Chapter 4: 4.6 Repair of DNA Mutations Flashcards
True or False:
DNA Polymerase III can proofread the newly synthesized strand and correct mistakes
True
How does DNA polymerase III proofread?
Exonuclease activity
DNA Polymerase III proofreading prevents…
Mutations from staying in the DNA and being passed on to daughter cells
What can exonuclease activity do?
Break phosphodiester bonds to correct mistakes
What direction does DNA polymerase III synthesize and correct?
- Synthesizes 5’ to 3’
- Corrects 3’ to 5’
How does DNA polymerase III recognize improper placements of bases?
Detecting changes in geometry of improper base pairing as it polymerizes the complementary strand
If DNA Polymerase does not correct mismatched bases during DNA polymerization, what happens?
DNA Mismatch Repair
Describe:
DNA Mismatch Repair
- Specific DNA repair enzymes (endonucleases) recognize the incorrect geometry and repair the DNA by excising the incorrect nucleotide
- The gap is filled in later by DNA polymerase
- The nick is sealed by DNA ligase
In bacteria, how do the enzymes know which strand is the parental versus daughter strands?
The parent strand usually has methylated adenines
What does Nucleotide Excision Repair do?
Repairs damaged DNA rather than incorrectly paired ones
When is Nucleotide Excision Repair readily at play?
When cells are exposed to environmental mutagens (e.x. UV radiation)
What does UV radiation do to damage DNA?
Causes covalent bonding of two adjacent pyrimidines within DNA
* Known as Thymine Dimers
In Nucleotide Excision Repair:
What enzymes are involved in the removal of damaged nucleotides?
Endonucleases detect the improper geometry of the DNA and remove the damaged nucleotides
In Nucleotide Excision Repair:
What enzymes are involved in adding new nucleotides?
- DNA polymerase adds new nucleotides
- DNA ligase bonds the old and new nucleotides together
List:
Methods of Repiar of Mutations During Replication
- DNA Polymerase Exonuclease Activity
- DNA Mismatch Repair
