BIO1140 Study Group #7 Answer Key

BIO1140 Study Group #7 Answer Key - BIO1140 Study Group#7...

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BIO1140 Study Group #7 Answer Key 1. i. The DNA structure is antiparallel. DNA strands go from 5 ʼ to 3 ʼ . ii. Synthesis follows the base-pairing rules, A-T, G-C. iii. One new DNA strand is synthesized continuously; the other, discontinuously iv. DNA polymerases are the primary enzymes of DNA replication. v. DNA replication begins at replication origins vi.RNA primers provide the starting point for DNA polymerase to begin synthesizing a new DNA chain 2. Helicase unwinds the DNA - Primase synthesizes RNA primer (starting point for nucleotide assembly by DNA polymerases) - DNA polymerases assemble nucleotides into a chain, remove primers, and fill resulting gaps - DNA ligase closes remaining single-chain nicks 3. Leading strand=continuous Lagging strand=discontinous -As DNA helix unwinds, one template strand runs in a direction allowing new DNA strand to be made continuously in the direction of unwinding - Other template strand is copied in short lengths that run in the direction opposite to unwinding - Discontinuous replication produces short lengths, then linked into a continuous strand 4. Q? Ends of eukaryotic chromosomes. What happens to them? - Short sequences repeated hundreds to thousands of times (Humans have ( TTAGGG )n ) - Repeats protect against chromosome shortening during replication - Chromosome shortening is prevented in some cell types which have a telomerase enzyme (adds telomere repeats to chromosome ends) 5. Mechanisms That Correct Errors - Errors inevitably occur, during replication or caused by DNA damage - Proofreading depends on the ability of DNA polymerases to reverse and remove mismatched bases - DNA repair corrects errors that escape proofreading or caused by DNA damaging agents
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Proofreading by DNA Polymerase: -If a replication error causes a base to be mispaired, DNA polymerase reverses and removes the most recently added bases.
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