DNA Repair and Replication

Question 1

Describes DNA Polymerase exonuclease activity

Answer 1

3’ to 5’ proofreading ability.

DNA polymerase can double back and correct mistakes it made during the DNA replication process.

Question 2

Mismatch repair system

Answer 2

Removes the mismatch nucleotide pair ( and few surrounded nucleotides) once it’s detected.

After wrong nucleotide is removed DNA Polymerase goes back and add the new nucleotide and DNA ligase glues the strand.

Question 3

How does the mismatch repair system differentiates between the parent and daughter strands?

Answer 3

In prokaryotes the parent strand has more methylation.

In eukaryotes the daughter strand has single-stranded breaks.

Question 4

Base excision repair

Answer 4

For repairs that doesn’t cause distortion of the helix ( ie. alkylation, deamination, oxidation).

1. Glycosylate enzyme removes damaged nucleotide.
2. Endonuclease enzyme cleaves phosphopdiester bond.

3.DNA polymerase fills group and DNA ligase seals phosphodiester bond.

Question 5

Nucleotide Excision repair

Answer 5

Repairs for more bulky damage ( ie. thymine dimers)

1. NER endonuclease enzyme removes nucleotide
2. DNA polymerase fills nucleotide
3. DNA ligase glues backbone

Question 6

Homologous recombination

Answer 6

Used to repair double strand DNA breaks.

Used when the sister chromatid is nearby ( diploid organisms).

Question 7

Nonhomologous end joining

Answer 7

Used to repair double strand DNA breaks.

Used when sister chromatids are not present ( haploid organisms)

Question 8

How is DNA organized?

Answer 8

Wrapped around 8 histone proteins 2x ( 2 each of H1, H2A, H2B, H3, H4) this forms the nucleosome.

The nucleosomes are linked together via linker DNA.

Multiple nucleosomes and linker DNA is chromatin.

Chromatin is arranged into chromosomes where they’re stored in the nucleus.

Question 9

How is DNA attracted to histones?

Answer 9

Electrostatic attractions.

Histones are positively charged, rich in arginine and lysine.

DNA is negatively charged.

Question 10

Euchromatin v. Heterochromatin

Answer 10

Euchromatin is DNA loosely packed around histones and allows for expression of genes.

Heterochromatin is DNA tightly packed around histones and slows down the expression of genes.
Seen in telomeres and centromeres.

Question 11

Effects of Acetylation v. Methylation

Answer 11

• Acetylation is the formation of euchromatin by adding an acetyl group to lysine.
• Methylation is the formation of heterochromatin.