Mutations in DNA

• changes in the DNA sequence that can be inherited

• can have negative effects (a faulty gene for a trans-membrane protein leads to cystic fibrosis), but most mutations go unnoticed (we have two copies of each gene).

melanoma

Point Mutations

Silent Mutations have no effect on cell function (two

types) Errors that are located in intron regions - get

cut out before translation. Genetic code redundancy - a change in the

sequence may not alter the amino acid (eg. UUU and UUC both result in phenylalanine)

Point Mutations (cont.)Point Mutations (cont.)

Missense Mutation When a change in the

sequence of DNA alters a codon, resulting in a different amino acid being put in the peptide sequence.

Sickle cell anemia occurs because of a missense mutation.

Point Mutations (cont.)Point Mutations (cont.)

Nonsense Mutation A change in the DNA

sequence causes a STOP codon to be inserted in place of an amino acid codon.

The protein produced is truncated (too short).

Found in Duchenne Found in Duchenne Muscular DystrophyMuscular Dystrophy

Point Mutations (cont.)Point Mutations (cont.)

Frameshift Mutations causes the reading frame for codons to change.

Can result from deletions of nucleotides from the DNA sequence or from insertions of nucleotides into the sequence.

Either way, it shifts the reading frame in translation and results in a completely different sequence of amino acids being constructed.

Note that inserting or deleting 3 bases in the DNA wouldn’t shift the reading frame, it just adds or removes an amino acid.

Frameshift MutationsFrameshift Mutations

Major MutationsMajor Mutations