Podcast
Questions and Answers
What is the primary function of DNA photolyase in direct reversal repair?
What is the primary function of DNA photolyase in direct reversal repair?
- It removes methyl groups from guanine residues.
- It breaks covalent bonds using energy from light. (correct)
- It detects uracil bases within DNA.
- It cleaves DNA backbone at abasic sites.
Which enzyme is responsible for detecting the presence of uracil bases in DNA during base excision repair?
Which enzyme is responsible for detecting the presence of uracil bases in DNA during base excision repair?
- Uracil glycosylase (correct)
- DNA ligase
- DNA polymerase
- AP endonuclease
What happens after the methyl group is transferred from guanine by methyltransferase?
What happens after the methyl group is transferred from guanine by methyltransferase?
- It becomes inactive and can no longer function. (correct)
- It forms a permanent bond with DNA.
- It activates another DNA repair mechanism.
- It directly repairs the DNA structure.
In base excision repair, what role does DNA polymerase play?
In base excision repair, what role does DNA polymerase play?
What type of damage does base excision repair address?
What type of damage does base excision repair address?
Flashcards
Photoreactivation
Photoreactivation
A DNA repair mechanism that directly reverses the formation of pyrimidine dimers, often caused by UV radiation. This process uses energy from light to break the covalent bonds within the dimer.
Base excision repair
Base excision repair
This repair method removes damaged or incorrect bases from DNA through a series of enzymatic steps. It involves specific enzymes called DNA glycosylases that recognize and remove the damaged base, leaving an abasic site. This site is then further processed by other enzymes, including AP endonuclease and AP lyase, to create a gap in the DNA backbone. Finally, DNA polymerase and ligase fill in the gap and seal the break, restoring the DNA to its original sequence.
Uracil glycosylase
Uracil glycosylase
A key enzyme in base excision repair that specifically recognizes and removes uracil bases from DNA. Uracil is not a normal component of DNA and can arise from the deamination of cytosine.
Demethylation
Demethylation
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T-G mismatch repair
T-G mismatch repair
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Study Notes
DNA Repair Mechanisms
- Direct Reversal Repair: Directly reverses pyrimidine dimer formation.
- Also known as "light repair."
- DNA photolyase uses light energy to break covalent bonds.
- Demethylation: Methyltransferases remove methyl groups from guanine.
- The methyl group is transferred to a cysteine residue in the protein.
- This inactivates the methyltransferase (one-time use).
- However, the protein can activate the gene encoding the methyltransferase (self-regulation).
- Photoreactivation: A specific type of direct reversal repair.
Base Excision Repair
- Repairs single-base mismatches and damaged bases (e.g., deamination, alkylation, oxidation).
- Involves specific DNA glycosylases (e.g., uracil glycosylase).
- These enzymes detect abnormal bases (e.g., uracil).
- They remove the incorrect base by flipping it out of the DNA backbone and cleaving its bond to the sugar-phosphate backbone (creating an abasic site).
- Abasic sites are further processed.
- AP endonuclease cleaves the DNA backbone 5' to the damage.
- AP lyase cleaves the backbone 3' to the damage.
- The gap is filled by DNA polymerase and DNA ligase.
- DNA glycosylases can recognize T-G mismatches.
- Often caused by deamination of methylated cytosine.
- The resulting thymine is mismatched with guanine.
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Description
Test your knowledge on the various DNA repair mechanisms, including direct reversal repair, base excision repair, and their specific processes. This quiz covers key concepts such as photoreactivation, demethylation, and the roles of DNA glycosylases. Perfect for students studying molecular biology or genetics!
