MGD S9 - Mutagenesis

Question 1

Define mutation

Answer 1

Change in the nucleic sequence caused by the addition, removal or rearrangement of one or more nucleotides

Question 2

Name the types of point mutation and their effect

Answer 2

Silent - no change in the amino acid translated

Missence - Substitution of a base resulting in a replacement of one amino acid for another

Non-sense - substitution of a base changing the amino acid specified to a stop codon

Frameshift mutation - Addition or subtraction of nucleotides not in multiples of 3

Question 3

What is the cause of a frameshift mutation?

Answer 3

Addition or deletions of bases not in multiples of three

Question 4

Why can a silent mutations still have serious consequences?

Answer 4

Substitution of a base may occur in a binding site, promoter sequence or splice site on DNA

Question 5

Explain two ways that spontaneous mutations can occur?

Answer 5

Tautomeric shift - nucleotides briefly change to tautomeric form and so behave as altered template bases in replication

DNA strand slippage - template or new strand loops out during replication causing imperfect base pairing

Question 6

Name two chemicals that can induce mutation

Answer 6

Nitrous acid, Ethyl methane sulphonate (EMS), IQ

Question 7

Name two sources of radiation that can induce mutation

Answer 7

X-rays, radon gas in the environment

Question 8

Why is some ultraviolet B required by humans at healthy levels?

Answer 8

Needed to induce vitamin D production in the skin Too much UVB exposure can cause sun burn and some forms of skin cancer

Question 9

Name the mechanisms of DNA repair

Answer 9

1) Excision repair - nucleotide excision for UV damage, base excision for oxidative damage
2) Nucleotide mismatch repair - proof reading
3) p53 - monitors and promotes apoptosis when sever damage occurs

Question 10

What are the mechanisms by which cancer genes become homozygous in order for tumour formation to be initiated?

Answer 10

1) Loss of chromosome with wild type allele
2) Deletion of wild type allele on chromosome
3) Point mutation on chromosome which originally held wild type allele
4) Mitotic Recombination- rare

Question 11

Name two disease that can be identified by genetic tests and the tests used

Answer 11

Sickle cell anaemia- Southern blotting

Cystic fibrosis- PCR and southern blotting/DNA sequencing

Question 12

Base substitutions can either be _______ or ______

Answer 12

Transition or transversion

Question 13

What is a transition point mutation?

Answer 13

Purine substituted with a purine OR pyramidine substituted with pyramidine

Question 14

What is a transversion point mutation?

Answer 14

purine to pyramidine or vice versa

Question 15

What is an oncogene?

Answer 15

Genes normally involved in control of cell growth (proto-oncogenes) but has transformed a cell into a tumour cell (oncogenes)