Mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or viruses, or can occur deliberately under cellular control during processes such as hypermutation. In multicellular organisms, mutations can be subdivided into germ line mutations, which can be passed on to descendants, and somatic mutations, which are not transmitted to descendants in animals. Plants sometimes can transmit somatic mutations to their descendants asexually or sexually (in case when flower buds develop in somatically mutated part of plant). A new mutation that was not inherited from either parent is called a de novo mutation.
Mutations create variations in the gene pool. Less favorable (or deleterious) mutations can be reduced in frequency in the gene pool by natural selection, while more favorable (beneficial or advantageous) mutations may accumulate and result in adaptive evolutionary changes. For example, a butterfly may produce offspring with new mutations. Many times those are have no effect; but one might change the color of one of the butterfly's offspring, making it harder (or easier) for predators to see. If this color change is advantageous, the chance of this butterfly surviving and producing its own offspring are a little better, and over time the number of butterflies with this mutation may form a larger percentage of the population.
Neutral mutations are defined as mutations whose effects do not influence the fitness of an individual. These can accumulate over time due to genetic drift. It is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness. Also, DNA repair mechanisms are able to mend most changes before they become permanent mutations, and many organisms have mechanisms for eliminating otherwise permanently mutated somatic cells.
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Showing posts with label DNA MUTATION. Show all posts
Showing posts with label DNA MUTATION. Show all posts
Wednesday, December 17, 2008
Mismatch Repair
Dna polymerase copies both strand of DNA the top strand and bottom strand, sometimes these stands are called Watson and crick strand. But these strands are not perfect, Normally A opposite tot and G opposite to C.Sometimes these make mistakes in copies wrong nucleotide for example T is copied For G where C should be copied potential mutation fortunately cells have repair system that can erase the mutations and those repair protein are called PMS2, MLH1, MSH2, MSH6, these enzyme recruit another enzyme called EX01 (exonulcease), which choppes off the mutant strand and allows dna polymerase to synthesis the correct strand and there by fixing out DNA
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Email me : help.me.ishan@gmail.com
DNA
Deoxyribonucleic acid (DNA) is a nucleic acid molecule consisting of long chains of polymerized (deoxyribo) nucleotides. In double-stranded DNA the two strands are held together by hydrogen bonds between complementary nucleotide base pairs.
DNA was discovered in 1869 by Johann Friedrich Miescher, a Swiss biochemist working in Tubigen, Germany, The first extracts that Miescher made from human white blood cells were crude mixtures of DNA and chromosomal proteins. Next year he prepared a pure sample of nucleic acid from Salomon sperm, The chemical test showed that DNA is acidic and rich in phosphorus, and also suggested that the individual molecules are very large, although it was not until the 1930s when biophysical techniques are applied to DNA that huge lengths of polymeric chains were fully appreciated.
The basic building block of nucleic acids is the nucleotide. This has three components:
* a nitrogenous base;
* a sugar;
* and a phosphate.
The nitrogenous base is a purine or pyrimidine ring. The base is linked to position 1 on a pentose sugar by a glycosidic bond from N1 of pyrimidines or N9 of purines. To avoid ambiguity between the numbering systems of the heterocyclic rings and the sugar, positions on the pentose are given a prime ().
Nucleic acids are named for the type of sugar; DNA has 2–deoxyribose, whereas RNA has ribose. The difference is that the sugar in RNA has an OH group at the 2 position of the pentose ring. The sugar can be linked by its 5 or 3 position to a phosphate group.
A nucleic acid consists of a long chain of nucleotides. the backbone of the polynucleotide chain consists of an alternating series of pentose (sugar) and phosphate residues. This is constructed by linking the 5 position of one pentose ring to the 3 position of the next pentose ring via a phosphate group. So the sugar-phosphate backbone is said to consist of 5–3 phosphodiester linkages. The nitrogenous bases "stick out" from the backbone.
Each nucleic acid contains 4 types of base. The same two purines, adenine and guanine, are present in both DNA and RNA. The two pyrimidines in DNA are cytosine and thymine; in RNA uracil is found instead of thymine. The only difference between uracil and thymine is the presence of a methyl substituent at position C5. The bases are usually referred to by their initial letters. DNA contains A, G, C, T, while RNA contains A, G, C, U.
The terminal nucleotide at one end of the chain has a free 5 group; the terminal nucleotide at the other end has a free 3 group. It is conventional to write nucleic acid sequences in the 5→3 direction—that is, from the 5 terminus at the left to the 3 terminus at the right.
The replication process is initiated at particular points within the DNA, known as "origins", which are targeted by proteins that separate the two strands and initiate DNA synthesis.Origins contain DNA sequences recognized by replication initiator proteins (eg. dnaA in E coli' and the Origin Recognition Complex in yeast). These initiator proteins recruit other proteins to separate the two strands and initiate replication forks.
Initiator proteins recruit other proteins to separate the DNA strands at the origin, forming a bubble. Origins tend to be "AT-rich" (rich in adenine and thymine bases) to assist this process because A-T base pairs have two hydrogen bonds (rather than the three formed in a C-G pair)—strands rich in these nucleotides are generally easier to separate. Once strands are separated, RNA primers are created on the template strands and DNA polymerase extends these to create newly synthesized DNA.
As DNA synthesis continues, the original DNA strands continue to unwind on each side of the bubble, forming replication forks. In bacteria, which have a single origin of replication on their circular chromosome, this process eventually creates a "theta structure" (resembling the Greek letter theta: θ). In contrast, eukaryotes have longer linear chromosomes and initiate replication at multiple origins within these.
The replication fork
The replication fork is a structure which forms when DNA is being replicated. It is created through the action of helicase, which breaks the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA.
Leading strand synthesis
In DNA replication, the leading strand is defined as the new DNA strand at the replication fork that is synthesized in the 5'→3' direction in a continuous manner. When the enzyme helicase unwinds DNA, two single stranded regions of DNA (the "replication fork") form. On the leading strand DNA polymerase III is able to synthesize DNA using the free 3' OH group donated by a single RNA primer and continuous synthesis occurs in the direction in which the replication fork is moving.
Lagging strand synthesis
The lagging strand is the DNA strand at the opposite side of the replication fork from the leading strand, running in the 3' to 5' direction. Because DNA polymerase cannot synthesize in the 3'→5' direction, the lagging strand is synthesized in short segments known as Okazaki fragments. Along the lagging strand's template, primase builds RNA primers in short bursts. DNA polymerases are then able to use the free 3' OH groups on the RNA primers to synthesize DNA in the 5'→3' direction. The RNA fragments are then removed (different mechanisms are used in eukaryotes and prokaryotes) and new deoxyribonucleotides are added to fill the gaps where the RNA was present. DNA ligase then joins the deoxyribonucleotides together, completing the synthesis of the lagging strand.
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DNA was discovered in 1869 by Johann Friedrich Miescher, a Swiss biochemist working in Tubigen, Germany, The first extracts that Miescher made from human white blood cells were crude mixtures of DNA and chromosomal proteins. Next year he prepared a pure sample of nucleic acid from Salomon sperm, The chemical test showed that DNA is acidic and rich in phosphorus, and also suggested that the individual molecules are very large, although it was not until the 1930s when biophysical techniques are applied to DNA that huge lengths of polymeric chains were fully appreciated.
The basic building block of nucleic acids is the nucleotide. This has three components:
* a nitrogenous base;
* a sugar;
* and a phosphate.
The nitrogenous base is a purine or pyrimidine ring. The base is linked to position 1 on a pentose sugar by a glycosidic bond from N1 of pyrimidines or N9 of purines. To avoid ambiguity between the numbering systems of the heterocyclic rings and the sugar, positions on the pentose are given a prime ().
Nucleic acids are named for the type of sugar; DNA has 2–deoxyribose, whereas RNA has ribose. The difference is that the sugar in RNA has an OH group at the 2 position of the pentose ring. The sugar can be linked by its 5 or 3 position to a phosphate group.
A nucleic acid consists of a long chain of nucleotides. the backbone of the polynucleotide chain consists of an alternating series of pentose (sugar) and phosphate residues. This is constructed by linking the 5 position of one pentose ring to the 3 position of the next pentose ring via a phosphate group. So the sugar-phosphate backbone is said to consist of 5–3 phosphodiester linkages. The nitrogenous bases "stick out" from the backbone.
Each nucleic acid contains 4 types of base. The same two purines, adenine and guanine, are present in both DNA and RNA. The two pyrimidines in DNA are cytosine and thymine; in RNA uracil is found instead of thymine. The only difference between uracil and thymine is the presence of a methyl substituent at position C5. The bases are usually referred to by their initial letters. DNA contains A, G, C, T, while RNA contains A, G, C, U.
The terminal nucleotide at one end of the chain has a free 5 group; the terminal nucleotide at the other end has a free 3 group. It is conventional to write nucleic acid sequences in the 5→3 direction—that is, from the 5 terminus at the left to the 3 terminus at the right.
The replication process is initiated at particular points within the DNA, known as "origins", which are targeted by proteins that separate the two strands and initiate DNA synthesis.Origins contain DNA sequences recognized by replication initiator proteins (eg. dnaA in E coli' and the Origin Recognition Complex in yeast). These initiator proteins recruit other proteins to separate the two strands and initiate replication forks.
Initiator proteins recruit other proteins to separate the DNA strands at the origin, forming a bubble. Origins tend to be "AT-rich" (rich in adenine and thymine bases) to assist this process because A-T base pairs have two hydrogen bonds (rather than the three formed in a C-G pair)—strands rich in these nucleotides are generally easier to separate. Once strands are separated, RNA primers are created on the template strands and DNA polymerase extends these to create newly synthesized DNA.
As DNA synthesis continues, the original DNA strands continue to unwind on each side of the bubble, forming replication forks. In bacteria, which have a single origin of replication on their circular chromosome, this process eventually creates a "theta structure" (resembling the Greek letter theta: θ). In contrast, eukaryotes have longer linear chromosomes and initiate replication at multiple origins within these.
The replication fork
The replication fork is a structure which forms when DNA is being replicated. It is created through the action of helicase, which breaks the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA.
Leading strand synthesis
In DNA replication, the leading strand is defined as the new DNA strand at the replication fork that is synthesized in the 5'→3' direction in a continuous manner. When the enzyme helicase unwinds DNA, two single stranded regions of DNA (the "replication fork") form. On the leading strand DNA polymerase III is able to synthesize DNA using the free 3' OH group donated by a single RNA primer and continuous synthesis occurs in the direction in which the replication fork is moving.
Lagging strand synthesis
The lagging strand is the DNA strand at the opposite side of the replication fork from the leading strand, running in the 3' to 5' direction. Because DNA polymerase cannot synthesize in the 3'→5' direction, the lagging strand is synthesized in short segments known as Okazaki fragments. Along the lagging strand's template, primase builds RNA primers in short bursts. DNA polymerases are then able to use the free 3' OH groups on the RNA primers to synthesize DNA in the 5'→3' direction. The RNA fragments are then removed (different mechanisms are used in eukaryotes and prokaryotes) and new deoxyribonucleotides are added to fill the gaps where the RNA was present. DNA ligase then joins the deoxyribonucleotides together, completing the synthesis of the lagging strand.
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Saturday, December 13, 2008
DNA
Deoxyribonucleic acid (DNA) is a nucleic acid molecule consisting of long chains of polymerized (deoxyribo) nucleotides. In double-stranded DNA the two strands are held together by hydrogen bonds between complementary nucleotide base pairs.
DNA was discovered in 1869 by Johann Friedrich Miescher, a Swiss biochemist working in Tubigen, Germany, The first extracts that Miescher made from human white blood cells were crude mixtures of DNA and chromosomal proteins. Next year he prepared a pure sample of nucleic acid from Salomon sperm, The chemical test showed that DNA is acidic and rich in phosphorus, and also suggested that the individual molecules are very large, although it was not until the 1930s when biophysical techniques are applied to DNA that huge lengths of polymeric chains were fully appreciated.
The basic building block of nucleic acids is the nucleotide. This has three components:
a nitrogenous base;
a sugar;
and a phosphate.
The nitrogenous base is a purine or pyrimidine ring. The base is linked to position 1 on a pentose sugar by a glycosidic bond from N1 of pyrimidines or N9 of purines. To avoid ambiguity between the numbering systems of the heterocyclic rings and the sugar, positions on the pentose are given a prime ().
Nucleic acids are named for the type of sugar; DNA has 2–deoxyribose, whereas RNA has ribose. The difference is that the sugar in RNA has an OH group at the 2 position of the pentose ring. The sugar can be linked by its 5 or 3 position to a phosphate group.
A nucleic acid consists of a long chain of nucleotides. the backbone of the polynucleotide chain consists of an alternating series of pentose (sugar) and phosphate residues. This is constructed by linking the 5 position of one pentose ring to the 3 position of the next pentose ring via a phosphate group. So the sugar-phosphate backbone is said to consist of 5–3 phosphodiester linkages. The nitrogenous bases "stick out" from the backbone.
Each nucleic acid contains 4 types of base. The same two purines, adenine and guanine, are present in both DNA and RNA. The two pyrimidines in DNA are cytosine and thymine; in RNA uracil is found instead of thymine. The only difference between uracil and thymine is the presence of a methyl substituent at position C5. The bases are usually referred to by their initial letters. DNA contains A, G, C, T, while RNA contains A, G, C, U.
The terminal nucleotide at one end of the chain has a free 5 group; the terminal nucleotide at the other end has a free 3 group. It is conventional to write nucleic acid sequences in the 5→3 direction—that is, from the 5 terminus at the left to the 3 terminus at the right.
The replication process is initiated at particular points within the DNA, known as "origins", which are targeted by proteins that separate the two strands and initiate DNA synthesis.Origins contain DNA sequences recognized by replication initiator proteins (eg. dnaA in E coli' and the Origin Recognition Complex in yeast). These initiator proteins recruit other proteins to separate the two strands and initiate replication forks.
Initiator proteins recruit other proteins to separate the DNA strands at the origin, forming a bubble. Origins tend to be "AT-rich" (rich in adenine and thymine bases) to assist this process because A-T base pairs have two hydrogen bonds (rather than the three formed in a C-G pair)—strands rich in these nucleotides are generally easier to separate. Once strands are separated, RNA primers are created on the template strands and DNA polymerase extends these to create newly synthesized DNA.
As DNA synthesis continues, the original DNA strands continue to unwind on each side of the bubble, forming replication forks. In bacteria, which have a single origin of replication on their circular chromosome, this process eventually creates a "theta structure" (resembling the Greek letter theta: θ). In contrast, eukaryotes have longer linear chromosomes and initiate replication at multiple origins within these.
The replication fork
The replication fork is a structure which forms when DNA is being replicated. It is created through the action of helicase, which breaks the hydrogen bonds holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA.
Leading strand synthesis
In DNA replication, the leading strand is defined as the new DNA strand at the replication fork that is synthesized in the 5'→3' direction in a continuous manner. When the enzyme helicase unwinds DNA, two single stranded regions of DNA (the "replication fork") form. On the leading strand DNA polymerase III is able to synthesize DNA using the free 3' OH group donated by a single RNA primer and continuous synthesis occurs in the direction in which the replication fork is moving.
Lagging strand synthesis
The lagging strand is the DNA strand at the opposite side of the replication fork from the leading strand, running in the 3' to 5' direction. Because DNA polymerase cannot synthesize in the 3'→5' direction, the lagging strand is synthesized in short segments known as Okazaki fragments. Along the lagging strand's template, primase builds RNA primers in short bursts. DNA polymerases are then able to use the free 3' OH groups on the RNA primers to synthesize DNA in the 5'→3' direction. The RNA fragments are then removed (different mechanisms are used in eukaryotes and prokaryotes) and new deoxyribonucleotides are added to fill the gaps where the RNA was present. DNA ligase then joins the deoxyribonucleotides together, completing the synthesis of the lagging strand.
How Sex Leads To Variation Lecture
Scope this lecture continues their discretion of mentors contribution to genetics turned and the subsequent experiments in which Mendel looked at the transmission of more than one trait, leading to an of independent assortment. The lecture summarizes in the wind us up and, linkage, and crossover, all of which result from the way chromosome and the gene located on them move during gamete formation and sexual reproduction. The lecture concludes by recapping the sources that contribute to genetic variation that is essential for evolution to occur.
Part 1
Part 2
Part 3
Outline
I. Mendel continued his space experiment by crossing pea plants that are too phenotypic differences instead of one. From these dihybrid crosses, Mendel inferred additional properties of three transmission from the parents to offspring, properties consistent with knowledge gained later the moment of genes on chromosomes.
A. as wit flower color, seed color in pea plants depend on the single gene with two alleles: the Dominant yellow allele(Y) in the recessive gene allele(y).
B. space for example, when crossing the female pea plant with purple flowers and yellow seeds with the male pea plant with white flowers and green seats, we know that females genotype is PPYY in the male genotype is ppyy.
C.F1 individuals will have purple flower and a yellow seeds, because they are all heterozygous for both traits. As in monohybrid cross, the recessive traits disappeared in F1.
D. when F1 individuals makes gametes, do the allels from the original parents stay together or are they separated next?
If parent alleles are linked, an F1 space individual could produce only PY and py gametes;F2 would then contain only two parental phenotypes. Furthermore, these people takes would have the same 3:1 ratio as in monohybrid cross. This would mean that sets of parent alleles acted as a single alleles.
If parental alleles are not linked,F1 individuals would produce for better gamete in equal proportions:PY,py,Py,pY. A punnet Square using these gametes asserting 16 possible combinations and 9 distinctive F2 genotypes. These nine genotypes would produce 4 possible phenotypes, which would occur in 9: 3:3:1 ratio. Two of these phenotypes would not have existed in parent the generation; these so-called recombinant phenotypes.
Mendel observed 4 phenotypes in a 9:3:3:1 ratio in his F2 generation, which he correctly concluded to mean that alleles of inherited independently of each other.
E. from this conclusion, mendel formatted what is known as law of independent assortment, which simply says that Alleles off different genes segregating independently of each other during gamete formation.
II. Integral assortment of genes during meiosis is an important source of genetic variation.
During first meiotic division, homologues chromosomes line up in the cell and separated into two daughter cells. The assortment of Maternal and parent homology’s for1 chromosome has more effect on the assortment of any other chromosome.
In the genes of two different traits are on different chromosomes, they will assort independently of each other, as Mendel saw, and independent assortment produce recombinant phenotypes.
The number of unique combination of alleles on different chromosome can be very. Humans have 23 pairs of chromosomes; the possible number of assortment is 2(23) or about 8.4 million.
Independent assortment is different from mutation as a source of variation.
Mutation essentially generates new alleles-usually dysfunctional but not always.
Independent assortment does not create new alleles but, rather, new assortment of alleles.
However, both mutation and Independent assortment can change their phenotypes of successive generations.
III. if two genes occur on the same chromosome, an obvious conclusion is that they will be transmitted together as a unit during meiosis. Such genes are called linked genes.
During meiosis, however, homologue pairs of chromosomes associated so closely that they can exchange genetic material, which called crossing over. If linked gene crossover to other chromosome, they can assort independently.
Geneticists expanding on Mendel's work found that in the Everett tosses, F2 generation with linked genes would occasionally produce recombinant phenotypes, though a far fewer number than if the genes unlinked. Link genes, however, should not produce any recombinant phenotypes.
The further apart to genes on the chromosome, the more likely crossing over and recombinant phenotypes with be.
IV. Space though essentially established the sciences of genetics, Mendel’s work was ignored for about 40 years, because nothing was then known of the physical basis of mentors heritable factors and because he used advanced probability mathematics to calculate is ratio. Only when biologists began to see the pattern Mendel described did anyone realize that this work might be significant.
Part 1
Part 2
Part 3
Outline
I. Mendel continued his space experiment by crossing pea plants that are too phenotypic differences instead of one. From these dihybrid crosses, Mendel inferred additional properties of three transmission from the parents to offspring, properties consistent with knowledge gained later the moment of genes on chromosomes.
A. as wit flower color, seed color in pea plants depend on the single gene with two alleles: the Dominant yellow allele(Y) in the recessive gene allele(y).
B. space for example, when crossing the female pea plant with purple flowers and yellow seeds with the male pea plant with white flowers and green seats, we know that females genotype is PPYY in the male genotype is ppyy.
C.F1 individuals will have purple flower and a yellow seeds, because they are all heterozygous for both traits. As in monohybrid cross, the recessive traits disappeared in F1.
D. when F1 individuals makes gametes, do the allels from the original parents stay together or are they separated next?
If parent alleles are linked, an F1 space individual could produce only PY and py gametes;F2 would then contain only two parental phenotypes. Furthermore, these people takes would have the same 3:1 ratio as in monohybrid cross. This would mean that sets of parent alleles acted as a single alleles.
If parental alleles are not linked,F1 individuals would produce for better gamete in equal proportions:PY,py,Py,pY. A punnet Square using these gametes asserting 16 possible combinations and 9 distinctive F2 genotypes. These nine genotypes would produce 4 possible phenotypes, which would occur in 9: 3:3:1 ratio. Two of these phenotypes would not have existed in parent the generation; these so-called recombinant phenotypes.
Mendel observed 4 phenotypes in a 9:3:3:1 ratio in his F2 generation, which he correctly concluded to mean that alleles of inherited independently of each other.
E. from this conclusion, mendel formatted what is known as law of independent assortment, which simply says that Alleles off different genes segregating independently of each other during gamete formation.
II. Integral assortment of genes during meiosis is an important source of genetic variation.
During first meiotic division, homologues chromosomes line up in the cell and separated into two daughter cells. The assortment of Maternal and parent homology’s for1 chromosome has more effect on the assortment of any other chromosome.
In the genes of two different traits are on different chromosomes, they will assort independently of each other, as Mendel saw, and independent assortment produce recombinant phenotypes.
The number of unique combination of alleles on different chromosome can be very. Humans have 23 pairs of chromosomes; the possible number of assortment is 2(23) or about 8.4 million.
Independent assortment is different from mutation as a source of variation.
Mutation essentially generates new alleles-usually dysfunctional but not always.
Independent assortment does not create new alleles but, rather, new assortment of alleles.
However, both mutation and Independent assortment can change their phenotypes of successive generations.
III. if two genes occur on the same chromosome, an obvious conclusion is that they will be transmitted together as a unit during meiosis. Such genes are called linked genes.
During meiosis, however, homologue pairs of chromosomes associated so closely that they can exchange genetic material, which called crossing over. If linked gene crossover to other chromosome, they can assort independently.
Geneticists expanding on Mendel's work found that in the Everett tosses, F2 generation with linked genes would occasionally produce recombinant phenotypes, though a far fewer number than if the genes unlinked. Link genes, however, should not produce any recombinant phenotypes.
The further apart to genes on the chromosome, the more likely crossing over and recombinant phenotypes with be.
IV. Space though essentially established the sciences of genetics, Mendel’s work was ignored for about 40 years, because nothing was then known of the physical basis of mentors heritable factors and because he used advanced probability mathematics to calculate is ratio. Only when biologists began to see the pattern Mendel described did anyone realize that this work might be significant.
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