mutations
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MUTATIONSBiology 12
JOKE OF THE DAY:
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
CAUSES: Exposure to mutagenic agents can
increase the chance of mutations occurring UV (ultraviolet) radiation Chemicals X rays
TYPES OF MUTATIONS Chromosomal
Affects multiple genes May affect genes on separate
chromosomes
Point Mutation (gene mutation) Copying errors Only one or a few nucleotides are affected
TYPES OF POINT MUTATIONS:1. Deletion2. Insertion3. Substitution
1. DELETION A nucleotide is left out
This shifts the reading of the DNA over one resulting in an incorrect protein
AAG CCC GGC AAAAA CCC GGC AAA ← shifts over
Result: AAC CCG GCA AA
Met Lys Leu Ala His
Nucleotide deletion
mRNA
Protein Met Lys Phe Gly Ala
1. DELETION CONT’D
2. INSERTION An extra nucleotide is added
This shifts the reading of the DNA over one resulting in an incorrect protein
AAG CCC GGC AAAAAG ACC CGG CAA A
2. INSERTION CONT’D
FRAME SHIFT: 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.
3. SUBSTITUTION 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 AAAAAG ACC GGC AAA
mRNA
Protein Met Lys Phe Gly Ala
Base substitution
Met Lys Phe Ser Ala
3. SUBSTITUTION CONT’D
SILENT MUTATION
Amino acid is not changedDNA RNA Amino AcidCTA = GAU = AspCTG = GAC = Asp
TRY IT : 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 UUCC. GCU ACU UCA AUU C
3. What was the result of each mutation?4. Which would be most harmful?
TRY IT : Page 263
Questions: 2, 6, 7 Page 274
Questions: 10 (a, b)
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