BIO130 Section One Guide (5)

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Kenneth Yip

Chapter 5 DNA Replication, Repair, and Recombination (pg. 263-288, 292-304) The Maintenance of DNA Sequences Mutation Rates are Extremely Low - Mutation rate rate at which observable changes occur in DNA sequences 3 o A single genes that encodes an average-sized protein ( 10 nucleotide pairs) accumulates a mutation about once in about 10 bacterial cell generations - Comparing amino acid sequences of the same protein in several species can provide an estimate of mutation rates in mammals; because natural selection causes mutations to vanish from the population, these tend to be underestimates - Luckily, the sequence of one family of protein fragments (fibrinopeptides) does not seem to matter, allowing the encoding genes to accumulate mutations without being selected against - Fibrinopeptides fragments 20 AA long that are discarded when the protein fibrinogen is activated to form fibrin during blood clotting o Because the function of fibrinopeptides doesnt depend on its AA sequence, it can tolerate almost any mutation - Another way to estimate mutation rates is to compare DNA sequences between related species Low Mutation Rates are Necessary for Life as We Know It - Deleterious mutations limit the number to essential proteins an organism can encode (50,000) o A mutation rate 10X high would limit an organism to about 5000 essential genes - Germ cells transmit genetic information from parent to offspring - Somatic cells form the body of the organism - Uncontrolled cell proliferation of somatic cells causes cancer, causing more than 20% of deaths each year in Europe and North America - Multicellular organisms depend on the high fidelity their DNA sequences are replicated and maintained for both the survival of their large number of genes (germ cell stability) and the prevention of cancer caused by mutations in somatic cells (somatic cell stability) DNA Replication Mechanisms - DNA is replicated at up to 1000 nucleotidessecond Base-Pairing Underlies DNA Replication and DNA Repair
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