Lecture_15_-_DNA_Replication_Synthesis

Lecture_15_-_DNA_Replication_Synthesis - Lecture 15 Lecture...

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Lecture 15 Lecture 15 DNA DNA Replication Replication
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Accuracy of Replication Accuracy of Replication Replication is an essential function of genetic material and must be executed accurately if genetic continuity is maintained across generations The human genome has over 3 billion base pairs within its 23 haploid chromosomes An error rate of one in a million would produce a single replicated DNA strand with over 3,000 changes or ‘errors’ in its DNA sequence While a small number in terms of the total number of nucleotide bases, this could create extreme genotypic and phenotypic changes in the resulting offspring if gametes with this number of ‘errors’ combine during fertilization So, while not exact or error-free, DNA replication must be extremely accurate DNA replication is largely under genetic control and has evolved into a highly accurate system in most species
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Semiconservative Semiconservative Replication Replication There are three possible mechanisms for DNA replication and dispersion during cell division The first is called conservative replication . Conservative replication implies that two strands of DNA that make up a chromosome are copied or replicated in a cell. When cell division occurs the ‘new’ copies of the DNA form a new chromosome and this ‘new’ chromosome is transmitted to the ‘new’ daughter cell, while the original cell retains the original or ‘old’ DNA.
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Semiconservative Semiconservative Replication Replication The second possible type of replication is called dispersive replication . Dispersive replication implies that the two original DNA strands making up the ‘parental’ chromosome are completely separated during replication and each becomes a separate DNA strand. Each of the original strands are then copied and the original or ‘old’ strands and the ‘new’ strands randomly re-unite to form a new chromosome. Thus, the individual chromosomes of daughter cells may have two original strands of DNA, two replicated or ‘new’ strands or a combination of both. This is the most complicated of all possible types of replication and therefore the least likely to occur.
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Semiconservative Semiconservative Replication Replication The third possible type of DNA replication is called semiconservative replication . Semiconservative replication implies that the two DNA strands in each original parental chromosomes uncoil but do not separate. Each strand is replicated, then the ‘new’ replicated strand which is complementary to the ‘old’ strand from which it was copied, unites with the ‘old’ complementary strand to form a chromosome which has both ‘old’ and ‘new’ DNA strands This is in fact the most common form of DNA replication
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Basic Features of Replication Basic Features of Replication The synthesis of new DNA strands in humans occurs at a rate of about 3,000 nucleotides per minute; in bacteria about 30,000 nucleotides per
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Lecture_15_-_DNA_Replication_Synthesis - Lecture 15 Lecture...

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