, Mutations
A mutation is a change in the sequence of bases in DNA. Protein synthesis can be disrupted if a
mutation occurs within a gene. If only 1 nucleotide is affected it is called a point mutation.
Mutations are caused by substitution, deletion or insertion of 1 or more nucleotide within a gene:
• The substitution of a single nucleotide changes the codon in which it occurs. If the new codon
codes for a different amino acid this will lead to a change in the primary structure of the
protein depending on the R group of the new amino acid. The degenerate nature of the genetic
code may mean, that the new codon codes for the same amino acid leading to no change in the
protein synthesised.
• The insertion or deletion of a nucleotide/s leads to a frameshift mutation. The triplet code
means that the sequence of bases are transcribed consecutively in non-overlapping groups of
3- this is the reading frame of a sequence of bases. Each group of 3 bases corresponds to 1
amino acid. The addition or deletion of a nucleotide moves, or shifts, the reading frame of the
sequence of bases. This will change every successive codon from the point mutation. If the
number of nucleotides changed is a multiple of 3 the reading frame will not be changed
however the protein formed will be affected as there's new/ less amino acids.
Chromosome mutation Gene mutations occur in single genes or sections of DNA whereas
chromosome mutations affect the whole chromosome or number of chromosomes within the cell
& usually occur in meiosis.
Changes in chromosome structure include:
• Deletion- A section of chromosome breaks off and is lost within the cell
• Duplication- Sections get duplicated on a chromosome
• Translocation- A section of chromosome breaks off & joins another non-homologous
chromosome
• Inversion- A section of chromosome breaks off, is reversed & then joins back onto the
chromosome
, Effects of mutations
Effects of different mutations
• Silent (neutral) mutation- No effect on the phenotype of an organism because
normally functioning proteins are still synthesised. May be due to the degenerate
nature of the genetic code, mutation codes for a new amino acid which is
chemically similar to the original or the mutated triplet codes for an amino acid not
involved with the proteins function
• Damaging- The phenotype of an organism is affected in a negative way as proteins
are no longer synthesised or are synthesised non-functional. This can interfere
with essential processes
• Beneficial- Very rarely a protein is synthesised that results in new & useful
characteristics in the phenotype. E.g. a certain mutation can cause immunity to
HIV or the ability to digest lactose.
Nonsense mutations result in a codon becoming a stop codon instead of coding for
an amino acid resulting in a shortened protein being synthesised which is normally
non-functional. These mutations usually have negative effects on phenotypes.
Missense mutations result in the incorporation of an incorrect amino acid/s into the
primary structure when the protein is synthesised. The result could be silent,
beneficial or harmful depending on the role the amino acid plays in the structure. A
conservative mutation occurs when the amino acid change leads to an amino acid
being coded for which has similar properties to the original, meaning the effect is
less severe. A non-conservative mutation is when the new amino acid coded for has
different properties to the original so is more likely to have an effect on the protein
structure.
A mutation is a change in the sequence of bases in DNA. Protein synthesis can be disrupted if a
mutation occurs within a gene. If only 1 nucleotide is affected it is called a point mutation.
Mutations are caused by substitution, deletion or insertion of 1 or more nucleotide within a gene:
• The substitution of a single nucleotide changes the codon in which it occurs. If the new codon
codes for a different amino acid this will lead to a change in the primary structure of the
protein depending on the R group of the new amino acid. The degenerate nature of the genetic
code may mean, that the new codon codes for the same amino acid leading to no change in the
protein synthesised.
• The insertion or deletion of a nucleotide/s leads to a frameshift mutation. The triplet code
means that the sequence of bases are transcribed consecutively in non-overlapping groups of
3- this is the reading frame of a sequence of bases. Each group of 3 bases corresponds to 1
amino acid. The addition or deletion of a nucleotide moves, or shifts, the reading frame of the
sequence of bases. This will change every successive codon from the point mutation. If the
number of nucleotides changed is a multiple of 3 the reading frame will not be changed
however the protein formed will be affected as there's new/ less amino acids.
Chromosome mutation Gene mutations occur in single genes or sections of DNA whereas
chromosome mutations affect the whole chromosome or number of chromosomes within the cell
& usually occur in meiosis.
Changes in chromosome structure include:
• Deletion- A section of chromosome breaks off and is lost within the cell
• Duplication- Sections get duplicated on a chromosome
• Translocation- A section of chromosome breaks off & joins another non-homologous
chromosome
• Inversion- A section of chromosome breaks off, is reversed & then joins back onto the
chromosome
, Effects of mutations
Effects of different mutations
• Silent (neutral) mutation- No effect on the phenotype of an organism because
normally functioning proteins are still synthesised. May be due to the degenerate
nature of the genetic code, mutation codes for a new amino acid which is
chemically similar to the original or the mutated triplet codes for an amino acid not
involved with the proteins function
• Damaging- The phenotype of an organism is affected in a negative way as proteins
are no longer synthesised or are synthesised non-functional. This can interfere
with essential processes
• Beneficial- Very rarely a protein is synthesised that results in new & useful
characteristics in the phenotype. E.g. a certain mutation can cause immunity to
HIV or the ability to digest lactose.
Nonsense mutations result in a codon becoming a stop codon instead of coding for
an amino acid resulting in a shortened protein being synthesised which is normally
non-functional. These mutations usually have negative effects on phenotypes.
Missense mutations result in the incorporation of an incorrect amino acid/s into the
primary structure when the protein is synthesised. The result could be silent,
beneficial or harmful depending on the role the amino acid plays in the structure. A
conservative mutation occurs when the amino acid change leads to an amino acid
being coded for which has similar properties to the original, meaning the effect is
less severe. A non-conservative mutation is when the new amino acid coded for has
different properties to the original so is more likely to have an effect on the protein
structure.
