Gene Mutations

Gene

Section of DNA; coding for a polypeptide

Polypeptide

Chain of amino acids joined by peptide bonds

Genome

All genetic material of an organism, including genes and non coding DNA

Protein

1 or more polypeptide chains folded

Histone

The protein DNA wraps around to form chromatin. Allows DNA to be more compactly packaged

Transcription

Process of copying DNA base sequence into mRNA

Translation

Process of using mRNA base sequence to produce a specific polypeptide chain

What is a mutation?

Change to the DNA bases/nucleotides

Chromosomal Mutations

These affect the whole chromosome/number of chromosomes within a cell

Point mutation

A type of chromosome mutation in which a single nucleotide in the DNA sequence is altered

Gene Mutations

These are changes to the base sequence of genes in DNA

Types of Gene Mutation

- Substitution

- Insertion

- Deletion

Substitution:

One or more bases are swapped for others, like A to G

3 types of Substitution Mutation:

- Mis-sense

- Nonsense

- Silent

1) Mis-sense

A substitution causes a different amino acid to be coded for

This change to the primary structure may change the tertiary structure and overall 3D shape of the protein

If this happens, then the functionality of the protein is likely to change.

2) Non-sense

One base is substituted with another and this causes a STOP codon to be created. This will produce a shorter polypeptide that is likely to fold differently. If this happens, then the functionality of the protein is likely to change.

3) Silent

A substitution occurs that has NO effect on the amino acid coded for due to the degenerate nature of the code

Insertion:

One or more bases are added into the sequence of the gene

Deletion:

One or more bases are removed from the sequence of the gene

Insertions & deletions cause:

a frameshift

- Every codon after the mutation is affected

- The protein will have a different sequence of amino acids

- And a different tertiary structure

If one or more bases are removed or added to the DNA base sequence of a gene, then...

...a frameshift mutation will occur. The reading frame will now line up different triplets after the point of mutation.

Whole Chromosome Mutation Example

Down Syndrome

Deletions in Chromosomal Mutations

A section of chromosome breaks off and is lost within the cell

Duplications in Chromosomal Mutations

Sections of chromosomes (or entire chromosomes) are duplicated

Translocations in Chromosomal Mutations

A section of one chromosome breaks off and joins another non-homologous chromosome

Inversions in Chromosomal Mutations

A section of one chromosome breaks off, is reversed, and joins back to the chromosome