Lecture 23

Question 1

mutations

Answer 1

a change in the DNA structure that can change the genetic code and cause damage

Question 2

examples of environmental factors that cause mutations

Answer 2

• UV
• radiation
• chemical agents

Question 3

what are the 3 types of point mutations?

Answer 3

All substitution mutations
- silent - same protein is made
- nonsense - no protein is made
- misuse - the wrong protein is made

Question 4

What do point mutations cause?

Answer 4

base substitutions

Question 5

What are the 2 types of substitutions caused by point mutations

Answer 5

• translation
• tranversion

Question 6

what are the two types of mutations?

Answer 6

• point mutations (one base switch)
• insertions/ deletions (one or more bases)

Question 7

How does base mismatch occur?

Answer 7

when the template strand has been damaged

Question 8

transition

Answer 8

when a purine is replaced with the other purine, causing to pair with the wrong type of pyrimidine or vice versa.
The most common substitution

Question 9

transversion

Answer 9

least common substitution, a purine is replaced with a pyrimidine or vice versa

Question 10

chemical mutagens that cause point mutations

Answer 10

• deaminating agents
• alkylating agents

Question 11

deamination

Answer 11

chemical agent, like nitrous acid, removes the NH2 and now its an O
eg. A->A* so now A-C instead of A-T (A* is basically a G)
A* is now called hypoxanthine

Question 12

what type of repair fixes deamination?

Answer 12

base pair excision

Question 13

alkylation

Answer 13

chemical agent adds a methyl/ethyl group to a purine.
eg. G->G* so now G-T instead of G-C. (G is basically a A)
G* is now called O6-alkylguanine

Question 14

what causes deamination and alkylation

Answer 14

usually chemicals in high processed food. for alkyltaion, a metabolic error can produce reactive O2

Question 15

chemical mutagens that cause insertion/deletions

Answer 15

intercalation agents - goes in between base pairs may cause another to be deleted or inserted

Question 16

what does UV damage do and what is the issue?

Answer 16

it causes adjacent Thymine pairs to bond together instead of the double bonds. called cyclobutane ring.
it is an issue because it makes it harder to separate the base pairs in order for replication

Question 17

how does UV damage get repaired

Answer 17

in plants, an enzyme called photolyase does a direct repair to fix it. Humans do not have that so instead a nucleotide excision occurs

Question 18

xeroderma pigmentosum

Answer 18

disorder when people do not have proper nucleotide excision genes. they can not go into the sun

Question 19

oxidative damage

Answer 19

metabolic error causes reactive oxygen species. Hydroxyl radicals is the worse. it is repaired by DNA glycosylases with is a base excision repair

Question 20

Direct Repair and example

Answer 20

damaged bases are repaired on site
eg. photolyase for thymine dimers or O6-alkylguanine alkyltransferase for added methyl groups.

Question 21

Base excision repair and example

Answer 21

offending base is removed and replaced
eg. glycosylase and DNA pol 1 for deamination

Question 22

Nucleotide excision repair and example

Answer 22

a whole row of nucleotides are damaged so removed and replaced
eg UV damage is removed by exinuclese and replaced by DNA pol 1

Question 23

Mismatch Repair

Answer 23

the wrong nucleotide is added during replication so the daughter strand must be identified and distinguished from the template strand and replaced.
- Enzymes MutL & MutS fid the error and identify the template strand with the methyl group on it.
- MutH cuts daughter strand from template methyl group
- portion is removed by exonuclease
- replaced by DNA pol 3

Question 24

Homologous recombination

Answer 24

repairing a break in double strand

Question 25

which is the only repair that uses DNA pol 3

Answer 25

Mismatch Repair