3.8.1 - GENE MUTATIONS

Question 1

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 a single base substitution causes a change in the structure of this polypeptide (3)

Do not include details of transcription and translation in your answer

Answer 1

1. change in sequence of amino acids/primary structure;
2. change in hydrogen/ionic/disulfide bonds;
3. alters tertiary structure;

Question 2

what is a substitution mutation? (1)

Answer 2

replacement of a base by a different base (in DNA)

Question 3

suggest how a mutation can lead to the production of a protein that has one amino acid missing (2)

Answer 3

loss of 3 bases

Question 4

suggest how the production of a protein with one amino acid missing may lead to a genetic disorder (2)

Answer 4

1. change in tertiary structure/active site
2. so non-functional protein

Question 5

a mutation in the gene coding for enzyme B could lead to the production of a non-functional enzyme. explain how (3)

Answer 5

1. changes in base sequence leads to changes in amino acid sequence
2. changes in hydrogen and ionic and disulfide bonds leading to changes in tertiary structure of enzyme
3. enzyme substrate complexes cannot form

Question 6

gene mutations occur spontaneously.

during which part of the cell cycle are gene mutations most likely to occur?

suggest an explanantion for your answer (2)

Answer 6

1. interphase
2. DNA replication occurs here

Question 7

more cancer cells could be destroyed if the drug was given more frequently.

suggest why the drug was not given more frequently (2)

Answer 7

1. more/too many healthy cells killed
2. so will take time to replace them
3. person may die/have side effects

Question 8

what is a substitution mutation? (1)

Answer 8

replacement of a base by another base

Question 9

one mutation causing P was originally only found in one population in central asia. it is now found in many diferent populations across asia.

suggest how the spread of this mutation may have occurred. (1)

Answer 9

founder effect/interbreeding

Question 10

intergrase inserts the DNA copy anywhere in the DNA of a host cell. it may even insert it into the host cell’s genes.

the insertion of the DNA copy into one of the gene’s may cause the cellto make a non-functional protein.

explain how (2)

Answer 10

1. alters base sequence/causes frameshift
2. different sequence of amino acids in primary structure alters the tertiary structure