6.1 - Cellular control

Question 1

What is a mutation?

Answer 1

A random change to the genetic material.

Question 2

What is a mutagenic chemical?

Answer 2

A chemical that can induce DNA mutation.

Question 3

Will mutations associated with mitotic division (replication) and somatic mutations be passed to offspring?

Answer 3

NO.

They may be associated with the development of cancerous tumours.

Question 4

What type of mutations may be inherited by offspring?

Answer 4

Mutations that are associated meiosis and gamete formation. (as these involve the sex cells & chromosomes etc.)

Question 5

What may gene mutations affect?

Answer 5

Protein production and function

Question 6

What are the two main classes of DNA mutation?

Answer 6

1. Point mutation

2. Insertion or deletion (indel) mutation

Question 7

What is point mutation?

Answer 7

One base pair replaces (is substituted for) another

Question 8

What is indel mutation?

What might this type of mutation cause?

Answer 8

One or more nucleotides are inserted or deleted from a length of DNA.
These may cause a FRAMESHIFT

Question 9

What are the three types of point mutation?

Answer 9

• silent
• missense
• nonsense

Question 10

Why is the ‘degeneracy’ or ‘redundancy’ of the genetic code so important?

Answer 10

Because the majority of amino acids involved in protein synthesis have more than one base triplet code.

• this reduces the effect of point mutations

Question 11

What is a silent mutation?

Does it have an affect on the primary structure of the protein?

Answer 11

A point mutation involving a change to the base triplet, where that triplet still codes for the same amino acid.

• the primary structure of the protein, and therefore the secondary and tertiary structure, is not altered.

Question 12

What is a missense mutation?

Answer 12

A change to the base triplet sequence that leads to a change in the amino acid sequence in a protein.

Question 13

What effect might a missense mutation have on the protein produced?

Answer 13

The alteration to the primary structure leads to a change to the tertiary structure of the protein, altering its shape and preventing it from carrying out its usual function.

Question 14

State a condition that is caused by a missense mutation?

Answer 14

Sickle cell anaemia.
- results from a missense mutation on the sixth base triplet of the gene for the β-polypeptide chains of haemoglobin.

• the amino acid valine, instead of glutamic acid, is inserted at this position.
• this results in deoxygenated haemoglobin crystallising within erythrocytes, causing them to become sickle shaped, blocking capillaries and depriving tissues of oxygen.

Question 15

What is a nonsense mutation? Why is it so disruptive?

Answer 15

A point mutation may alter a base triplet, so that it becomes a termination (STOP) triplet.

• this results in a truncated protein that will not function.

This abnormal protein will most likely be degraded within the cell.

Question 16

State a condition which is caused by a nonsense mutation?

Answer 16

Duchenne muscular dystrophy is the result of a nonsense mutation.

Question 17

What is a frameshift?

Answer 17

If nucleotide base pairs, (not in multiples of three!!) are inserted in the gene or deleted from the gene, because the code is non-overlapping and read in groups of three bases, ALL the subsequent base triplets are altered.

Question 18

Why is a frameshift so disruptive?

Answer 18

When the mRNA from such a mutated gene is translate, the amino acid sequence after the frameshift is severely disrupted.

• the primary sequence of the protein and subsequently the tertiary structure, is much altered.
• therefore, the protein cannot carry out its normal function.
• if the protein is very abnormal, it will be rapidly degraded within the cell.

Question 19

What is thalassaemia caused by?

Answer 19

Some forms of thalassaemia, a haemoglobin disorder, result from frameshift due to the deletions of nucleotide bases.

Question 20

What do insertions or deletions of a triplet of base pairs result in?

Answer 20

The addition or loss of an amino acid, and not in a frameshift.