DNA mutations

Question 1

Two types of DNA mutation causes

Answer 1

Spontaneous and induced

Question 2

Examples of spontaneous mutations

Answer 2

Chemical properties of nucleic acids, problems during replication or cell division

Question 3

Examples of induced mutations

Answer 3

Radiation, chemicals

Question 4

Mutation broad definition

Answer 4

Changes in the DNA sequence

Question 5

Two types of DNA mutations

Answer 5

Point- one base pair altered

structural- include large sections of the DNA, often chromosomes

Question 6

Different types of point mutations explained

Answer 6

1. Substitution of a base
   - transition when a purine or pyrimidine base is exchanged for the same type
   - transversion when a purine or pyrimidine base is exchanged for a different type
2. addition or loss of a base (insertion or deletion)
   - create a frame shift and a new open reading frame of the gene

Question 7

Missense mutation definition + explained

Answer 7

Substitution of a base that produces a new triplet that codes for a new amino acid that produces a functional alteration in the protein, which is lethal if homozygous.

Question 8

Nonsense mutation definition + explained

Answer 8

Change, addition or subtraction, of a base produces a termination codon and protein synthesis stops to produce an incomplete protein chain.

Question 9

How may the mutations arise?

Answer 9

• deamination of cytosine, producing uracil
• depurination, producing a pyrimidine
• an error in replication not correctly proofread by DNA polymerase
• Polymerase slippage, repeating a section of the template

Question 10

Mutagen definition

Answer 10

Factors involved in increasing the basal mutation rate by directly modifying the DNA

Question 11

Mutagenic agent definition + examples

Answer 11

Numerous physical and chemical compounds that act as mutagens

Ionising radiation- X ray, gamma radiation, UV light. Tobacco smoke, mustard gas, nitrous acid (dominates)

Question 12

What does UV damage cause?

Answer 12

Dimerisation of thymine- two thymines are covalently linked affecting the structure of DNA which affects replication.

Question 13

Different repair systems explained

Answer 13

Direct repair- damaged nucleotide. Alkylating agents transfer methyl group to base which is then transferred to repair enzyme

excision repair- damaged nucleotide. C-U deamination nucleotides. DNA glycosylases cut site

mismatch repair- thymidine dimers excised and resynthesised

Question 14

What is a silent mutation?

Answer 14

Base substituted for another, however triplet still codes for same amino acid so no change to protein structure.

Question 15

3 consequences of mutations for protein production

Answer 15

1. new protein formed with gained function
2. new protein formed with loss of function
3. produces abnormal protein that interferes with normal production of the other allele

Question 16

What is a transponson?

Answer 16

DNA segments that have the ability to jump or move places in the genome to another, either within same chromosomes or between different chromosomes

Question 17

synonymous vs non synonymous mutations

Answer 17

synonymous mutations result in a slight alteration that does no change anything

non synonymous mutations result in a change in amino acid