gene mutation

Question 1

what is a gene mutation?

Answer 1

change in the base sequence of DNA

Question 2

when do mutations occur?

Answer 2

randomly during DNA replication

Question 3

what increases the rate of gene mutations?

Answer 3

mutagenic agents such as UV light, ionising radiation and carcinogens

Question 4

why do not all base substitutions change the amino acids?

Answer 4

due to the degenerate code (some amino acids can be coded for by more than one triplet)

Question 5

what arises as a result of mutations?

Answer 5

genetic diversity

Question 6

what do gene mutations mean for mRNA?

Answer 6

different codon

Question 7

what are the 3 types of mutation?

Answer 7

-substitution; one base changed for another so ONE different codon on mRNA

-deletion; one base deleted so frame shift to left

-addition; one base added so frame shift to right

Question 8

what are the 3 types of substitution and what do they mean?

Answer 8

1. silent substitution; new codon codes for same amino acid
2. mis-sense mutation; new codon codes for different amino acid
3. nonsense mutation; new codon is stop codon so doesn’t code for an amino acid

Question 9

describe how a silent substitution doesn’t affect protein coded for?

Answer 9

new codon codes for same amino acid

so same amino acid sequence in the polypeptide chain (prim structure)

H bonds, ionic bonds and disulphide bridges form in same places

same tertiary structure (3D shape)

Question 10

explain how a mis-sense mutation affects the protein coded for?

Answer 10

new codon codes for different amino acid

different amino acid sequence in polypeptide chain (prim structure)

H bonds, ionic bonds and disulphide bridges form in diff places

diff tertiary structure (3D shape)

non-functional protein (or diff function)

Question 11

explain how a nonsense mutation affects the protein coded for?

Answer 11

new codon is stop codon so doesn’t code for an amino acid

polypeptide production stops because mRNA detaches from ribosome at the stop codon

non-functional protein

Question 12

explain how addition/ deletion affects protein coded for?

Answer 12

every codon after the mutation point is different

diff amino acid sequence in the polypeptide chain (primary structure)

H bonds, ionic bonds and disulphide bridges form in different places

different tertiary structure (3D shape)

non-functional protein (or diff function)