Mutations

Front 1

2 ways in which mutations can occur

Back 1

1) Spontaneous mutations (replication errors)

2) Base tautomerism

Front 2

Base Tautomerism

Back 2

When a nucleotides isometric partner replaces the intended nucleotide therefore altering the sequence.

Front 3

Effects of deaminating agents (e.g nitrous acid or sodium bisulphate)

Back 3

•Adenine--> Hypoxanthine, pairs with C not T

•Cytosine--> Uracil, pairs with A not G

•Guanine--> Xanthine, blocks DNA replication

Front 4

Alkylating agents

Back 4

Add alkyl groups to nucleotides

e.g ethylmethane sulphonate

Front 5

Intercalating agents

Back 5

Insert between base pairs

e.g ethidium bromide

Front 6

UV radiation cause mutations of what nature?

Back 6

Base dimerization

Front 7

Effect of heat on nucleotides

Back 7

Gives rise to an AP (apurinic/apyrimidinic) site via hydrolysis of glycosidic bonds

Front 8

4 main methods of mutagenic repair

Back 8

1) Direct repair

2) Excision repair

3) mismatch repair

4) nonhomologous end joining

Front 9

Direct repair

Back 9

Am enzyme corrects a nucleotide irregularity, only around 20 enzymes of this nature are known.

•Effects of some alkylating agents can be directly repaired

•Base dimers formed by UV radiation can be directly repaired

Front 10

Excision repair

Back 10

Irregular base (single) or nucleotide (multiple, sequence) is removed and the gap is filled in by DNA synthesis.

•DNA Glycosylase enzymes cleave the base + sugar

•DNA Polymerase + ligase fill in AP gap

Front 11

Difference between parent & daughter strands of DNA that assists with mismatch repair mechanism.

Back 11

Parent strands are methylated; methyl groups opposite one another on each strand. Daughter strand isn't methylated until ~ 1 minute after synthesis, this is when mismatch repairs occur.

Front 12

Mismatch repair

Back 12

Essentially like excision repair.

MutH enzyme brings opposite a methyl group, MutS binds to site with the mismatch in it. MutH cuts the DNA and the site is excised then DNA resynthesised.

Front 13

Non Homologous end joining

Back 13

Correct double stranded DNA breaks. Ku proteins attach to exposed ends, attract one another and repair the break.

Front 14

Point mutation

Back 14

One BP replaced by another.

•Transition; purine to purine (A <->G)

•Transversion; purine to pyrimidine (A or G <-> T or C)

Front 15

Inversion Mutation

Back 15

Two or more base pairs are excised and reinserted in the opposite orientation

Front 16

Synonymous and Non Synonymous mutations

Back 16

•Synonymous: no effect on the amino acid sequence so is silent

•Non-synonymous: changes the amino acid sequence, also called a missense mutation

Front 17

Nonsense mutations

Back 17

Changes an amino acid codon for a stop codon. Almost always damaging.

Front 18

Readthrough mutation

Back 18

Changes a stop codon to a codon for an amino acid (reverse of a nonsense mutation).

Front 19

Frameshift mutations

Back 19

Caused by insertions and deletions. Changes the reading frame of the sequence so all codons downstream of the mutation are changed.

Front 20

Second site reversion

Back 20

A second mutation restores the correct amino acid sequence, though the nucleotide sequence is still altered.

Front 21

Suppresion

Back 21

A mutation in a tRNA gene suppresses nonsense mutations in protein coding genes.

Front 22

Translocation

Back 22

When one part of a Chromosome becomes attached to another Chromosome following a breakage.

Can be caused by Ku proteins mismatching.