Gene Mutation

Question 1

What is a mutation?

Answer 1

Any change to the base sequence of DNA.
Mutations in body cells are not passed on to the next generation.
Mutations occurring during the formations of gametes may be inherited.

Question 2

How can mutations be caused?

Answer 2

Mutations can be caused by errors during DNA replication.
or
mutagenic agents.

Question 3

Name three types of mutation.

Answer 3

Substitution
Deletion
Addition

Question 4

What is substitution mutation?

Answer 4

One base is substituted with another, e.g ATGCCT because ATTCCT.

Question 5

What is deletion mutation?

Answer 5

One base is deleted, e.g ATGCCT becomes ATCCT.

Question 6

What is addition mutation?

Answer 6

One or more bases are added in, e.g ATGCCT becomes ATGACCT.

Question 7

What determines the order of amino acids in a particular protein?

Answer 7

The order of DNA bases in a gene.

Question 8

What can happen to a protein if the sequence of amino acids are altered?

Answer 8

It may affect the protein’s tertiary structure so the protein might not function the way it’s supposed to.

Question 9

Do all mutations affect the order of amino acids in a protein?

Answer 9

No- the degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet meaning not all substitution mutations will result in a change to the amino acid sequence of the protein.

Question 10

Why does deleting or inserting a base always lead to changes in the amino acid sequence?

Answer 10

Deleting or inserting a base will change the number of bases present, which will cause a shift in all the base triplets after it.

Question 11

What are mutagenic agents?

Answer 11

Things that cause an increase in the rate of mutations.

For example, UV radiation, ionising radiation, some chemicals and some viruses.

Question 12

How do mutagenic agents increase the rate of mutations?

Answer 12

1. Acting as a base- chemicals called base analogs can substitute for a base during DNA replication.
2. Altering bases- some chemicals can delete or alter bases.
3. Changing the structure of DNA- causes problems during DNA replication.

Question 13

What are hereditary mutations?

Answer 13

You inherit them from your parents.

They are present in the gametes, so if a gamete is fertilised the fetus will have the mutation.

Question 14

What are acquired mutations?

Answer 14

You develop them during your lifetime.

Acquired mutations occur in individual cells after fertilisation.

Question 15

When might a mutation occur spontaneously?

Answer 15

During DNA replication.

Question 16

Substitution mutation: depending on which new base is substituted for the original base there are three possible consequences…

Answer 16

A nonsense mutation
A mis-sense mutation
A silent mutation

Question 17

Substitution mutation: What is a nonsense mutation?

Answer 17

Occurs if the base change results in the formation of one of the three stop codons that mark the end of a polypeptide chain.
e.g GTC -> ATC means that it is transcribed as UAG in mRNA (a stop codon)- polypeptide chain formation would stop.

Question 18

Substitution mutation: What is a mis-sense mutation?

Answer 18

Arises when the base change results in a different amino acid being coded for.

Question 19

Substitution mutation: What is a silent mutation?

Answer 19

Occurs when the substituted base has no effect of the function because they code for the same amino acid

Question 20

What are proto-oncogenes?

Answer 20

Genes that stimulate cell division.

Question 21

What are tumour supressor genes?

Answer 21

Genes that slow cell division.

Question 22

How can proto-oncogenes affect cell division?

Answer 22

The receptor protein on the cell surface membrane can be permanently activated, so that cell division is switched on even in the absence of growth factors.
The oncogene may code for a growth factor that is then produced in excessive amounts, again stimulating excessive cell division.

Question 23

Explain why a deletion gene is more likely to result in a change to an organism than a substitution gene mutation?

Answer 23

In a deletion all the codons after are affected (frame shift).
In substitution only a single codon (therefore a single amino acid) will be affected.