MUTATIONS AND CANCER Key Terms
3.8 THE CONTROL OF GENE EXPRESSION DNA replication
Spontaneous
Gene mutations MISSESTRUCH 2021
DNA base sequence
A gene mutation is the alteration of a base in the sequence of
Amino acid sequence
bases for one gene. This is likely to occur during DNA
Mutagenic agent
replication, which is during interphase in the cell cycle.
Gene mutations occur spontaneously, but
the frequency of these occurring can be
increased by certain factors which are called
mutagenic agents.
As mutations alter the gene, they can result
in a different amino acid sequence in the
encoded polypeptide.
If the amino acid sequence changes, then when the protein is modified into the tertiary structure, it
will form hydrogen and ionic bonds in different places and fold differently. This will result in a
different 3D shape, and therefore a non-functioning protein.
Alterations to the genes can result in a mutation that causes cancer.
Mutagenic agents
High energy and ionising radiation
These mutagenic agents include radiation such
as α and β particles and x-ray and gamma
rays. Ultraviolet light is not ionising, but it is
still of high enough energy to cause damage
and disrupt the structure of DNA.
Carcinogens
This is the term given to chemicals that can
alter the structure of DNA and interfere with
transcription. These include chemicals in
tobacco smoke, mustard gas and peroxides.
1
MISSESTRUCH 2021
,MUTATIONS AND CANCER Key Terms
3.8 THE CONTROL OF GENE EXPRESSION Frameshift
Gene mutations Codon
MISSESTRUCH 2021
Non-functioning protein
There are 5 different types of gene mutations:
Amino acid sequence
1.Addition
Degenerate
2.Deletion
3.Substitution
4.Inversion
5.Duplication
6.Translocation of bases
Addition
One extra base being added to the sequence.
Original: TAC TTC AGG TGG
Mutation: TAC ATT CAG GTG G
The impact of adding one base is that all subsequent codons are altered. This is known as a
frameshift. This type of mutation can be very harmful because all the altered codons could
potentially code for different amino acids and result in a very different sequence of amino acids
resulting in a non-functioning protein.
Deletion
One base is deleted from the sequence.
Original: TAC TTC AGG TGG
Mutation: TAC TCA GGT GG
This causes a frameshift to the left. This could result in a different polypeptide chain and a non-
functioning protein.
Substitution
One base has been changed for a different base, but the number of bases remains the same and
there is no frameshift. This results in only one codon changing, and due to the genetic code being
degenerate it may still code for the same amino acid and therefore have no impact.
Original: TAC TTC AGG TGG
Mutation: TAC ATC AGG TGG 2
MISSESTRUCH 2021
, MUTATIONS AND CANCER Key Terms
3.8 THE CONTROL OF GENE EXPRESSION Mutations
Mitosis
Inversion MISSESTRUCH 2021
Tumour
A section of bases detach from the DNA sequence, but when they
Benign
re-join they are inverted, so this section of code is back to front.
This results in different amino acids being coded for in this region. Malignant
Original: TAC TTC AGG TGG
Mutation: TAC GGA CTT TGG
Duplication
One particular base is duplicated at least once in the sequence. This causes a frameshift to the
right and a different sequence of amino acids are coded for.
Original: TAC TTC AGG TGG
Mutation: TAC TTT TCA GGT GG
Translocation of bases
A section of bases on one chromosome detaches and attaches to a different chromosome.
This is a substantial alteration that causes significant impacts on gene expression and therefore
the resulting phenotype.
Cancer
Cancer can result from mutations in genes that regulate
mitosis. If these genes mutate and non-functioning
proteins are made, then mitosis is not regulated. This
results in the uncontrollable division of cells and the
creation of a tumour.
Not all tumours are cancerous; they can be classified as
either benign or malignant.
3
MISSESTRUCH 2021
3.8 THE CONTROL OF GENE EXPRESSION DNA replication
Spontaneous
Gene mutations MISSESTRUCH 2021
DNA base sequence
A gene mutation is the alteration of a base in the sequence of
Amino acid sequence
bases for one gene. This is likely to occur during DNA
Mutagenic agent
replication, which is during interphase in the cell cycle.
Gene mutations occur spontaneously, but
the frequency of these occurring can be
increased by certain factors which are called
mutagenic agents.
As mutations alter the gene, they can result
in a different amino acid sequence in the
encoded polypeptide.
If the amino acid sequence changes, then when the protein is modified into the tertiary structure, it
will form hydrogen and ionic bonds in different places and fold differently. This will result in a
different 3D shape, and therefore a non-functioning protein.
Alterations to the genes can result in a mutation that causes cancer.
Mutagenic agents
High energy and ionising radiation
These mutagenic agents include radiation such
as α and β particles and x-ray and gamma
rays. Ultraviolet light is not ionising, but it is
still of high enough energy to cause damage
and disrupt the structure of DNA.
Carcinogens
This is the term given to chemicals that can
alter the structure of DNA and interfere with
transcription. These include chemicals in
tobacco smoke, mustard gas and peroxides.
1
MISSESTRUCH 2021
,MUTATIONS AND CANCER Key Terms
3.8 THE CONTROL OF GENE EXPRESSION Frameshift
Gene mutations Codon
MISSESTRUCH 2021
Non-functioning protein
There are 5 different types of gene mutations:
Amino acid sequence
1.Addition
Degenerate
2.Deletion
3.Substitution
4.Inversion
5.Duplication
6.Translocation of bases
Addition
One extra base being added to the sequence.
Original: TAC TTC AGG TGG
Mutation: TAC ATT CAG GTG G
The impact of adding one base is that all subsequent codons are altered. This is known as a
frameshift. This type of mutation can be very harmful because all the altered codons could
potentially code for different amino acids and result in a very different sequence of amino acids
resulting in a non-functioning protein.
Deletion
One base is deleted from the sequence.
Original: TAC TTC AGG TGG
Mutation: TAC TCA GGT GG
This causes a frameshift to the left. This could result in a different polypeptide chain and a non-
functioning protein.
Substitution
One base has been changed for a different base, but the number of bases remains the same and
there is no frameshift. This results in only one codon changing, and due to the genetic code being
degenerate it may still code for the same amino acid and therefore have no impact.
Original: TAC TTC AGG TGG
Mutation: TAC ATC AGG TGG 2
MISSESTRUCH 2021
, MUTATIONS AND CANCER Key Terms
3.8 THE CONTROL OF GENE EXPRESSION Mutations
Mitosis
Inversion MISSESTRUCH 2021
Tumour
A section of bases detach from the DNA sequence, but when they
Benign
re-join they are inverted, so this section of code is back to front.
This results in different amino acids being coded for in this region. Malignant
Original: TAC TTC AGG TGG
Mutation: TAC GGA CTT TGG
Duplication
One particular base is duplicated at least once in the sequence. This causes a frameshift to the
right and a different sequence of amino acids are coded for.
Original: TAC TTC AGG TGG
Mutation: TAC TTT TCA GGT GG
Translocation of bases
A section of bases on one chromosome detaches and attaches to a different chromosome.
This is a substantial alteration that causes significant impacts on gene expression and therefore
the resulting phenotype.
Cancer
Cancer can result from mutations in genes that regulate
mitosis. If these genes mutate and non-functioning
proteins are made, then mitosis is not regulated. This
results in the uncontrollable division of cells and the
creation of a tumour.
Not all tumours are cancerous; they can be classified as
either benign or malignant.
3
MISSESTRUCH 2021
