How might gene mutations arise?

Spontaneously, for example by errors during DNA replication.

Name the six types of gene mutation.

Substitution, addition, deletion, inversion, duplication and translocation.

What is an inversion?

A group of bases cut out and rejoined in the reverse order.

What is a translocation?

A group of bases moves from one location to another, in the same or a different chromosome.

Name a mutagenic agent.

Ultraviolet light, ionising radiation or chemicals in tobacco smoke.

What does a mutagenic agent do?

It increases the rate of mutation.

What does it mean to say the genetic code is degenerate?

Most amino acids are coded for by more than one triplet.

Why does a substitution not always change the amino acid?

The new triplet may code for the same amino acid because the code is degenerate.

What is a frameshift?

A change in all triplets downstream of a deletion or addition, because the reading frame has shifted.

Which mutations cause a frameshift?

Additions or deletions of bases in numbers that are not multiples of three.

Why can a different amino acid change protein function?

It can change the bonds, and so the tertiary structure and shape of the active or binding site.

Effect of a substitution that creates a stop codon?

Translation ends early, giving a shorter, usually non-functional polypeptide.

Mutations and their effectsAQA A-Level Biology: Flashcards

Card 1 of 140 of 14 known

Question

What is a gene mutation?

Tap or press Space to reveal

Tap card or press Space to flip

See all 14 cards

What is a gene mutation?: A change in the base sequence of DNA.
How might gene mutations arise?: Spontaneously, for example by errors during DNA replication.
Name the six types of gene mutation.: Substitution, addition, deletion, inversion, duplication and translocation.
What is a substitution?: One base replaced by another.
What is an inversion?: A group of bases cut out and rejoined in the reverse order.
What is a translocation?: A group of bases moves from one location to another, in the same or a different chromosome.
Name a mutagenic agent.: Ultraviolet light, ionising radiation or chemicals in tobacco smoke.
What does a mutagenic agent do?: It increases the rate of mutation.
What does it mean to say the genetic code is degenerate?: Most amino acids are coded for by more than one triplet.
Why does a substitution not always change the amino acid?: The new triplet may code for the same amino acid because the code is degenerate.
What is a frameshift?: A change in all triplets downstream of a deletion or addition, because the reading frame has shifted.
Which mutations cause a frameshift?: Additions or deletions of bases in numbers that are not multiples of three.
Why can a different amino acid change protein function?: It can change the bonds, and so the tertiary structure and shape of the active or binding site.
Effect of a substitution that creates a stop codon?: Translation ends early, giving a shorter, usually non-functional polypeptide.

Exam questions on Mutations and their effects

A short section of the coding strand of a gene reads ATG GAA CTT AAG GGC and codes for the amino acids methionine, glutamic acid, leucine, lysine and glycine. A mutation changes the third base of the second triplet from A to G, giving GAG, which also codes for glutamic acid. A different mutation changes the same triplet from GAA to TAA.
Explain the effect on the polypeptide of the mutation that changes GAA to TAA.2 marks
The coding strand of part of a gene reads CAT GAT TCC AAG and codes for four amino acids. A mutation deletes the first G of the second triplet.
Explain why a deletion of one base usually has a greater effect on a polypeptide than a substitution of one base.2 marks
A researcher grew a culture of bacteria and counted the number of cells that had mutated to become resistant to an antibiotic. In an untreated culture there were 3 resistant cells per million cells. In a culture exposed to ultraviolet light there were 450 resistant cells per million cells. The resistance was caused by a single-base change in a gene coding for a bacterial protein to which the antibiotic normally binds.
Explain the results of the researcher's experiment.3 marks

See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).