A single base difference between two sequences is known as Single Nucleotide Polymorphism (SNP) and detecting them is known as SNP detection
3. Comparative Genomic Hybridization: It is used for the identification in the increase or decrease of the important chromosomal fragments harboring genes involved in a disease.
Applications of Microarrays:
Gene discovery: DNA Microarray technology helps in the identification of new genes, know about their functioning and expression levels under different conditions.
Disease diagnosis: DNA Microarray technology helps researchers learn more about different diseases such as heart diseases, mental illness, infectious disease and especially the study of cancer. Until recently, different types of cancer have been classified on the basis of the organs in which the tumors develop. Now, with the evolution of microarray technology, it will be possible for the researchers to further classify the types of cancer on the basis of the patterns of gene activity in the tumor cells. This will tremendously help the pharmaceutical community to develop more effective drugs as the treatment strategies will be targeted directly to the specific type of cancer.
Drug discovery: Microarray technology has extensive application in Pharmacogenomics.Pharmacogenomics is the study of correlations between therapeutic responses to drugs and the genetic profiles of the patients. Comparative analysis of the genes from a diseased and a normal cell will help the identification of the biochemical constitution of the proteins synthesized by the diseased genes. The researchers can use this information to synthesize drugs which combat with these proteins and reduce their effect.
Toxicological research: Microarray technology provides a robust platform for the research of the impact of toxins on the cells and their passing on to the progeny. Toxicogenomics establishes correlation between responses to toxicants and the changes in the genetic profiles of the cells exposed to such toxicants.
Thousands of spotted samples known as probes (with known identity) are immobilized on a solid support (a microscope glass slides or silicon chips or nylon membrane). The spots can be DNA, cDNA, or oligonucleotides. These are used to determine complementary binding of the unknown sequences thus allowing parallel analysis for gene expression and gene discovery. An experiment with a single DNA chip can provide information on thousands of genes simultaneously. An orderly arrangement of the probes on the support is important as the location of each spot on the array is used for the identification of a gene.
Types of Microarrays:
Depending upon the kind of immobilized sample used construct arrays and the information fetched, the Microarray experiments can be categorized in three ways:
1. Microarray expression analysis: In this experimental setup, the cDNA derived from the mRNA of known genes is immobilized. The sample has genes from both the normal as well as the diseased tissues. Spots with more more intensity are obtained for diseased tissue gene if the gene is over expressed in the diseased condition. This expression pattern is then compared to the expression pattern of a gene responsible for a disease.
2. Microarray for mutation analysis: For this analysis, the researchers use gDNA. The genes might differ from each other by as less as a single nucleotide base. A single base difference between two sequences is known as Single Nucleotide Polymorphism (SNP) and detecting them is known as SNP detection
3. Comparative Genomic Hybridization: It is used for the identification in the increase or decrease of the important chromosomal fragments harboring genes involved in a disease.
Applications of Microarrays:
Gene discovery: DNA Microarray technology helps in the identification of new genes, know about their functioning and expression levels under different conditions.
Disease diagnosis: DNA Microarray technology helps researchers learn more about different diseases such as heart diseases, mental illness, infectious disease and especially the study of cancer. Until recently, different types of cancer have been classified on the basis of the organs in which the tumors develop. Now, with the evolution of microarray technology, it will be possible for the researchers to further classify the types of cancer on the basis of the patterns of gene activity in the tumor cells. This will tremendously help the pharmaceutical community to develop more effective drugs as the treatment strategies will be targeted directly to the specific type of cancer.
Drug discovery: Microarray technology has extensive application in Pharmacogenomics.Pharmacogenomics is the study of correlations between therapeutic responses to drugs and the genetic profiles of the patients. Comparative analysis of the genes from a diseased and a normal cell will help the identification of the biochemical constitution of the proteins synthesized by the diseased genes. The researchers can use this information to synthesize drugs which combat with these proteins and reduce their effect.
Toxicological research: Microarray technology provides a robust platform for the research of the impact of toxins on the cells and their passing on to the progeny. Toxicogenomics establishes correlation between responses to toxicants and the changes in the genetic profiles of the cells exposed to such toxicants.
DNA Replication – The Replisome
The replisome is a complex molecular machine that carries out replication of DNA. It is comprised of a number of subcomponents, each performing a specific function during the process of replication. Helicase is an enzyme which breaks the hydrogen bonds between the two strands of DNA, thus separating the strands ahead of DNA synthesis. As helicase unwinds the double helix, it induces the formation of supercoils in other areas of the DNA.
Gyrase relaxes and undoes the supercoiling which has been caused by the helicase by cutting the DNA strands, allowing it to rotate and release the supercoil, and then rejoining the strands. Gyrase is most commonly located upstreak of the replication fork -- where the supercoils are being formed.
Primase adds complementary RNA primers to a DNA strand to begin Okazaki fragments. In addition, because DNA Polymerae can only continue (but not begin) a strand, Primase begins the leading strand as well.
DNA polymerase III is comprised of two catalytic cores -- one for replication of the leading strand and one for the lagging strand. DNA polemerase III, however, cannot stay on the DNA strand long enough to efficiently replicate a daughter strand. Hence, DNA polymerase III stays on the strands via a dimer beta clamp which contains three subunits that come together to enclose the strand -- ensuring that DNA polymerase III will remain on the strand for a few thousand nucleotides as opposed to a few hundred.
DNA polymerase I removes the RNA primers set by Primase and completes the Okazaki fragments. Because there is such a small gap remaining after the action of DNA polymerase I has continued the strand of the Okazaki fragment, ligase is required to fill in the gap. The two ends of the Okazaki fragments are subsequently connected by covalent bonds.
Single-strand binding proteins bind to the exposed bases in an effort to counteract their instability and prevent the single-strand DNA from hydrogen-bonding to itself to form dangerous hairpin structures.
DNA polymerases contain a ‘proofreading’ mechanism, commonly referred to as ‘exonuclease activity’. This removes nucleotides that have been mistakenly added.
DNA Replication – Signature of Design
DNA Replication stands as a fundamental challenge to those who seek to hold to a Darwinian worldview. As the process by which biological information is copied and passed on to succeeding generations, the mechanism is fundamental to the process of self-replication of cells. Yet self-replication of cells is necessary for the operation of any selective process such as natural selection. Thus, to attempt to explain the immense sophistication of this mechanism with reference to natural selection requires one to presuppose the existence of the very thing they wish to explain. Because of its extremely sophisticated nature, most biochemists previously reckoned that the system arose once, prior to the origin of the last universal common ancestor. In addition, many biochemists have long regarded the close functional similarity of DNA replication observed in all life as evidence for the single origin of DNA replication. Yet in 1999 researchers from the National Institutes of Health demonstrated that the core enzymes involved in the DNA replication machinery of bacteria and archae/eukaryotes (the two major trunks of the evolutionary tree of life) did not in fact share a common evolutionary origin. It thus appears as if two identical DNA replication systems have emerged independently in bacteria and archae -- after these two evolutionary lineages supposedly diverged from the last universal common ancestor.
It is phenomenal to think that this engineering marvel evolved a single time, let alone twice. There exists no obvious reason for DNA replication to take place by a semiconservative, RNA primer-dependent, bidirectional mechanism that depends on leading and lagging strands to produce DNA daughter molecules. Even if DNA replication could have evolved independently on two separate occasions, it is reasonable to expect that fundamentally different mechanisms would emerge for bacteria and the archae/eukaryotes given their idiosyncrasies. But, they did not.
Gyrase relaxes and undoes the supercoiling which has been caused by the helicase by cutting the DNA strands, allowing it to rotate and release the supercoil, and then rejoining the strands. Gyrase is most commonly located upstreak of the replication fork -- where the supercoils are being formed.
Primase adds complementary RNA primers to a DNA strand to begin Okazaki fragments. In addition, because DNA Polymerae can only continue (but not begin) a strand, Primase begins the leading strand as well.
DNA polymerase III is comprised of two catalytic cores -- one for replication of the leading strand and one for the lagging strand. DNA polemerase III, however, cannot stay on the DNA strand long enough to efficiently replicate a daughter strand. Hence, DNA polymerase III stays on the strands via a dimer beta clamp which contains three subunits that come together to enclose the strand -- ensuring that DNA polymerase III will remain on the strand for a few thousand nucleotides as opposed to a few hundred.
DNA polymerase I removes the RNA primers set by Primase and completes the Okazaki fragments. Because there is such a small gap remaining after the action of DNA polymerase I has continued the strand of the Okazaki fragment, ligase is required to fill in the gap. The two ends of the Okazaki fragments are subsequently connected by covalent bonds.
Single-strand binding proteins bind to the exposed bases in an effort to counteract their instability and prevent the single-strand DNA from hydrogen-bonding to itself to form dangerous hairpin structures.
DNA polymerases contain a ‘proofreading’ mechanism, commonly referred to as ‘exonuclease activity’. This removes nucleotides that have been mistakenly added.
DNA Replication – Signature of Design
DNA Replication stands as a fundamental challenge to those who seek to hold to a Darwinian worldview. As the process by which biological information is copied and passed on to succeeding generations, the mechanism is fundamental to the process of self-replication of cells. Yet self-replication of cells is necessary for the operation of any selective process such as natural selection. Thus, to attempt to explain the immense sophistication of this mechanism with reference to natural selection requires one to presuppose the existence of the very thing they wish to explain. Because of its extremely sophisticated nature, most biochemists previously reckoned that the system arose once, prior to the origin of the last universal common ancestor. In addition, many biochemists have long regarded the close functional similarity of DNA replication observed in all life as evidence for the single origin of DNA replication. Yet in 1999 researchers from the National Institutes of Health demonstrated that the core enzymes involved in the DNA replication machinery of bacteria and archae/eukaryotes (the two major trunks of the evolutionary tree of life) did not in fact share a common evolutionary origin. It thus appears as if two identical DNA replication systems have emerged independently in bacteria and archae -- after these two evolutionary lineages supposedly diverged from the last universal common ancestor.
It is phenomenal to think that this engineering marvel evolved a single time, let alone twice. There exists no obvious reason for DNA replication to take place by a semiconservative, RNA primer-dependent, bidirectional mechanism that depends on leading and lagging strands to produce DNA daughter molecules. Even if DNA replication could have evolved independently on two separate occasions, it is reasonable to expect that fundamentally different mechanisms would emerge for bacteria and the archae/eukaryotes given their idiosyncrasies. But, they did not.
Therapeutic Cloning
Somatic cell nuclear transfer can also be used to create a clonal embryo. The most likely scenario for this is to produce embryos for use in research, particularly stem cell research. This process is also called "research cloning" or "therapeutic cloning."
Therapeutic cloning is the production of human embryos for use in research. The goal of this process is not to create cloned human beings, but rather to harvest stem cells that can be used to study human development and to treat disease. Stem cells are important to biomedical researchers because they can be used to generate virtually any type of specialized cell in the human body. Stem cells are extracted from the egg after it has divided for 5 days. The egg at this stage of development is called a blastocyst. Many researchers hope that one day stem cells can be used to serve as replacement cells to treat heart disease, Alzheimer's, cancer, and other diseases.
Therapeutic cloning is the production of human embryos for use in research. The goal of this process is not to create cloned human beings, but rather to harvest stem cells that can be used to study human development and to treat disease. Stem cells are important to biomedical researchers because they can be used to generate virtually any type of specialized cell in the human body. Stem cells are extracted from the egg after it has divided for 5 days. The egg at this stage of development is called a blastocyst. Many researchers hope that one day stem cells can be used to serve as replacement cells to treat heart disease, Alzheimer's, cancer, and other diseases.
Hybrid & Chimeras
Hybrid animals are created when gametes (reproductive cells) from different species join to form a single embryo. A mule, for example, is the offspring of a female horse and a male donkey. Every cell in the body of hybrids contains genetic material from both parents.
Chimeras, named after creatures from Greek mythology, are created artificially by combining genetic material from different species into a single embryo. The adult animals that develop have different populations of cells that reflect different contributions from the species from which they were produced. Scientists have created the geep, for example, by combining genetic material from both a goat and a sheep.
Partially human hybrid embryos have been created by fusing human cells and animal eggs, and partially human chimeric embryos have been created by injecting human embryonic stem cells into animal embryos. Most scientists want to produce such embryos only for research, and oppose experiments that would allow human-animal chimeras to be brought to term.
The prospect of human-animal chimeras troubles many people and raises troubling questions about their moral and legal status. Would a human-animal chimera have human rights? Could it be patented and owned? What if it were 99.9% human and 0.1% chimpanzee?
Chimeras, named after creatures from Greek mythology, are created artificially by combining genetic material from different species into a single embryo. The adult animals that develop have different populations of cells that reflect different contributions from the species from which they were produced. Scientists have created the geep, for example, by combining genetic material from both a goat and a sheep.
Partially human hybrid embryos have been created by fusing human cells and animal eggs, and partially human chimeric embryos have been created by injecting human embryonic stem cells into animal embryos. Most scientists want to produce such embryos only for research, and oppose experiments that would allow human-animal chimeras to be brought to term.
The prospect of human-animal chimeras troubles many people and raises troubling questions about their moral and legal status. Would a human-animal chimera have human rights? Could it be patented and owned? What if it were 99.9% human and 0.1% chimpanzee?
SIGNAL TRANSDUCTION GENE THERAPY (STGT)
Signal transduction refers to the most common method of regulation of complex cell activity. It involves an external signal molecule (ligand) being bound by a specific cell's membrane receptor. The receptor, in turn triggers changes in the internal command system of the cell causing it to undertake a new activity so long as the ligand is present. A powerful new therapy using STGT is being developed whereby part of the genome of a common cold virus is replaced with:
1. A gene or genes that make a therapeutic chemical (e.g. hormone, cytokine etc.) and
2. A gene or genes that regulates the production of the therapeutic genes and that is itself "switched on" by a chemical that can be given to the patient.
In this procedure the patient is infected by the modified virus. The modified viral DNA then remains in the patient's cells. The therapy gene remain inactive until the "triggering" substance was given externally. The amount of triggering substance would determine the degree to which the therapy gene was turned on (like a dimmer switch).
1. A gene or genes that make a therapeutic chemical (e.g. hormone, cytokine etc.) and
2. A gene or genes that regulates the production of the therapeutic genes and that is itself "switched on" by a chemical that can be given to the patient.
In this procedure the patient is infected by the modified virus. The modified viral DNA then remains in the patient's cells. The therapy gene remain inactive until the "triggering" substance was given externally. The amount of triggering substance would determine the degree to which the therapy gene was turned on (like a dimmer switch).
Genomic DNAs
Genomic DNAs are unconnected from over 100 disparate manlike and fetal practice tissues, fallible pathological and tumor tissues, creep, rat, monkey, and lay tissues. Our genomic DNAs are provided prepared to use for SNP analysis, DNA methylation psychotherapy, reduplicate periodical variation (CNV) or comparative genomic hybridization (CGH) psychotherapy, Southern Blotting, and PCR. BioChain offers near any genomic DNAs from weak, pussyfoot, rat, monkey, opposite animals, and position tissues. Effort genomic DNAs from BioChain present prevent you invaluable search dimension to forthwith distinguish genes of relate; no longer give you requirement to adopt tissues and insulate genomic DNA by yourself.
The chronicle of DNA search is a tale of uncomplaining researchers busy day after day on myriad tiny problems. It is a tale of myriad answers assemblage at measure into profound insights. This is what happened with the Human Genome Projection.
The theme the HGP set out to answer was: What are all the genes in a imperfect being? The geneticists working on the Propel already knew a lot. They knew that genes use by manufacturing proteins. They knew that genes do this indirectly: Enzymes in the radiophone karyon move and unzip tune of a DNA multiply helix and make a assets of the DNA, a point sequence, into molecules of traveler RNA. The traveler RNA exits the karyon and carries the factor's cypher to cadre parts in the cytoplasm, to undeviating protein make. Eventually, the geneticists knew that humans change around 100,000 different types of proteins in their bodies. So researchers foreseen the HGP to move period, and to any Project geneticists devised new, speedier techniques for decipherment DNA. A lot sooner than expected, the healthy hominine genome was identified. And there weren't 100,000 genes-there were exclusive near 30,000! Or maybe only 25,000! A undignified conundrum: How do 100,000 proteins get manufactured by exclusive 25,000 genes?
Before the Hominine Genome Plan got started, something added had grow to illuminated: After a stuff of courier RNA is derived from a cistron, and before the traveler RNA leaves the room karyon, it gets "altered." Molecules titled spliceosomes cut the RNA message into fragments, take some of the fragments, and junction the put posterior unitedly again. The spliced message is what actually passes out of the cadre organelle into the cytoplasm, and gets translated into a accelerator.
But the spliced message isn't ever the unvaried. The set of fragments that get spliced unitedly can dissent. So that secondary proteins conclusion from the equal traveller RNA, and thence from the aforementioned sequence. So this is how 25,000 genes micturate 100,000 proteins.
How did this intricate group germinate? Whatever biologists believe the best active, reaction exploit molecules of lifespan were RNA's, patch others reckon they were proteins. Intriguingly, spliceosomes love few of both. Could deciding splicing be adjacent to the early molecules of invigoration? When we analyse this editing of RNA, are we perception far game into being's beginnings, virtuous as we see far support into the beginnings of the macrocosm when we canvass the oldest palish
The chronicle of DNA search is a tale of uncomplaining researchers busy day after day on myriad tiny problems. It is a tale of myriad answers assemblage at measure into profound insights. This is what happened with the Human Genome Projection.
The theme the HGP set out to answer was: What are all the genes in a imperfect being? The geneticists working on the Propel already knew a lot. They knew that genes use by manufacturing proteins. They knew that genes do this indirectly: Enzymes in the radiophone karyon move and unzip tune of a DNA multiply helix and make a assets of the DNA, a point sequence, into molecules of traveler RNA. The traveler RNA exits the karyon and carries the factor's cypher to cadre parts in the cytoplasm, to undeviating protein make. Eventually, the geneticists knew that humans change around 100,000 different types of proteins in their bodies. So researchers foreseen the HGP to move period, and to any Project geneticists devised new, speedier techniques for decipherment DNA. A lot sooner than expected, the healthy hominine genome was identified. And there weren't 100,000 genes-there were exclusive near 30,000! Or maybe only 25,000! A undignified conundrum: How do 100,000 proteins get manufactured by exclusive 25,000 genes?
Before the Hominine Genome Plan got started, something added had grow to illuminated: After a stuff of courier RNA is derived from a cistron, and before the traveler RNA leaves the room karyon, it gets "altered." Molecules titled spliceosomes cut the RNA message into fragments, take some of the fragments, and junction the put posterior unitedly again. The spliced message is what actually passes out of the cadre organelle into the cytoplasm, and gets translated into a accelerator.
But the spliced message isn't ever the unvaried. The set of fragments that get spliced unitedly can dissent. So that secondary proteins conclusion from the equal traveller RNA, and thence from the aforementioned sequence. So this is how 25,000 genes micturate 100,000 proteins.
How did this intricate group germinate? Whatever biologists believe the best active, reaction exploit molecules of lifespan were RNA's, patch others reckon they were proteins. Intriguingly, spliceosomes love few of both. Could deciding splicing be adjacent to the early molecules of invigoration? When we analyse this editing of RNA, are we perception far game into being's beginnings, virtuous as we see far support into the beginnings of the macrocosm when we canvass the oldest palish
Saturday, February 27, 2010
DNA Double Helix
DNA is a normally double stranded macromolecule. Two polynucleotide chains, held together by weak thermodynamic forces, form a DNA molecule.
Features of the DNA Double Helix
* Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral
* The two polynucleotide chains run in opposite directions
* The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a sprial staircase
* The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase.
DNA Helix Axis
The helix axis is most apparent from a view directly down the axis. The sugar-phosphate backbone is on the outside of the helix where the polar phosphate groups (red and yellow atoms) can interact with the polar environment. The nitrogen (blue atoms) containing bases are inside, stacking perpendicular to the helix axis.
Features of the DNA Double Helix
* Two DNA strands form a helical spiral, winding around a helix axis in a right-handed spiral
* The two polynucleotide chains run in opposite directions
* The sugar-phosphate backbones of the two DNA strands wind around the helix axis like the railing of a sprial staircase
* The bases of the individual nucleotides are on the inside of the helix, stacked on top of each other like the steps of a spiral staircase.
DNA Helix Axis
The helix axis is most apparent from a view directly down the axis. The sugar-phosphate backbone is on the outside of the helix where the polar phosphate groups (red and yellow atoms) can interact with the polar environment. The nitrogen (blue atoms) containing bases are inside, stacking perpendicular to the helix axis.
DNA structure
DNA structure shows a variety of forms, both double-stranded and single-stranded. The mechanical properties of DNA, which are directly related to its structure, are a significant problem for cells. Every process which binds or reads DNA is able to use or modify the mechanical properties of DNA for purposes of recognition, packaging and modification. The extreme length (a chromosome may contain a 10 cm long DNA strand), relative rigidity and helical structure of DNA has led to the evolution of histones and of enzymes such as topoisomerases and helicases to manage a cell's DNA. The properties of DNA are closely related to its molecular structure and sequence, particularly the weakness of the hydrogen bonds and electronic interactions that hold strands of DNA together compared to the strength of the bonds within each strand.
Dna Structure
Experimental techniques which can directly measure the mechanical properties of DNA are relatively new, and high-resolution visualization in solution is often difficult. Nevertheless, scientists have uncovered large amount of data on the mechanical properties of this polymer, and the implications of DNA's mechanical properties on cellular processes is a topic of active current research.
The DNA found in many cells can be macroscopic in length - a few centimetres long for each human chromosome. Consequently, cells must compact or "package" DNA to carry it within them. In eukaryotes this is carried by spool-like proteins known as histones, around which DNA winds. It is the further compaction of this DNA-protein complex which produces the well known mitotic eukaryotic chromosomes.
Dna Structure
Experimental techniques which can directly measure the mechanical properties of DNA are relatively new, and high-resolution visualization in solution is often difficult. Nevertheless, scientists have uncovered large amount of data on the mechanical properties of this polymer, and the implications of DNA's mechanical properties on cellular processes is a topic of active current research.
The DNA found in many cells can be macroscopic in length - a few centimetres long for each human chromosome. Consequently, cells must compact or "package" DNA to carry it within them. In eukaryotes this is carried by spool-like proteins known as histones, around which DNA winds. It is the further compaction of this DNA-protein complex which produces the well known mitotic eukaryotic chromosomes.
Genetic testing
Point 1 Genetic testing permits Genetic diagnosis of diseases and vulnerability to a "child, S (genetic father) or a person's sex may determine paternity can be used. Normally, each person has two copies of a gene is one that her mother, one inherited from his father but will be taken. Human genome includes around 20,000 for the trust - is 25,000 genes.
Point 2 Individual gene and gene genetic diseases, genetic disorders that are associated with increasing risk of developing type variation for the possible presence of biochemical tests in the direction of a further level of chromosomes, including genetic testing than to study. Genetic testing identifies changes in chromosomes, genes or proteins. Generally, changes in testing that are associated with inherited disorders is found.
Point 3 A genetic test results confirm a suspected genetic condition or can cross out or to determine a "person of science or beyond is likely to help developing a genetic disorder. Coll several hundred genetic tests are common, and more are being developed.
Point 2 Individual gene and gene genetic diseases, genetic disorders that are associated with increasing risk of developing type variation for the possible presence of biochemical tests in the direction of a further level of chromosomes, including genetic testing than to study. Genetic testing identifies changes in chromosomes, genes or proteins. Generally, changes in testing that are associated with inherited disorders is found.
Point 3 A genetic test results confirm a suspected genetic condition or can cross out or to determine a "person of science or beyond is likely to help developing a genetic disorder. Coll several hundred genetic tests are common, and more are being developed.
Benefits of Genetic genealogy
Genetic genealogy gives the Genealogists, which are to examine or be supplemented means, their results of genealogy with the information, which is caught up over DNA examination. Positive test matches with another individual can:
* you put to positions for further descent research at the disposal
* assistance place ererbtes native country
* firmly discover you living relatives
* validate you existing research
* confirm you or refuse you assumed connections between families
* examine you or disprove you concerning theories sex
* you put to positions for further descent research at the disposal
* assistance place ererbtes native country
* firmly discover you living relatives
* validate you existing research
* confirm you or refuse you assumed connections between families
* examine you or disprove you concerning theories sex
Types of Genetic testing
• Newborn Screening: Newborn screening immediately after birth using genetic disorders that can be treated early in life are identified. Regular testing of children for some genetic disorders and the most widely used is Geprüftmillionen children every year in the United States are examined. Coll kid on the states considered Phenylketonuria (a genetic disorder that causes mental illness, if treatment) and congenital hypothyroidism (thyroid gland disorder of).
• Clinical trials: Clinical trials to determine the status of a specific genetic or chromosome, or hit out is used. In many cases, for genetic diagnosis were confirmed when a certain situation suggested the test was based on physical changes and symptoms. One person at any time during the clinical trials done 'can be, S life, but all the genes or genetic conditions is not available for all. Clinical trial results of a one-man, S. affect health care and disease management can choose.
• carrier testing: carrier testing people, a copy of a gene mutation which, if used to identify existing lift, two copies of a genetic disorder caused. Examination of such individuals a genetic disorder that people in ethnic groups have offered to family history and increased risk of specific genetic conditions. If both parents are tested, "made a pair is available, the risk of a child with a genetic condition S test report.
• Prenatal testing: one for pre-natal testing "to detect changes in the use of embryos, genes or chromosomes before birth is s. Examination of such a genetic or chromosomal disorder, with an increased risk of having a baby has offered to couples. In some cases, a prenatal test 'two, S-uncertainty may reduce or help them decide whether pregnancy terminates. Identify all possible inherited disorders and birth can not fault.
• Preimplantation genetic diagnosis: Genetic testing that the human embryo, before implantation as part of the processes are performing in vitro fertilization.
• East and presymptomatic testing: pre-determined, changes in gene identification and evaluation of presymptomatic forms often used in later life disorders that appear after birth are associated with. These tests are the people, a genetic disorder, with one family member can help, but whatever time you test a feature of the disorder is. Pre-determined test changes, a growing 'human, such as some types of cancer as a genetic basis, the possibility of developing disorders with S can be identified. Example, one person BRCA1, 65% cumulative risk of breast cancer have a change. Can determine whether a Presymptomatic testing person (an iron overload disorder) as developed hemochromatosis is a genetic disorder, no signs or symptoms first appear. Previous results and a specific disorder, presymptomatic testing and treatment in developing decision support available information about an individual's risks can provide.
• Judicial Review: Forensic testing uses DNA sequence identity of any person for the purposes authorized. Unlike the test described above, the use of judicial review that gene mutations are associated with illness is not identified. Testing of such crime or accident victims, to identify or exclude a biological relationship between people Verbrechenverdächtigen or installation means (eg, parenthood) can cross.
• Clinical trials: Clinical trials to determine the status of a specific genetic or chromosome, or hit out is used. In many cases, for genetic diagnosis were confirmed when a certain situation suggested the test was based on physical changes and symptoms. One person at any time during the clinical trials done 'can be, S life, but all the genes or genetic conditions is not available for all. Clinical trial results of a one-man, S. affect health care and disease management can choose.
• carrier testing: carrier testing people, a copy of a gene mutation which, if used to identify existing lift, two copies of a genetic disorder caused. Examination of such individuals a genetic disorder that people in ethnic groups have offered to family history and increased risk of specific genetic conditions. If both parents are tested, "made a pair is available, the risk of a child with a genetic condition S test report.
• Prenatal testing: one for pre-natal testing "to detect changes in the use of embryos, genes or chromosomes before birth is s. Examination of such a genetic or chromosomal disorder, with an increased risk of having a baby has offered to couples. In some cases, a prenatal test 'two, S-uncertainty may reduce or help them decide whether pregnancy terminates. Identify all possible inherited disorders and birth can not fault.
• Preimplantation genetic diagnosis: Genetic testing that the human embryo, before implantation as part of the processes are performing in vitro fertilization.
• East and presymptomatic testing: pre-determined, changes in gene identification and evaluation of presymptomatic forms often used in later life disorders that appear after birth are associated with. These tests are the people, a genetic disorder, with one family member can help, but whatever time you test a feature of the disorder is. Pre-determined test changes, a growing 'human, such as some types of cancer as a genetic basis, the possibility of developing disorders with S can be identified. Example, one person BRCA1, 65% cumulative risk of breast cancer have a change. Can determine whether a Presymptomatic testing person (an iron overload disorder) as developed hemochromatosis is a genetic disorder, no signs or symptoms first appear. Previous results and a specific disorder, presymptomatic testing and treatment in developing decision support available information about an individual's risks can provide.
• Judicial Review: Forensic testing uses DNA sequence identity of any person for the purposes authorized. Unlike the test described above, the use of judicial review that gene mutations are associated with illness is not identified. Testing of such crime or accident victims, to identify or exclude a biological relationship between people Verbrechenverdächtigen or installation means (eg, parenthood) can cross.
Helicases
Helicases are a class of enzymes vital to all living organisms. They are motor proteins that move directionally along a nucleic acid phosphodiester backbone, separating two annealed nucleic acid strands (i.e. DNA, RNA, or RNA-DNA hybrid) using energy derived from ATP hydrolysis.
Many cellular processes (DNA replication, transcription, translation, recombination, DNA repair, ribosome biogenesis) involve the separation of nucleic acid strands. Helicases are often utilized to separate strands of a DNA double helix or a self-annealed RNA molecule using the energy from ATP hydrolysis, a process characterized by the breaking of hydrogen bonds between annealed nucleotide bases. They move incrementally along one nucleic acid strand of the duplex with a directionality and processivity specific to each particular enzyme. There are many helicases (14 confirmed in E. coli, 24 in human cells) resulting from the great variety of processes in which strand separation must be catalyzed.
Helicases adopt different structures and oligomerization states. Whereas DnaB-like helicases unwind DNA as donut shaped hexamers, other enzymes have been shown to be active as monomers or dimers. Studies have shown that helicases may act passively, waiting for uncatalyzed unwinding to take place and then translocating between displaced strands, or can play an active role in catalyzing strand separation using the energy generated in ATP hydrolysis. In the latter case, the helicase acts comparably to an active motor, unwinding and translocating along its substrate as a direct result ATPase activity.. Helicases may process much faster in vivo than in vitro due to the presence of accessory proteins that aid in the destabilization of the fork junction.
Defects in the gene that codes helicase cause Werner syndrome, a disorder characterized by the appearance of premature aging.
Many cellular processes (DNA replication, transcription, translation, recombination, DNA repair, ribosome biogenesis) involve the separation of nucleic acid strands. Helicases are often utilized to separate strands of a DNA double helix or a self-annealed RNA molecule using the energy from ATP hydrolysis, a process characterized by the breaking of hydrogen bonds between annealed nucleotide bases. They move incrementally along one nucleic acid strand of the duplex with a directionality and processivity specific to each particular enzyme. There are many helicases (14 confirmed in E. coli, 24 in human cells) resulting from the great variety of processes in which strand separation must be catalyzed.
Helicases adopt different structures and oligomerization states. Whereas DnaB-like helicases unwind DNA as donut shaped hexamers, other enzymes have been shown to be active as monomers or dimers. Studies have shown that helicases may act passively, waiting for uncatalyzed unwinding to take place and then translocating between displaced strands, or can play an active role in catalyzing strand separation using the energy generated in ATP hydrolysis. In the latter case, the helicase acts comparably to an active motor, unwinding and translocating along its substrate as a direct result ATPase activity.. Helicases may process much faster in vivo than in vitro due to the presence of accessory proteins that aid in the destabilization of the fork junction.
Defects in the gene that codes helicase cause Werner syndrome, a disorder characterized by the appearance of premature aging.
DNA polymerase
A DNA polymerase is an enzyme that catalyzes the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best-known for their role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand. The newly-polymerized molecule is complementary to the template strand and identical to the template's original partner strand.
DNA polymerases use a magnesium ion for catalytic activity.
DNA polymerase can add free nucleotides to only the 3’ end of the newly-forming strand. This results in elongation of the new strand in a 5'-3' direction. No known DNA polymerase is able to begin a new chain (de novo). DNA polymerase can add a nucleotide onto only a preexisting 3'-OH group, and, therefore, needs a primer at which it can add the first nucleotide. Primers consist of RNA and DNA bases with the first two bases always being RNA, and are synthesized by another enzyme called primase. An enzyme known as a helicase is required to unwind DNA from a double-strand structure to a single-strand structure to facilitate replication of each strand consistent with the semiconservative model of DNA replication.
Error correction is a property of some, but not all, DNA polymerases. This process corrects mistakes in newly-synthesized DNA. When an incorrect base pair is recognized, DNA polymerase reverses its direction by one base pair of DNA. The 3'->5' exonuclease activity of the enzyme allows the incorrect base pair to be excised Following base excision, the polymerase can re-insert the correct base and replication can continue.
DNA polymerases use a magnesium ion for catalytic activity.
DNA polymerase can add free nucleotides to only the 3’ end of the newly-forming strand. This results in elongation of the new strand in a 5'-3' direction. No known DNA polymerase is able to begin a new chain (de novo). DNA polymerase can add a nucleotide onto only a preexisting 3'-OH group, and, therefore, needs a primer at which it can add the first nucleotide. Primers consist of RNA and DNA bases with the first two bases always being RNA, and are synthesized by another enzyme called primase. An enzyme known as a helicase is required to unwind DNA from a double-strand structure to a single-strand structure to facilitate replication of each strand consistent with the semiconservative model of DNA replication.
Error correction is a property of some, but not all, DNA polymerases. This process corrects mistakes in newly-synthesized DNA. When an incorrect base pair is recognized, DNA polymerase reverses its direction by one base pair of DNA. The 3'->5' exonuclease activity of the enzyme allows the incorrect base pair to be excised Following base excision, the polymerase can re-insert the correct base and replication can continue.
DNA topoisomerase:
DNA topoisomerase DNA supercoiling changes. Reduction of DNA-DNA topoisomerase. Type of DNA topoisomerase I drop a hair and DNA topoisomerase II-type knife with two teeth. DNA Topoisomerase regulates DNA supercoiling. Help topoisomerase DNA transcription and replication of DNA. And DNA topoisomerase I and DNA topoisomerase II, a DNA topoisomerase DNA topoisomerase III and IV.
DNA topoisomerase: DNA topoisomerase is an enzyme that changes the supercoiling of double DNA. DNA topoisomerase acts for a short cut one or both strands of DNA. DNA topoisomerase type I series of cuts and the level of DNA topoisomerase II knife with two strands of DNA. Coil leave DNA topoisomerase and extends the DNA molecule. DNA topoisomerase helps regulate DNA supercoiling. DNA topoisomerase using DNA replication and transcription. Just as DNA topoisomerase I and DNA topoisomerase II, a DNA topoisomerase DNA topoisomerase III and IV. DNA topoisomerase III may regulate recombination. DNA topoisomerase IV regulates the separation of newly replicated chromosomes.
DNA topoisomerase: DNA topoisomerase is an enzyme that changes the supercoiling of double DNA. DNA topoisomerase acts for a short cut one or both strands of DNA. DNA topoisomerase type I series of cuts and the level of DNA topoisomerase II knife with two strands of DNA. Coil leave DNA topoisomerase and extends the DNA molecule. DNA topoisomerase helps regulate DNA supercoiling. DNA topoisomerase using DNA replication and transcription. Just as DNA topoisomerase I and DNA topoisomerase II, a DNA topoisomerase DNA topoisomerase III and IV. DNA topoisomerase III may regulate recombination. DNA topoisomerase IV regulates the separation of newly replicated chromosomes.
Types of Gene Therapy
Gene therapy
is the insertion of genes into an individual's cells and tissues to treat a disease, and hereditary diseases in which a defective mutant allele is replaced with a functional one. Although the technology is still in its infancy, it has been used with some success. Antisense therapy is not strictly a form of gene therapy, but is a genetically-mediated therapy and is often considered together with other methods.
How does gene therapy work?
In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene. A carrier molecule called a vector must be used to deliver the therapeutic gene to the patient's target cells. Currently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists have tried to take advantage of this capability and manipulate the virus genome to remove disease-causing genes and insert therapeutic genes.
Target cells such as the patient's liver or lung cells are infected with the viral vector. The vector then unloads its genetic material containing the therapeutic human gene into the target cell. The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state.
How is gene therapy being studied in the treatment of cancer?
Researchers are studying several ways to treat cancer using gene therapy. Some approaches target healthy cells to enhance their ability to fight cancer. Other approaches target cancer cells, to destroy them or prevent their growth. Some gene therapy techniques under study are described below. In one approach, researchers replace missing or altered genes with healthy genes.
The types of gene therapy described thus far all have one factor in common: that is, that the tissues being treated are somatic (somatic cells include all the cells of the body, excluding sperm cells and egg cells). In contrast to this is the replacement of defective genes in the germline cells (which contribute to the genetic heritage of the offspring). Gene therapy in germline cells has the potential to affect not only the individual being treated, but also his or her children as well. Germline therapy would change the genetic pool of the entire human species, and future generations would have to live with that change.
Gene Therapy: requirements
The gene must be identified and cloned. This has been done for the ADA gene.It must be inserted in cells that can take up long-term residence in the patient. So far, this means removing the patient's own cells, treating them in tissue culture, and then returning them to the patient. It must be inserted in the DNA so that it will be expressed adequately; that is, transcribed and translated with sufficient efficiency that worthwhile amounts of the enzyme are produced. All these requirements seem to have been met for SCID therapy using a retrovirus as the gene vector. Retroviruses have several advantages for introducing genes into human cells. Their envelope protein enables the virus to infect human cells. RNA copies of the human ADA gene can be incorporated into the retroviral genome using a packaging cell.
is the insertion of genes into an individual's cells and tissues to treat a disease, and hereditary diseases in which a defective mutant allele is replaced with a functional one. Although the technology is still in its infancy, it has been used with some success. Antisense therapy is not strictly a form of gene therapy, but is a genetically-mediated therapy and is often considered together with other methods.
How does gene therapy work?
In most gene therapy studies, a "normal" gene is inserted into the genome to replace an "abnormal," disease-causing gene. A carrier molecule called a vector must be used to deliver the therapeutic gene to the patient's target cells. Currently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists have tried to take advantage of this capability and manipulate the virus genome to remove disease-causing genes and insert therapeutic genes.
Target cells such as the patient's liver or lung cells are infected with the viral vector. The vector then unloads its genetic material containing the therapeutic human gene into the target cell. The generation of a functional protein product from the therapeutic gene restores the target cell to a normal state.
How is gene therapy being studied in the treatment of cancer?
Researchers are studying several ways to treat cancer using gene therapy. Some approaches target healthy cells to enhance their ability to fight cancer. Other approaches target cancer cells, to destroy them or prevent their growth. Some gene therapy techniques under study are described below. In one approach, researchers replace missing or altered genes with healthy genes.
The types of gene therapy described thus far all have one factor in common: that is, that the tissues being treated are somatic (somatic cells include all the cells of the body, excluding sperm cells and egg cells). In contrast to this is the replacement of defective genes in the germline cells (which contribute to the genetic heritage of the offspring). Gene therapy in germline cells has the potential to affect not only the individual being treated, but also his or her children as well. Germline therapy would change the genetic pool of the entire human species, and future generations would have to live with that change.
Gene Therapy: requirements
The gene must be identified and cloned. This has been done for the ADA gene.It must be inserted in cells that can take up long-term residence in the patient. So far, this means removing the patient's own cells, treating them in tissue culture, and then returning them to the patient. It must be inserted in the DNA so that it will be expressed adequately; that is, transcribed and translated with sufficient efficiency that worthwhile amounts of the enzyme are produced. All these requirements seem to have been met for SCID therapy using a retrovirus as the gene vector. Retroviruses have several advantages for introducing genes into human cells. Their envelope protein enables the virus to infect human cells. RNA copies of the human ADA gene can be incorporated into the retroviral genome using a packaging cell.
DNA and RNA- The Strands of Life
Deoxyribonucleic Acid (DNA) is the component in a cell that is responsible for, perhaps, all functions within the cell and the organism. DNA stores and passes down information from one generation to the next. This is known as the genetic code.
DNA is a molecule, comprised of nucleotides, the monomers of DNA. Each nucleotide contains a phosphate group, a five-carbon sugar, and a nitrogen base. The five-carbon sugar in DNA is called deoxyribose. Each nucleotide will contain one of four n-bases: guanine, adenine, cytosine, and thymine. Guanine and Adenine are called purines, while cytosine and thymine are pyrimidines. In the structural formula for purines, there are two rings made up of nitrogen and in the pyrimidines, there is one ring made up of nitrogen.
The shape of DNA is a double helix, proposed by James Watson and Francis Crick. The name describes DNA's two strands that are twisted around one another. Base-pairing holds these two strands together. In base pairing, each nitrogen base of one of the strands bonds with a weak hydrogen bond to the n-base of another strand. guanine bonds with cytosine and adenine bonds with thymine. These n-bases form the "rungs" of the double helix or "twisted ladder." The sugar and phosphate groups form the outside of the ladder. The nitrogen bases are always bonded to the sugar. This base-sugar unit is referred to as a nucleoside. The phosphate groups link sugars together.
The process by which DNA copies itself is called replication. It is necessary for DNA to replicate to produce another generation. During replication, the DNA untwists itself. The weak hydrogen bonds between each of the n-bases break down the center. A new, complimentary nucleotide is placed with the orginal strand to form the new DNA. Finally the DNA coils again to its orginal shape.
Ribonucleic Acid (RNA) can be compared to an employer and an employee. DNA is the employer and RNA works for it. DNA does not leave the nucleus of a cell, so it must have a messanger to carry the genetic code to other places in the cell. RNA is much like DNA except the following things: RNA is a single strand and it contails uracil, rather than thymine. There are three types of RNA: messanger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Each has a specific purpose to carry out in the cell. The mRNA is made up of codons, a set of three n-bases. Each codon links to the original DNA strand and reads the genetic code by a process called transcription. The mRNA carries this message out of the nucleus and into the cytoplasm of the cell. tRNA bonds to mRNA with a peptide bond. tRNA is made up of anti-codons. These anti-codons bond to the codons, which tells them to pick up an amino acid, the monomer of proteins. After the amino acids are gathered, they build on the ribosomes, organelles that are made up of rRNA, of the cell. The ribosomes create proteins by a process known as protein synthesis. This process is probably the most important function of the DNA because proteins are the most important things in sustaining life.
DNA is not completely understood by scientists at this time. The more we can learn, the more genetic disorders we may prevent, and the more knowledge about life we will gain.
DNA is a molecule, comprised of nucleotides, the monomers of DNA. Each nucleotide contains a phosphate group, a five-carbon sugar, and a nitrogen base. The five-carbon sugar in DNA is called deoxyribose. Each nucleotide will contain one of four n-bases: guanine, adenine, cytosine, and thymine. Guanine and Adenine are called purines, while cytosine and thymine are pyrimidines. In the structural formula for purines, there are two rings made up of nitrogen and in the pyrimidines, there is one ring made up of nitrogen.
The shape of DNA is a double helix, proposed by James Watson and Francis Crick. The name describes DNA's two strands that are twisted around one another. Base-pairing holds these two strands together. In base pairing, each nitrogen base of one of the strands bonds with a weak hydrogen bond to the n-base of another strand. guanine bonds with cytosine and adenine bonds with thymine. These n-bases form the "rungs" of the double helix or "twisted ladder." The sugar and phosphate groups form the outside of the ladder. The nitrogen bases are always bonded to the sugar. This base-sugar unit is referred to as a nucleoside. The phosphate groups link sugars together.
The process by which DNA copies itself is called replication. It is necessary for DNA to replicate to produce another generation. During replication, the DNA untwists itself. The weak hydrogen bonds between each of the n-bases break down the center. A new, complimentary nucleotide is placed with the orginal strand to form the new DNA. Finally the DNA coils again to its orginal shape.
Ribonucleic Acid (RNA) can be compared to an employer and an employee. DNA is the employer and RNA works for it. DNA does not leave the nucleus of a cell, so it must have a messanger to carry the genetic code to other places in the cell. RNA is much like DNA except the following things: RNA is a single strand and it contails uracil, rather than thymine. There are three types of RNA: messanger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Each has a specific purpose to carry out in the cell. The mRNA is made up of codons, a set of three n-bases. Each codon links to the original DNA strand and reads the genetic code by a process called transcription. The mRNA carries this message out of the nucleus and into the cytoplasm of the cell. tRNA bonds to mRNA with a peptide bond. tRNA is made up of anti-codons. These anti-codons bond to the codons, which tells them to pick up an amino acid, the monomer of proteins. After the amino acids are gathered, they build on the ribosomes, organelles that are made up of rRNA, of the cell. The ribosomes create proteins by a process known as protein synthesis. This process is probably the most important function of the DNA because proteins are the most important things in sustaining life.
DNA is not completely understood by scientists at this time. The more we can learn, the more genetic disorders we may prevent, and the more knowledge about life we will gain.
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