1.6 Mutations

Question 1

What is meant by the term ‘mutation’?

Answer 1

A change in the DNA base sequence

Question 2

What are 2 examples of things that increase the risk of mutations?

Answer 2

1. Carcinogens - harmful chemicals e.g. cigarette smoke
2. Certain types of radiation - e.g. X-rays or gamma rays

Question 3

What are the 3 types of mutations?

Answer 3

1. Insertions
2. Substitutions
3. Deletions

Question 4

What is a substitution mutation?

Answer 4

A random base in the DNA base sequence is changed to a different base.

Question 5

Why do substitution mutations not always change the amino acid it usually codes for?

Answer 5

Some amino acids are coded for by more than one triplet, so substitution mutations don’t always change the amino acids in a protein

Question 6

What is an example of an amino acid that has 2 sequences of triplets it can be coded for by?

Answer 6

Tyrosine - can be coded for by TAT and TAC

Question 7

What is an insertion mutation?

Answer 7

An extra base is inserted into the sequence where it shouldn’t be

Question 8

What is the result of an insertion mutation?

Answer 8

An insertion changes the way the triplets are ‘read’, which can change the amino acids they code for. Insertions can change more than one amino acid as they have a knock-on effect on the bases further on in the sequence

Question 9

What is a deletion mutation?

Answer 9

A random base is deleted from the DNA base sequence

Question 10

What is the result of a deletion mutation?

Answer 10

Like insertions, they change the way that the base sequence is read and has knock-on effects further down the sequence as all the rest of the bases will have to move left to fill the gap

Question 11

If a mutation leads to a change in the amino acid sequence coded for by a gene, this could change the structure and function of the final protein - how could the function change?

Answer 11

The protein might work differently or it may stop working altogether

Question 12

What is an example of a protein that would be effected by a mutation?

Answer 12

Enzymes - they’re proteins that speed up chemical reactions in an organism. They have to have a specific shape for the active site to fit the substrate. A mutation in a gene that codes for an enzyme might result in the enzyme’s shape changing so much that the active site no longer fits the substrate

Question 13

A change in the function of a single protein occasionally has a big effect on phenotype - what is an example of this?

Answer 13

Cystic fibrosis - it can be caused by the deletion of just 3 bases. The gene codes for a protein that controls the movement of salt and water into and out of cells. However, the protein produced by the cystic fibrosis genetic variant doesn’t work properly. This leads to excess mucus production in the lungs and digestive system, making it hard to breathe and digest food

Question 14

Why do mutations sometimes not affect the proteins produced?

Answer 14

Mutations in coding DNA dont always change the amino acid sequence of a protein - in these cases the mutation will have no effect on protein structure or function and no effect on phenotype

Question 15

Non-coding DNA often controls the expression of coding DNA.
What does it mean for a gene to be expressed?

Answer 15

It’s turned on, so the proteins it codes for will be produced

Question 16

How can mutations in non-coding DNA affect proteins?

Answer 16

Many regions of DNA are non-coding, this means they don’t code for any amino acids. But, some of these non-coding parts switch genes on/off, so they control whether or not a gene is expressed (used to make a protein). Mutations in non-coding DNA may prevent a protein from being produced or can turn on a gene and cause a protein to be produced in the wrong place or at the wrong time.