Podcast
Questions and Answers
What distinguishes the parental strand from the new strand in DNA mismatch repair?
What distinguishes the parental strand from the new strand in DNA mismatch repair?
- The new strand contains a GATC sequence, while the parental strand does not.
- The parental strand is methylated, serving as a chemical marker. (correct)
- The parental strand lacks a sugar-phosphate backbone.
- The new strand is methylated, serving as a chemical marker.
In DNA mismatch repair, what is the role of GATC sites?
In DNA mismatch repair, what is the role of GATC sites?
- They serve as recognition sites for the repair system to locate and cut out the mismatched DNA segment. (correct)
- They are the locations where DNA ligase connects the 3' end of a chain to the 5' end.
- They serve as signals for glycosylase to cut out aberrant bases.
- They mark the A.P. sites on the DNA chain.
When does the DNA mismatch repair system primarily function during the cell cycle?
When does the DNA mismatch repair system primarily function during the cell cycle?
- G2 phase (correct)
- G1 phase
- S phase
- M phase
What is the consequence of damage in the MSH-2 gene?
What is the consequence of damage in the MSH-2 gene?
In base excision repair, what is the role of glycosylase?
In base excision repair, what is the role of glycosylase?
What is the initial step in base excision repair following the detection of an aberrant base?
What is the initial step in base excision repair following the detection of an aberrant base?
What type of sequence is methylated approximately every 1000 nucleotides in DNA?
What type of sequence is methylated approximately every 1000 nucleotides in DNA?
Which event leads to the formation of A.P. sites in DNA?
Which event leads to the formation of A.P. sites in DNA?
What type of strand is methylated when DNA replication is first completed?
What type of strand is methylated when DNA replication is first completed?
What is the function of DNA ligase in DNA repair?
What is the function of DNA ligase in DNA repair?
How does the mismatch repair system differentiate between the parental and newly synthesized DNA strands to correct errors?
How does the mismatch repair system differentiate between the parental and newly synthesized DNA strands to correct errors?
If a cell's DNA mismatch repair system is compromised, which of the following outcomes is most likely?
If a cell's DNA mismatch repair system is compromised, which of the following outcomes is most likely?
Besides the spontaneous loss of certain bases from DNA, what other process can cause A.P. sites?
Besides the spontaneous loss of certain bases from DNA, what other process can cause A.P. sites?
A researcher discovers a novel DNA polymerase with impaired proofreading ability. What is the anticipated consequence of using this polymerase in DNA replication?
A researcher discovers a novel DNA polymerase with impaired proofreading ability. What is the anticipated consequence of using this polymerase in DNA replication?
Considering the role of methylation in DNA repair, what would be the most likely effect of a drug that inhibits DNA methyltransferases on mismatch repair?
Considering the role of methylation in DNA repair, what would be the most likely effect of a drug that inhibits DNA methyltransferases on mismatch repair?
Base excision repair (BER) is initiated by DNA glycosylases that recognize and remove specific damaged bases, creating an apurinic/apyrimidinic (AP) site. After the creation of an AP site, what is the next step in the BER pathway?
Base excision repair (BER) is initiated by DNA glycosylases that recognize and remove specific damaged bases, creating an apurinic/apyrimidinic (AP) site. After the creation of an AP site, what is the next step in the BER pathway?
During mismatch repair in E. coli, the MutH protein nicks the unmethylated strand at a GATC site. What would be the most likely consequence if MutH nicks both strands at the GATC site?
During mismatch repair in E. coli, the MutH protein nicks the unmethylated strand at a GATC site. What would be the most likely consequence if MutH nicks both strands at the GATC site?
A researcher is studying the effects of various DNA repair mechanisms in a novel cell line. They observe that after inducing DNA damage via alkylation, the cells exhibit a significantly reduced survival rate. Which repair pathway is most likely deficient in this cell line?
A researcher is studying the effects of various DNA repair mechanisms in a novel cell line. They observe that after inducing DNA damage via alkylation, the cells exhibit a significantly reduced survival rate. Which repair pathway is most likely deficient in this cell line?
After exposure to UV radiation, a cell activates nucleotide excision repair (NER) to remove thymine dimers. What would be the most immediate and direct consequence if the TFIIH transcription factor were non-functional?
After exposure to UV radiation, a cell activates nucleotide excision repair (NER) to remove thymine dimers. What would be the most immediate and direct consequence if the TFIIH transcription factor were non-functional?
What would be the consequence of exposing cells to a chemical mutagen that specifically inhibits the activity of DNA ligase?
What would be the consequence of exposing cells to a chemical mutagen that specifically inhibits the activity of DNA ligase?
Flashcards
GATC Sequence
GATC Sequence
A specific nucleotide sequence (GATC) in DNA where adenine is methylated, occurring approximately every 1000 nucleotides.
DNA Semimethylation
DNA Semimethylation
The condition of a newly replicated DNA double helix where the parental strand is methylated, but the new strand is not.
DNA Mismatch Repair
DNA Mismatch Repair
A system that corrects nucleotide pair mismatches in new DNA, ensuring accuracy; methylation guides the correction.
DNA Polymerase
DNA Polymerase
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DNA Ligase
DNA Ligase
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MSH-2 Gene
MSH-2 Gene
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Base Excision Repair
Base Excision Repair
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AP Sites
AP Sites
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Glycosylase
Glycosylase
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Study Notes
- DNA repair occurs to fix errors and damage to DNA
DNA Repair Mechanisms
- Approximately every 1000 nucleotides, DNA possesses a GATC sequence where adenine is methylated
- After DNA replication, each new double helix is semimethylated
- The parental strand is methylated, but the new strand is not yet methylated
Mismatch Repair System
- Consists of several proteins active during the G2 phase of the cell cycle
- This protein complex scans new DNA double helices for nucleotide pair mismatches
- If a mismatch is found, the repair system identifies the parental strand and the new strand to correct errors in the new strand
- Parental strand methylation serves as a chemical marker
- After identifying the mismatch and the new strand, the mismatch repair system locates the nearest GATC sites both proximal and distal to the mismatch point
- The system then excises the section of new DNA between these two GATC areas
- DNA polymerase then elongates DNA from the 5' to 3' direction
- DNA ligase then connects the 3' end of the chain to the 5' end of the rest of the chain
MSH-2 Gene
- The primary gene involved in mismatch repair
- Damage to this gene often leads to Hereditary Non-Polyposis Colon Cancer
Base Excision Repair
- Another type of DNA repair system, occurring at AP sites
- AP sites are apurinic sites that typically form in two ways
- Purines (adenine and guanine) spontaneously fall out, leaving the sugar-phosphate backbone intact
- Nitrates and nitrites can cause deamination of cytosine, turning it into uracil
- When an aberrant base is detected, glycosylase cuts it out, leaving an AP site
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