mutations

Question 1

what is a gene mutation?

Answer 1

a change in the base sequence of DNA.

Question 2

what is a mutagenic agent?

Answer 2

a factor that increases rate of gene mutation e.g UV light, x-rays, viruses.

Question 3

what are the ways in which DNA bases change?

Answer 3

substitution
deletion
insertion

Question 4

how are mutations passed on?

Answer 4

through gametes (mutations in normal body cells are not passed on)

Question 5

what are the three types of substitution?

Answer 5

silent mutation
non-sense mutation
mis-sense mutation

Question 6

what is silent mutation?

Answer 6

when the substituted base is different but codes for the same amino acid - no change in the polypeptide that is formed.

Question 7

what is non-sense mutation?

Answer 7

the base change results in the formation of a stop codon so the production of polypeptide would be stopped prematurely - the protein would be different and not function.

Question 8

what is mis-sense mutation?

Answer 8

the base change results in a different amino acid being coded for which could result in a slightly different polypeptide.

Question 9

what is deletion?

Answer 9

a nucleotide is lost from the normal DNA sequence.

Question 10

what is insertion?

Answer 10

addition of another nucleotide.

Question 11

explain the possible effects of a substitution mutation.

Answer 11

• DNA base is replaced by a different base.
• this changes one triplet so changes one mRNA codon.
• so one amino acid in polypeptide changes.

Question 12

explain the possible effects of a deletion mutation.

Answer 12

• one nucleotide is removed from the DNA sequence.
• which changes the sequence of DNA triplets, mRNA codons, amino acids in primary structure of polypeptide etc.
• changes the position of bonds in tertiary structure.
• changes tertiary structure.

Question 13

describe the frame shift (mutation)

Answer 13

it’s caused by an insertion or deletion mutation and can affect the groups of codons being read in the reading frame.

Question 14

explain how a mutation can lead to the production of a non-functional protein/enzyme.

Answer 14

• changes the base sequence in DNA that codes for protein, so changes the sequence of codons on mRNA.
• this changes the sequence of amino acids in a polypeptide.
• so changes the position of hydrogen/ionic/disulphide bonds.
• which changes the tertiary structure of protein.
• this means it can change the shape of active site so the substrate can no longer bind to it, so fewer enzyme substrate complexes form.