Biology 12

WHAT ARE MUTATIONS?  Changes in the nucleotide sequence of DNA  May occur in somatic cells (aren’t passed to offspring)  May occur in gametes (eggs & sperm) and be passed to offspring  The errors may occur during transcription to mRNA sequence or during DNA replication

 Exposure to mutagenic agents can increase the chance of mutations occurring  UV (ultraviolet) radiation  Chemicals  X rays

 Chromosomal  Affects multiple genes  May affect genes on separate chromosomes  Point Mutation (gene mutation)  Copying errors  Only one or a few nucleotides are affected

1. Deletion 2. Insertion 3. Substitution

 A nucleotide is left out  This shifts the reading of the DNA over one resulting in an incorrect protein AAG CCC GGC AAA AA CCC GGC AAA ← shifts over Result: AAC CCG GCA AA

MetLysLeuAlaHis Nucleotide deletion mRNA Protein MetLysPheGlyAla

 An extra nucleotide is added  This shifts the reading of the DNA over one resulting in an incorrect protein AAG CCC GGC AAA AAG ACC CGG CAA A

 Inserting or deleting one or more nucleotides changes the “reading frame” like changing a sentence  Proteins built incorrectly  Silly example:  Original:  The fat cat ate the wee rat.  Frame Shift (“a” added):  The fat caa tet hew eer at.

 One nucleotide replaces another and creates a new codon  Only affects one amino acid in the protein  Possibly could be a silent mutation AAG CCC GGC AAA AAG ACC GGC AAA

mRNA Protein MetLysPheGlyAla Base substitution MetLysPheSerAla

 Amino acid is not changed DNARNA Amino Acid CTA= GAU= Asp CTG= GAC= Asp

 mRNA = GCU ACU CAA UUC 1. Translate the mRNA above into amino acids. 2. Translate each mutated mRNA below. A. GCU ACU CGA UUC B. GCU ACG CAA UUC C. GCU ACU UCA AUU C 3. What was the result of each mutation? 4. Which would be most harmful?

 Page 263  Questions: 2, 6, 7  Page 274  Questions: 10 (a, b)