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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