dna mutations & repairs

Question 1

Mechanism of proofreading; used when?

Answer 1

corrects base-pair mismatches. DNA polymerase can reverse using built in 3’to5’ exonuclease to remove the new incorrect nucleotide. enzymes resume forward synthesis to add correct one.

immediately after DNA synthesis

Question 2

Mechanism of mismatch repair; used when?

Answer 2

corrects errors that escaped proof reading. mismatch repair protein/enzyme detects mispaired base, cuts new DNA strand on each side of mismatch, remove portion. repair DNA polymerase fills in gap with new DNA and DNA ligase seals.

after DNA synthesis

Question 3

Mechanism of excision repair; used when?

Answer 3

resolves nonbulky dmg (distortion of helix - bulging) to bases by removing/replacing it. nucleotide-excision repair for thymine dimers (bulky dmg caused by uv light)

Question 4

Difference between DNA damage and mutation

Answer 4

DNA dmg is single stranded change whereas mutation is double stranded change.

Question 5

Types of DNA damage and their sources (both endogenous and exogenous)

Answer 5

exogenous: uv light, chemicals, ionzing radiation generates ROS
endogenous: metabolism (ROS), cell respiration (reactive electrons travel singularly), replication error

Question 6

Role of UV, ionizing radiation and ROS in mutagenesis

Answer 6

uv light causes thymine dimers - distortion in DNA.

ionizing radiation splits water molecules in cells apart - ROS will dmg DNA to reach stability leading to double stranded breaks.

Question 7

antioxidants

Answer 7

gets rid of ROS - free radicals which may be a factor in diseases.

Question 8

mechanism of photolyase

Answer 8

repairs thymine dimers (NOT IN HUMANS) caused by uvlight. it needs white light to be activated.

Question 9

mechanism of non-homologous end joining

Answer 9

pieces DNA back together but generally introduces errors as no template is being used.

repairs double stranded breaks (caused by ROS).

Question 10

Relative distribution of various components of genome sequence - essential and coding

Answer 10

10% essential DNA. out of that 10%, 2% is used for coding

Question 11

SNP mutation

Answer 11

single base pair nucleotide difference in DNA sequence (aka substitution).

usually has no effect on health/development but some can

Question 12

InDel mutation

Answer 12

insertion/deletion

due to DNA polymerase slippage. forward slippage (template strand): deletion. backward slippage (in coding strand): insertion.

Question 13

The different chemical forms of the 4 nitrogenous bases (do not need to memorize preferential pairings of the 4 tautomers)

Answer 13

G & T = keto (before) and enol (after)

A & C = amino (before) and imino (after)

Question 14

The role of tautomeric shifts in mutagenesis

Answer 14

causes DNA dmg (NOT mismatch). causes nucleotide to pair with one which is not their pair. could lead to mutation

Question 15

Difference between transition and transversion mutations

Answer 15

transitions are purine to purine & pyrimidine to pyrimidine.

transversions are purine to pyrimidine etc.

Question 16

How transposable elements were discovered

Answer 16

Barbara McClintok discovered it bc she wondered why kernals (in corn) are diff colours in diff areas. she experiments on corn/maize.

Question 17

How diseases are multifactorial

Answer 17

many SNPs associated with increased risks for heart disease.

7-% of cystic fibrosis caused by one mutation in CFTR gene (2 nucleotides deleted)