The effect of gene mutations on polypeptides

Question 1

Most mutations do not alter the polypeptide or only alter it slightly so that

Answer 1

its appearance or function is not changed

Question 2

However, a small number of mutations code for a significantly altered polypeptide with a different shape
This may affect the ability of the protein to perform

Answer 2

function

If the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site

A structural protein (like collagen) may lose its strength if its shape changes

Question 3

There are natural mechanisms that take place within cells to ensure the accuracy of DNA replication
These mechanisms involve

Answer 3

proofreading and repairing damaged DNA

Question 4

mechanisms involve proofreading and repairing damaged DNA

When the mutation rate of a cell rises to above a normal (usually low) rate then these mechanisms have become ineffective

Mutagenic agents are

Answer 4

Mutagenic agents are environmental factors that increase the mutation rate of cells
Examples include:

Question 5

mutagenic agents example

Answer 5

High-energy radiation such as UV light
Ionising radiation such as X rays
Toxic chemicals such as peroxides

Question 6

Exam Tip
A silent mutation is a change in the nucleotide sequence that results in the same amino acid sequence.This is possible because some amino acids can be coded for by up to four different triplet codon sequences.Silent mutations are often a change in the 2nd or 3rd base in the codon, rather than the first.For example, valine is coded for by four different triplet codon sequences (GUU, GUC, GUA and GUG) – therefore, as long as the first two nucleotides in the codon are guanine and uracil valine will be inserted into the polypeptide.