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Dr. Howe Study Guid # 3


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- Mechanism that helps keep the frequency of DNA replication errors low
DNA polymerase
3' to 5' exonuclease activity. Both polymerase I and III (proofreading).
-base pair are not complementary.
-DNA polymerase makes a mistake
Mismatch repair
identify mismatch and excise miss paired nucleotide and replace it with correct nucleotide.
DNA polymerase I- 5' to 3' activeity can remove neleotide from the 5' end of the DNA or from the RNA primer strand.
DNA polymerase III and I has 5'to 3' exonuclease proofreading activity.
Any detectable and heritable change in the genetic material not caused by genetic recombination.
-change in DNA nucleotide
When can mutations occur?
when DNA pol makes a mistake
What is the error rate of DNA polymerase before and after proofreading by DNA polymerase?
1/10^5 nucleotides
In relation to the process of replication, when do proofreading and mismatch repair occur?
The 3' to 5' exonulease activity excises the wrong nucleotide on the new strand. Then the 5' to 3' DNA polymerase activity the resumes forward direction and inserts the correct nucleotide
In mismatch repair, how is the newly synthesized strand distinguished from the original parent strand?
The polymerase proofreads each neucleotide against its template as soon as it is added to the strand
What is the DNA relication error rate after mismatch repair?
1/10^7 nucleotide
Methylation in Prokaryotes
Newly made DNA gets methylated (after replication).
- The unmethylated gets identifed and the nucleotides are removed
Methylation in Eukaryotes
After replication the new DNA is nicked at the phosphodiester bonds.
They are identified by mismatch repair.

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