DNA Mutations What is a mutation?

1) Change in the DNA of a gene.

2) When a cell puts its genetic code into action it is making precisely the proteins it needs for its structure and function.

3) If something changes a gene’s code words, the resulting protein may change.

4) If the protein is central to the cell’s architecture then a mutation could result in an abnormal cell.

Types of Gene Mutations

1) Substitution- can be a simple substitution in one base of the gene sequence.

For example: Original: CAC GCC ATT GCG ATGMutation: CAC GCC ATG GCG ATG

One amino acid will replace another in this type of mutation thereby altering the resulting protein.

Types of Gene Mutations

1) A Substitution is a Point Mutation

Because it occurs at only one base in the DNA Strand.

Types of Gene Mutations

Remember that DNA sequences are read in groups of three (codons) so we can use a simple

sentence to demonstrate a substitution.

Original – The Fat Cat Ate The Wee RatSubstitution – The Fat Hat Ate The Wee Rat

Where did the substitution occur?The letter “C” in Cat was changed to an “H”

Gene Mutations – Substitutions: Sickle Cell

AnemiaSickle Cell Anemia is a disease of red blood cells.

Codon for glutamic acid has been changed to code for valine because of a substitution in one codon in the gene for the protein hemoglobin.

Four hemoglobin proteins carry oxygen inside red blood cells.

The change in the amino acid causes the hemoglobin to fold abnormally causing a sickle shaped red blood cell.

Sickle Cell Anemia

The mutation affects the folding and stability of the hemoglobin protein

Frameshift Mutations-Insertions and Deletions

1) Insertions and Deletions can be point mutations

2) One or several base pairs are inserted into a gene or deleted from it.

3) This results in a shift in the reading frame or “frameshift”.

4) Therefore insertions and deletions are called “frameshift mutations”

Frameshift MutationsFrame- Shift Mutation in DNA can be demonstrated with a simple sentence.

Original – The Fat Cat Ate The Wee RatFrame Shift – The Fat CaA teT heW eeR at.

Which letter (base) was deleted?The letter “t” in CAT.

Deletions

Some times whole sections of genes are deleted.

Original – The Fat Cat Ate The Wee RatDeletion– The Fat Ate The Wee Rat

Where did the deletion occur?The word “Cat” was deleted.

Insertions (Duplications and Tandem Repeats)

Sometimes whole sections of genes are inserted.Original – The Fat Cat Ate The Wee RatInsertion– The Fat Cat Cat Ate The Wee Rat

a duplication or….

Original – The Fat Cat Ate The Wee RatInsertion– The Fat Cat Cat Cat Ate The Wee Rat….a tandem repeat (duplication continues through several

generations)

How do Mutations Occur?

1) Can occur spontaneously when copying errors occur (replication is fast and there are lots of free nucleotides around during replication.)

2) Exposure to mutagens – mutation causing agents in the environment

Types of Mutagens

1) Ultraviolet radiation in sunlight –

Skin cancer may result!!!

Types of Mutagens

2) X-rays

Types of Mutagens

3) Environmental Agents

Natural or manmade chemicals in the environment

Many carcinogens or cancer-causing agents disrupt DNA.

How are mutations fixed?

Proofreading- cells have built in mechanisms that catch and repair most of the changes that occur in DNA.

Mutations in eukaryotic cells are rare.In somatic cells any good or bad

consequences will not be passed on to offspring.

If a mutation occurs in a gamete it may be passed to the next generation.

Mutation and EvolutionA mutation and the protein made from the

mutated gene that is passed from generation to generation (inherited) can have a beneficial, harmful, or neutral effect on an organism’s ability to survive in its prevailing environment.

Therefore, gene mutations provide the foundation for change in a population of organisms – mutations provide the foundation for evolution by natural selection.

Mutation Practice

Original DNA: TAC CTC GTA AAC CCT TAA GGG ACT

Mutation 1: TAC CTC GTA CAC CCT TAA GGG ACT

Circle all that apply: Deletion, Addition, Substitution, Inversion, Duplication