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13-4 Outline
I.
Do Mutations Affect Protein Synthesis?
A. Gene mutation: small-scale changes in a gene’s nucleotide sequence
B. Because 64 codes exist for 20 amino acids, some mutations won’t be
harmful
II.
Common Gene Mutations and Their Sources
A. Base-pair substitution
1. the wrong amino acid is added in place of another
2. sickle cell anemia – mutated gene on the oxygen carrying
hemoglobin distorts cell shape causing them to stick together
and disrupt circulation
B. Insertions and deletions – the addition or removal of an extra base causes
a frame shift mutation
C. Transposable elements: DNA segments move spontaneously on
chromosome which may inactivate the gene where it inserted itself
III.
Causes of Gene Mutations
A. Spontaneous generation during DNA replication when repair enzymes
don’t catch the error
B. Exposure to mutagens:
1. Electromagnetic energy - UV radiation, gamma rays, x-rays
2. Ionizing radiation from free radicals (molecular fragments with
unpaired e-)
3. Alkylating agents – natural or synthetic chemicals may
accelerate spontaneous mutations
4. Carcinogens – cause cancer
IV.
The Proof is in the Protein
A. Spontaneous mutations occur 10-4x to 10-6x per gene per generation in
eukaryotes
B. Protein mutations may be harmful, neutral or helpful effects on survival