The control of gene expression

Question 1

Define mutation.

Answer 1

A permanent, random change in the nucleotide sequence of DNA.

Question 2

Mutations can be caused by errors during what process?

Answer 2

DNA replication.

Question 3

What are mutagens?

Answer 3

Agents that are capable of increasing the rate of genetic mutation.

Question 4

What is a substitution mutation?

Answer 4

Where one or more bases are swapped with another.

Question 5

What is a deletion mutation?

Answer 5

Where one or more bases are removed from the sequence, causing a frame shift.

Question 6

What is an addition mutation?

Answer 6

Where one or more bases are added to the sequence, causing a frame shift.

Question 7

What is a duplication mutation?

Answer 7

Where one or more bases are repeated, causing a frame shift.

Question 8

What is an inversion mutation?

Answer 8

Where a sequence of bases is reversed, not causing a frame shift.

Question 9

What is a translocation mutation?

Answer 9

Where a sequence of bases is moved from one location in the genome to another. This could be movement within the same chromosome or movement to a different chromosome.

Question 10

The order of DNA bases in a gene determines…

Answer 10

…the sequence of amino acids in a particular polypeptide. If a mutation occurs in a gene, the sequence of amino acids in the polypeptide that it codes for could be changed.

Question 11

What effect would a mutation have on the functionality of an enzyme if that mutation affects its final 3D shape?

Answer 11

If the shape of the active site of the enzyme is altered, there’s the possibility that the substrate may no longer be complementary in shape to the active site and so an enzyme-substrate complex won’t be able to form. If the substrate can no longer bind to the enzyme, the enzyme won’t be able to catalyse the reaction.

Question 12

What are hereditary mutations?

Answer 12

A gamete containing a mutation for a genetic disorder or a type of cancer is fertilised, so the mutation is present in the new foetus.

Question 13

Beneficial hereditary mutations allow for…

Answer 13

…Evolution.

Question 14

Why can the genetic code be described as degenerate?

Answer 14

There are more possible base triplet combinations (64) than there are amino acids (20), therefore some amino acids are coded for by more than 1 base triplet.

Question 15

What the degeneracy of the genetic code mean for mutations and their effect?

Answer 15

Not all mutations will always result in a change in the amino acid sequence of the polypeptide. A substitution could give a codon that codes for the same amino acid.

Question 16

What is a silent mutation?

Answer 16

Where a mutation has no effect on the amino acid sequence and therefore doesn’t change the polypeptide.

Question 17

Which types of mutation almost always change the sequence of amino acids of a polypeptide?

Answer 17

Addition, deletion and duplication mutations. These mutations change the number of bases in the sequence.

Question 18

What is the term for the base triplets that follow on from the point of mutation?

Answer 18

Downstream.

Question 19

Name some mutagenic agents.

Answer 19

Ultraviolet radiation
X-ray radiation
Gamma radiation
Alpha radiation
Beta radiation

Question 20

How can mutagens act as a base?

Answer 20

Chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA.
An example is 5-bromouracil. This is a base analog that can substitute for thymine and pair with guanine (instead of adenine), causing a substitution mutations in the new DNA.

Question 21

How can mutagens act as a base?

Answer 21

Some chemicals can delete or alter bases.
For example, alkylating agents can add an alkyl group to guanine, which changes the structure so that it pairs with thymine instead of cytosine.

Question 22

How can mutagens change the structure of DNA?

Answer 22

Some types of radiation can change the structure of DNA, which causes problems during DNA replication.
For example, UV radiation can cause adjacent thymine bases to pair up together.