L13: Gene Mutations

Question 1

What is a mutation?

Answer 1

Change in a DNA sequence

Question 2

3 causes of mutations

Answer 2

1) DNA replication errors
2) Spontaneous mutations
3) Chemicals & radiations

Question 3

Define somatic mutations

Answer 3

Occur in body cells (not gametes), not inherited

Question 4

Define germ-line mutations

Answer 4

Occur in gametes (sperm/egg), can be inherited

Question 5

3 types of base-pair substitutions

Answer 5

1) Silent mutation
2) Missense mutation
3) Nonsense mutation

Question 6

Define silent mutation

Answer 6

Base-pair change but DOES NOT alter amino acid

Question 7

Define missense mutation

Answer 7

Changes a codon, resulting in a different amino acid in a protein

Question 8

Define nonsense mutation

Answer 8

Changes a codon into a stop codon, leading to premature termination of translation

Question 9

2 types of missense mutation substitution

Answer 9

1) Conservative substitution
2) Non-conservative substitution

Question 10

Define conservative substitution

Answer 10

Substitutes chemically similar amino acid

Question 11

Define non-conservative substitution

Answer 11

New amino acid chemically different, alter protein function

Question 12

When does a frameshift mutation occur?

Answer 12

When 1 or more nucleotides are inserted/deleted, altering reading frame of gene
- Changes all downstream codons

Question 13

What do regulatory mutations affect?

Answer 13

Promotors/regulatory protein binding sites

Question 14

What is induced mutation?

Answer 14

Caused by mutagens (environmental agents e.g chemicals)

Question 15

What is spontaneous mutations?

Answer 15

Occurs without known mutagens, due to DNA replication errors

Question 16

2 effects of regulatory mutations and their effects

Answer 16

1) Reduced Transcription: Mutations in promotors can reduce/abolish transcription

2) Enhanced Transcription: Some mutations increase transcription levels

Question 17

What causes trinucleotide repeat disorders?

Answer 17

DNA pol slipping during replication, increasing no. of repeats in genes

Question 18

What are tautomeric shifts?

Answer 18

Alternative structures of nucleotide bases

e.g amino -> imino
keto -> enol

Question 19

What can tautomeric shifts lead to?

Answer 19

Base-pair mismatches during DNA replication, causing mutations

Question 20

What are transposable elemtns?

Answer 20

DNA sequences that can move within the genome of all prokaryotes/eukaryotes

Question 21

2 types of transposable elements

Answer 21

1) DNA transposons
2) Retrotransposons

Question 22

How do DNA transposons and Retrotransposons move?

Answer 22

DNA: Via transposase protein
Retro: Via an RNA intermediate & reverse transcriptase

Question 23

How can transposable elements cause mutation?

Answer 23

By inserting into a gene & causing an insertion mutation

Question 24

Describe the structure of DNA transposons?

Answer 24

Contain a transposase gene, which is bordered by inverted repeats

Question 25

Function of transposase

Answer 25

Cuts DNA & inserts the IS element into a new location

Question 26

Types of induced mutagens

Answer 26

1)** Base analogs: **Mimic nucleotides 2) **Alkylating agents:** Adds methyl/ethyl groups to bases 3) **Intercalating agents:** Insert between base pairs, causing frameshift

Question 27

3 types of DNA repair mechanisms

Answer 27

1) Photoreactivation Repair 2) Base Excision Repair 3) Nucleotide Excision Repair

Question 28

Describe photoreactivation repair

Answer 28

Repairs thymine dimers caused by UV light - Enzyme photolyase cleaves dimer bond

Question 29

Describe base excision repair

Answer 29

Removes damaged bases & replaces with correct ones

Question 30

Describe nucleotide excision repair

Answer 30

Repairs bulky DNA lesions by excising a segment of DNA & synthesising a new strand