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)