1. Because Stuff Happens
Mutations

2. A. Mutation Overview
Any change or random error in the nucleotide sequence (either DNA or mRNA) is called a mutation
Can occur in any cell in body
Gamete: cell that determines sex; sperm or egg cell
Mutation passed down to offspring
Somatic cell: all other cells
Mutation stays with cell; may be copied in cell replication

3. Skin cancer is not inherited because it occurs in somatic or body cells

5. Two types of mutations:
Point mutation: one base is mutated into another (one amino acid change)
Frameshift mutation: one base is added or deleted (all amino acids changed)
Affects may be neutral (no change in expression), positive, or negative (disease or death)

6. A mutation in the thumb joint changed it to an opposable thumb = positive mutation!

7. Introns & Exons
Entire DNA strand is 3 billion (3,000,000,000) base pairs
In eukaryotes, divided into two types:
Introns: no coding information (nonsense)
Exons: code for proteins

8. Why would eukaryotic DNA have so many nonsense base pairs or junk?
Protection – mutation here wouldn’t harm protein (neutral mutation)
mutation
INTRON
EXON

9. Before mRNA leaves nucleus - therefore before translation (making proteins from mRNA) - introns must get cut out by process called splicing
Done by specific enzymes called spliceosomes

10. Point Mutation Single nucleotide (base, PO4, sugar) changes
Original : The fat cat ate the wee rat.
Mutation: The fat hat ate the wee rat.
Many diseases are result of single point mutation in gene

12. Sickle cell anemia
Point mutation: aa glutamine mutated into valine
Result: red blood cell changed from round shape to sickle (crescent) shape
Gets stuck on walls of blood vessels & can cause clog

13. Cystic fibrosis Point mutation: aa glutamine becomes STOP codon
Result: should be 1480 aa in protein, now only 493
Mucosal cells produce excess mucus which blocks ducts (tubes linking organs) which causes infections

14. Frameshift Deletion of nucleotide (base)
Any mutation which causes shift of codon sequences or incorrect amino acid number
Caused by two scenarios:
Deletion of nucleotide (base)
Original: The fat cat ate the wee rat.
Mutation: The fat ata tet hew eer at.
Insertion of extra nucleotide(s) (base)
Mutation: The fat caa tat eth ewe era t.
Many diseases caused by frame-shift mutations

15. Frameshift

16. Mutation: additional CAG in protein Result: early cell death in brain
Huntington’s Disease
Mutation: additional CAG in protein
Result: early cell death in brain
Huntington’s Disease
Normal

17. Mutation: extra GGG codons inserted on X chromosome
Fragile X Syndrome
Mutation: extra GGG codons inserted on X chromosome
Result: mental retardation in males
normal

18. Muscular dystrophy
Mutation: extra CTG or CCTG in muscle protein
Result: deteriorating (weakening) muscles

19. Tay-Sachs Disease Mutation: insertion of TACT in exon 11
Result: enzyme that breaks down fat in central nervous system (brain & spinal cord) defective
Fat accumulates on brain & spinal cord, permanently damaging cells & killing child before age 5

21. Point vs. Frameshift

22. Classwork Mutations worksheet
Use mRNA codes to look up amino acids in proteins
Do the same thing for the mutated mRNAs.
a. Where is the mutation? Either circle it or explain (G is now C or G got deleted/inserted)
b. What is the result? Describe the change to the amino acid(s) .

23. Homework
Do p. 220 #3-5
Do p. 222 #1-3, 8, 10-12
Study for a quiz tomorrow just on central dogma (25 points)
Transcription – DNA to RNA
Translation – RNA to protein
Know the process of transcription and translation (how it happens, where it happens, what happens)