Mutations

Question 1

Define gene mutation

Answer 1

Random change in the base sequence of DNA.

Results in the formation of new alleles.

Question 2

List the types of mutations

Answer 2

Addition of bases;
Deletion of bases;
Substitution of a base;
Inversion of bases;
Duplication of bases / genes;
Translocation of bases / genes’
Non-disjunction of chromosomes;

Question 3

A change in the DNA base sequence may alter the [1] structure, this may alter the [2] of amino acids.

This may change the [3] of hydrogen, ionic and disulphide bonds between the [4] groups of amino acids.

This may change the [5] structure of the polypeptide.

Answer 3

[1] primary

[2] sequence

[3] position

[4] R

[5] tertiary

Question 4

List examples of mutagenic agents

Answer 4

High energy radiation e.g. x rays, gamma rays, ultraviolet light

Carcinogens e.g. benzene

Biological agents e.g. viruses

Question 5

A __________ mutation may change only one triplet code.

Answer 5

substitution

Question 6

Due to the ______________ nature of the genetic code, not all mutations result in a change to the encoded amino acid.

Answer 6

degenerate

Question 7

3 key terms for the genetic code

Answer 7

degenerate

universal

non-overlapping

Question 8

Define degenerate

Answer 8

More than one triplet / codon codes for a single amino acid

Question 9

What is meant by the universal nature of the genetic code?

Answer 9

Same 3 bases used in DNA (triplets) / mRNA (codon) code for the same amino acids in all organisms

Question 10

What is meant by the non-overlapping genetic code?

Answer 10

Each base is read only once in the triplet / codon

Question 11

Additions and [1] of bases may change the nature of all base [2] downstream from the mutation.

This results in a [3] shift.

Answer 11

[1] deletions

[2] triplets

[3] frame

Question 13

A base substitution may result in the formation of a [1] codon.

This signals to the [2] to detach from mRNA and polypeptide during translation.

This results in a [3] polypeptide.

Answer 13

[1] stop

[2] ribosome

[3] shorter

Question 13

What happens during a translocation mutation?

Answer 13

Sections of DNA bases relocate from one area of the genome to another;

e.g., between non-homologous pairs of chromosomes;

Question 13

Sickle cell disease (SCD) is a group of inherited disorders. People with SCD have sickle-shaped red blood cells. A single base substitution mutation can cause one type of SCD. This mutation causes a change in the structure of the beta polypeptide chains in haemoglobin. Explain how (3 marks).

Answer 13

1. Change in primary structure OR sequence of amino acids;
2. Change in (position) of hydrogen / ionic / disulfide bonds;
3. Alters tertiary structure;