22 Questions
What is the primary cause of spontaneous mutations in DNA?
Chemical instability of DNA components
What is the role of p50 protein in the DNA repair mechanism?
Ensuring damaged DNA and proteins are not replicated
What is the difference between apoptosis and necrosis?
Apoptosis is programmed cell death, while necrosis is caused by physical destruction
What is the ultimate consequence of DNA damage that is not repaired?
All of the above
What is the primary mechanism of DNA repair that corrects mismatches in DNA?
DNA mismatch repair
What is the result of unrepaired DNA damage?
Mutations in the DNA sequence
What is the role of DNA repair in maintaining genome integrity?
It repairs damaged DNA to maintain its integrity
What is the consequence of DNA replication errors?
Mutations in the DNA sequence
What is the primary function of DNA glycosylases in base excision repair?
To recognise and remove specific damaged or inappropriate bases
What is the result of non-homologous end joining repair?
Loss or occasional addition of a few nucleotides at the cut site
What is the purpose of DNA ligase in nucleotide excision repair?
To stick the 2 strands to form a double stranded nature
What is the role of DNA polymerases in nucleotide excision repair?
To synthesise a short complimentary sequence
What is the primary function of DNA mismatch repair?
To recognise and repair insertion, deletion and mis-incorporation of bases
What is the result of AP site formation in base excision repair?
Binding of polymerase for synthesis of nucleotides
What is the characteristic of non-homologous end joining repair?
It repairs DNA by directly re-joining the two broken ends of the chromosome
What is the consequence of non-homologous end joining repair?
Loss or occasional addition of a few nucleotides at the cut site
What type of DNA damage occurs when benzo[a]pyrene leads to insertion and covalent bond formation between the molecule and DNA?
Crosslink formation
Which type of DNA damage is characterized by defects in both DNA strands?
Double strand break
Which DNA repair pathway takes advantage of the double-stranded nature of the DNA molecule?
Excision repair
What is the primary function of photolyase enzyme in DNA repair?
Directly reversing pyrimidine dimer formation
Which type of DNA damage is not a direct result of ionizing radiation?
Crosslink formation
What is the general term for the repair of DNA backbone defects?
Strand break repair
Study Notes
Nucleotide Excision Repair
- Damage is detected by an enzyme, which leaves the undamaged DNA intact.
- DNA polymerases use the intact DNA as a template to synthesize a short complementary sequence.
- DNA ligase then joins the two strands to form a double-stranded nature.
Base Excision Repair
- Removes damaged bases that could cause mutations.
- Initiated by DNA glycosylases, which recognize and remove specific damaged or inappropriate bases.
- AP sites are formed, where polymerase binds to synthesize nucleotides.
DNA Mismatch Repair
- Recognizes and repairs insertion, deletion, and mis-incorporation of bases that occur during DNA replication.
- System for correcting errors that occur during DNA replication.
Non-Homologous End Joining Repair
- Repairs DNA by joining broken ends of the chromosome without a template.
- Enzymes bind and weld DNA pieces together, removing damaged or mismatched nucleotides with nucleases and resynthesizing with DNA polymerases.
- Can result in loss or addition of a few nucleotides at the cut site and often leads to mutations.
Mutations
- A randomly derived change to the nucleotide sequence of an organism's genetic material, causing a biological effect.
- 3 main causes: spontaneous, environmental, and genetic events.
Importance of DNA Repair
- DNA is the only biological macromolecule that is repaired, while others are replaced.
P50 Repair Mechanism
- Damage is detected, increasing p50 protein in the cell.
- Ensures damaged DNA and proteins are not replicated.
- p50 induces genes, leading to apoptosis and coordinating response between cell cycle and DNA repair.
Apoptosis vs Necrosis
- Apoptosis: programmed cell death, outer membrane remains intact and functional.
- Necrosis: caused by physical destruction to the cell membrane, leading to cell destruction.
Ionising Radiation Effects
- Causes single-strand breaks, double-strand breaks, base damage, and crosslinks.
DNA Repair Types
- 3 main types: direct reversal of damage, excision, and strand break repair.
- Examples: photoreactivation (direct reversal), nucleotide excision repair and base excision repair (excision), and non-homologous end joining repair (strand break repair).
This quiz covers the processes of Nucleotide Excision Repair and Base Excision Repair, which help maintain the integrity of DNA by correcting damages and mutations.
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