DNA mutations

Question 1

What is a Mutation?

Answer 1

 Spontaneous change in the DNA base sequence of an
organism
 Usually occurs during DNA replication and cell division
 Can occur in somatic cells (body) or germ cells (gametes

 A change or mutation in the sequence of bases in DNA can
change the triplet codon that makes up a gene.
 This can then change the amino acid sequence of the primary
structure, which can then affect the shape of the protein and
its function.
 One type is gene/point mutations

Question 2

What are somatic mutations?

Answer 2

 Are not passed on to the next generation
 Accumulate in organisms as they get older and may be one
cause of cancer

Question 3

What are germ cell mutations?

Answer 3

 Can be passed on to the zygote and new organism and
change the genome of an organism

Question 4

What types of Gene/point mutations are included?

Answer 4

Gene/point mutations include:
Substitutions – one nucleotide is replaced by another.
Insertions * – one (or more) nucleotides are added.
Deletions * – one (or more) nucleotides are removed.
Inversions – part of a gene is inverted (flipped).

Question 5

Why are mutations harmfull?

Answer 5

An alteration in the base sequence of one or two
base pairs by addition, deletion or substitution
 Occur at a single gene locus on a chromosome
altering the DNA sequence of bases and the amino
acid sequence produced
 The resulting protein shape may be altered
significantly so it does not function as required.
 Some mutations are harmful, even fatal, others
neutral and have no effec

Question 6

Explain how mutation causes Sickle cell anaemia.

Answer 6

 Sickle cell anaemia is caused by a single gene
mutation whereby thymine is replaced by adenine.
 This causes the mRNA to carry an incorrect message,
so the polypeptide contains valine instead of
glutamic acid.
 Glutamic acid is polar, so it can be found on the
outside of the globular protein as it is hydrophilic.
 However, valine is hydrophobic.
 When valine is on the outside, it makes the
heamoglobin less soluble, and the shape of the
protein changes.
 This single mutation causes sickle cells that carry
less oxygen and can block vessels.

Question 7

Explain how mutation causes cystic fibrosis

Answer 7

 Genetic disorder caused by a deletion mutation on chromosome
number 7
 Affected section shorter than the healthy section
 3 DNA bases missing
 The CF gene contains the information to make the CFTR protein.
 The CFTR protein is made up of 1480 amino acids and form a
transmembrane protein that loops across the lipid bilayer.
 For CF, many different mutations can happen to the CFTR gene
and cause the disease.
 Known mutations include:

A mutation in the ATP binding site so ATP cannot open the ion
channel.
An open ion channel that carries less Cl- ions.
The DF508 mutation where three nucleotides are deleted. This
causes the loss of phenylalanine which leads to protein
misfolding.

Question 8

What is p53 and why is it having a mutation serious?

Answer 8

 p53 is a gene that is called the ‘guardian of the
genome’.
 It encodes for a protein that checks for DNA
damage and repairs it.
 When there are mutations in p53, the protein
formed cannot function properly, thus DNA is not
repaired.
 This leads to a lot of DNA damage (from many
mutations) and the damage can lead to cancer.
 Often, p53 is checked to see if it has many
mutations because it can be used as a precursor
for cancer