Chapter 25: Q20CP (page 909)
Must a carcinogen also be a mutagen?
Carcinogen causes significant mutation is the DNA and act as mutagen too.
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A high rate of base-substitution mutations can result from a polymerase’s tendency to incorporate a mispaired nucleotide or from its poor ability to incorporate the correct nucleotide. Use the following information about the catalytic efficiency (kcat/KM) of two error-prone polymerases to compare their ability substitution mutations.
| Polymerase | Template nucleotide | Incoming nucleotide | kcat/KM (µM . min-1 × 103 ) | |||
| Polymerase ƞ | T | T | A | G | 420 | 22 |
| HIV reverse transcriptase | T | T | A | G | 800 | 0.07 |
Ribonucleotides are erroneously incorporated into newly synthesized DNA as a result of incomplete primer removal or misincorporation by DNA polymerase. What types of enzymes would be required to remove and replace a single ribonucleotide in a DNA strand?
What fraction of the human genome consists of transposons and retrotransposons?
To put the replication system on a human scale, let us imagine that the-diameter B-DNA was expanded toin diameter. If everything were proportionally expanded, then each DNA polymerase holoenzyme would be about the size of a medium-sized truck. In such an expanded system: (a) How fast would each replisome be moving? (b) How far would each replisome travel during a complete replication cycle? (c) What would be the length of an Okazaki fragment? (d) What would be the average distance a replisome would travel between each error it made? Provide your answers in and .
Explain why interstrand DNA cross-links are much more mutagenic than intrastrand cross-links.
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