DNA Replication And Repair Flashcards
What is the difference between exonuclease and endonuclease?
- Exonuclease: remove nucleotides
- Endonuclease: release nucleic acid fragments
(Both hydrolyze PDE bonds)
Mention 3 differences between replication and synthesis of RNA
- “Proofreading” - DNA pol does (exonuclease 3’➡️5’), RNA pol doesn’t
- Primer - DNA pol need it, RNA pol doesn’t
- Substrates - dMNP for DNA pol, MNP for RNA pol
Facts in common between replication and RNA synthesis
- New strand synthesized 5’➡️3’
- Template strand scanned 3’➡️5’
- New strand complementary and antiparallel to the template
What do the quinolones, acid nalidixic (in bacterias) and etoposide, teniposide (in eukaryotic) share based on their mechanism of action?
- Block and inhibit the prokaryotic topoisomerase II (DNA gyrase) - bacteria
- Inhibit eukaryotic topoisomerase II - anticancer drugs
Why are the cancer cells immortals based on their chromosomes and replication?
They have high levels of Telomerase - avoid shortened of the telomeres
How does the AZT prevent further replication causing chain termination?
Replacement of azide instead normal OH group at 3’ of the deoxyribose. (Reverse transcriptase not proofreading)
*other drugs inhibiting DNA synthesis by reverse transcriptase in HIV - ddC, ddI
In what cases does the eukaryotic cells have reverse transcriptase activity?
- Telomerase (hTRT)
* Encoded by retrotransposons - amplify certain repetitive sequences in DNA
What is the cause of Xeroderma Pigmentosum? Symptoms.
- Deficiency of Excision Endonnuclease
- symptoms:
- excessive freckling
- extreme UV sensitivity
- multiple skin cancer
- corneal ulcerations
What type of damage is not corrected in Hereditary nonpolyposis colorectal cancer (HNPCC)? Why?
Mismatch base - because inherited and somatic mutation of hMLH1 or hMSH2 (make DNA mismatch repair - detect and remove errors during replication)
Ultimately what type of error of the replication we can see in HNPCC?
Microsatellite instability
