because stuff happens. a. mutation overview any change or random error in the nucleotide sequence...
TRANSCRIPT
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)