MUTATIONSBecause Stuff Happens

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

Skin cancer is not inherited because it occurs in somatic or

body cells

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)

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

B. 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

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

INTRON INTRONEXON

mutation

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

C. 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

Sickle cell anemia Point mutation: aa glutamine mutated into valine

Result: red blood cell changed from round shape to sickle (crescent) shapeGets stuck on walls of blood vessels & can cause clog

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

D. Frameshift 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)Original: The fat cat ate the wee rat.Mutation: The fat caa tat eth ewe era t.

Many diseases caused by frame-shift mutations

Frameshift

Huntington’s DiseaseMutation: additional CAG in protein

Result: early cell death in brain

Huntington’s Disease

Normal

Fragile X SyndromeMutation: extra GGG codons inserted on X chromosome

Result: mental retardation in males

normal

Muscular dystrophyMutation: extra CTG or CCTG in muscle protein

Result: deteriorating (weakening) muscles

Tay-Sachs DiseaseMutation: insertion of TACT in exon 11

Result: enzyme that breaks down fat in central nervous system (brain & spinal cord) defectiveFat accumulates on brain & spinal cord, permanently damaging cells & killing child before age 5

Point vs. Frameshift

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) .

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)