Genes

Question 1

Mis-sense mutation

Answer 1

Base change results in a different amino acid being coded for.
The polypeptide differs by one amino acid. The significance of this depends on the role of the amino acid.
(If it is important in forming the bonds that determine the tertiary structure of then final protein, then the replacement amino acids may not form the same bonds. If the protein is an enzyme, the active site may no longer fit the substrate and catalyse reactions)

Question 2

Silent mutation

Answer 2

Substituted base, although different, still codes for the same amino acid as before due to the degenerate nature of the genetic code. The mutation has no effect.

Question 3

Base deletion

Answer 3

A nucleotide is lost from the normal DNA sequence.
The genetic code is read in units of 3 (triplets) so a frame shift occurs. The gene iOS now read in the wrong 3-base groups.
Worse when it happens near the start of the sequence

Question 4

Proto-oncogenes

Answer 4

Stimulate cell decision

Question 5

Oncogenes

Answer 5

Affect cell division by…

1. permanently activating the receptor protein on the cell-surface membrane so cell division takes place even in the absence of growth factors
2. coding for a growth factor that us then produced in excessive amounts, stimulating excessive cell division

Question 6

Tumour suppressor genes

Answer 6

Slow/inhibit cell decision

Question 7

Nonsense mutation

Answer 7

The base change results in the formation of a stop codon, marking the end of a polypeptide chain.
The production of the polypeptide is stopped prematurely.