BFCP1 S10

S10: DNA Mutation and Repair

Endogenous vs exogenous DNA damage

Endogenous: within the cell, like DNA pol error

Exogenous: external factors, like UV radiation

T/F: most DNA damage is repaired after replication

F - before replication

At which part of interphase do mutagens cause the most damage and why?

S, because it has lower fidelity repair mechanisms than G1/G2

Basal mutation rate

Mutation rate caused by endogenous factors

Tautomeric shifts (and what causes it)

SPONTANEOUS change from one base form to another

Ex: the enol form of T pairs with G, the imino form of A pairs with C

T/F: ionizing radiation penetration is strong enough to affect somatic and germ line cells

T

Ex: X-rays

If one DNA strand is damaged, ______ is used.

If both DNA strands are damaged, ______ is used.

If one DNA strand is damaged, the other strand is used.

If both DNA strands are damaged, the sister chromatid is used.

___/_____ DNA mutations go unrepaired

1/1000 - high fidelity

What are the 4 R’s of DNA repair?

1. Recognize: the damaged DNA strand

2. Remove: the damage

3. Repair: using DNA pol

4. Religate: using DNA ligase

What would be the cause of DNA repair mechanisms not working properly?*

Due to mutations in the GENES ENCODING the protein responsible for repair

Mismatch repair

Repair of Watson-Crick mismatches (aka if A isn’t bound to T or C isn’t bound to G)

Mismatch repair mechanism

1. Nick the damaged DNA

2. Repair proteins remove part of the strand

3. DNA pol and ligase repair

Colon cancer is caused by mutations in genes that code for ______ repair proteins.

mismatch

Base excision repair

Mutations in the base itself or a missing base

Depurination, depyrimidation, and deaminations are all examples of which DNA damage?

Base excision repair

Define: depurination and deamination

Depurination: complete loss of A or G from a nucleotide

Deamination: cytosine loses its amine and turns into uracil

What is the rarest form of base excision damage?

Depyrimidation

Base excision repair mechanism for deamination

1. nucleotide glycocylase removes uracil

2. AP endonuclease recognizes the missing base and cuts the backbone

3. DNA pol and DNA ligase repair

Nucelotide-glycocylase role in base excision repair

Removal of the wrong base

AP endonuclease role in base excision repair

Recognizes missing base and makes a nick on the backbone

Base excision repair mechanism for depurination

1. AP endonuclease recognizes the missing base and cuts the backbone

2. DNA pol and DNA ligase repair

Nucleotide excision repair removes which type of damage?

Removes UV and chemically induced DNA damage

What can UV radiation cause?

What repair mechanism is necessary for this?

Pyrimidine dimers in adjacent bases

Nucleotide excision repair

Nucleotide excision repair mechanism

1. AP endonuclease recognizes the missing base and removes the dimerized nucleotides

2. DNA pol and DNA ligase repair

Xeroderma pigmentosum is caused by mutations in genes that encode _______ repair proteins. This causes them to not be able to _________.

nucleotide

repair thymine dimers → more susceptible to skin cancer

Homologous recombination and non-homologous end joining are examples of which repair?

ds DNA repair

ds DNA repair fixes _______.

damage to both strands

Homologous recombination vs non-homologous end joining

Homologous recombination: replacing the affected strands

Non-homologous end joining: removing the affected strands and connecting the rest together

Which is more common: homologous recombination or non-homologous end joining

non-homologous end joining

Mutations in the _____ and ______ genes increase risk of breast cancer and play a role in _____ repair (specifically, ______).

Mutations in the BRCA1 and BRCA2 genes increase risk of breast cancer and play a role in ds DNA repair (specifically, homologous recombination).

Homologous recombination repair mechanism:

1. ____ break

2. Exonuclease

3. Strand invasion

4. DNA pol + ligase

1. ds DNA break

2. Exonuclease degrades the 5’ end of both strands

3. Strand invasion: broken strand invades sister chromatid

4. DNA pol uses the sister chromatid as a template to rebuild the strands

5. DNA ligase seals