Chapter 19 Mutations

Lecture

Mutation

Change in the genetic material (DNA)

Point Mutation

Change in 1 base pair in DNA

2 kinds of point mutations:

Base pair substitution and base pair insertions

Base pair substitutions

Replacement of base pair of DNA with a different base pair

Base pair insertions

deletions

3 types of base pair substitutions in coding regions

Missense mutation

Nonsense mutation

Silent mutation

Missense mutation

Replaces an amino acid with a different amino acid

Nonsense mutation

Replaces an amino acid with a stop codon

Silent mutation

A change in codon but no change in amino acid

Sickle cell disease: A change in primary structure

A single amino acid change (missense mutation) can affect proteins structure and function

Sickle cell disease

An inherited blood disorder results from a single amino acid substitution (glu—>val) in beta hemoglobin

Reading frame

One of the three possible ways that mRNA nucleotides can be read as triplets to specify amino acids

mRNA has 3 possible reading frames

+1 frame: start counting at the 1st base

+2 frame: start counting at the 2nd base

+3 frame: start counting at the 3rd base

Reading Frame

Codons must read in the correct reading frame for the right protein

Open reading frame (ORF)

The reading from on a mRNA that has the longest stretch of amino acids beginning with a start and ending at stop codon

Insertions and deletions

Addition or removal of DNA nucleotides

Frameshift mutation

Caused by insertion or deletion of nucleotides NOT in a multiple of 3, causing a shift in how codons are read into a different reading frame