Transcript GENE MUTATIONS - mrbemrose / FrontPage

GENE MUTATIONS
Introduction
Every normal cell carries a full
complement of genetic material
 A mutation can occur in:

a
somatic (body) cell
 a germinal (reproductive) cell – can be
transmitted to offspring
Introduction
Split this into codons!
Thesunwashotbuttheoldmandidnotgethishat.
 It should look like this...
The sun was hot but the old man did not get
his hat.
 What if we added another T at the beginning?
T hes unw ash otb utt heo ldm and idn otg eth
ish at.

Mutations...not all are bad!

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mutations are random changes in genetic
material
rare events
most mutations that are detectable are
detrimental
some mutations provide variation, allowing for
adaptation to the environment (can be favorable)
some mutations cannot be detected
Types of Mutations
Silent mutation:
 does
not result in a change in the amino acid
sequence of the protein,
 due to the redundancy of the genetic code
 or a change in the code on the introns.
Eg: The A.A. Phe is coded for by UUU and UUC… if U gets swapped for C
on the mRNA strand the mutation will have no effect. Phe will still be
coded for!
Missense mutation:
a
mutation that results in the single
substitution of one amino acid in the protein.
 E g. sickle cell anemia.
 Only affects one base pair on the DNA or one
codon of mRNA.
 Can be called a base pair substitution in this
case.
Sickle Cell Anaemia
Sickle cell anemia
Image Credit: http://explore.ecb.org/
Blood smear (normal)
Image Credit: http://lifesci.rutgers.edu/~babiarz/
Nonsense mutation:
a
mutation that converts a codon for an amino
acid into a stop codon (usually lethal to the
cell).
 Also called a chain termination mutation.

AAC – Codes for Asn but if changed to UAA it is now a stop codon

UGA, UAA and UAG are the stop codons!
Frame shift mutation:
 occurs
when the reading frame is changed.
 Base pair deletion (one is missing) or base
pair insertion (one is added).
 Changes the remainder of the code.
Point Mutation:
The previous examples are point
mutations.
 They involve one base pair!
 http://www.youtube.com/watch?v=kp0esid
Dr-c&feature=related
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Chromosomal mutation:
 shape
change or missing piece of
chromosome;
 can result in inactivation of the entire gene
Translocation mutation:
 occurs
when groups of
base pairs are relocated
from one area of the
genome to another,
 usually between two
nonhomologous
chromosomes.
 Results in a fusion
protein (two unrelated
gene sequences being
transcribed together)
Inversion:
 chromosomal
segment
reverses its
orientation.
 Gene control is
affected.

AUG UUU UUG CCU

UCC UUG UUU GUA
Some examples!!!
DNA
mRNA
Polypeptide
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Mutations: Additions
Addition:
TAG CAT GAG
becomes
TTA GCA TGA G
Mutations: Additions
A frame shift mutation
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
© 2010 Paul Billiet ODWS
Addition mutation
GGTGCTCCTCACGCCA
↓
CCACGAGGAGUGCGGU
↓
Pro-Arg-Gly-Val-Arg
Mutations: Deletions
Deletion:
TAG CAT GAG
Becomes
TGC ATG AG
A
Mutations: Deletions
A frame shift mutation
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
© 2010 Paul Billiet ODWS
Deletion mutation
GGTC/CCTCACGCCA
↓
CCAGGGAGUGCGGU
↓
Pro-Gly-Ser-Ala-Val
Mutations: Substitutions
Substitution:
TAG CAT GAG
Becomes
TCG CAT GAG
Similar Pro with one different A.A
Mutations: Substitutions
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
Substitution mutation
GGTCACCTCACGCCA
↓
CCAGUGGAGUGCGGU
↓
Pro-Arg-Glu-Cys-Gly
Substitutions will only affect a single codon
Their effects may not be serious unless they affect an amino acid that is
essential for the structure and function of the finished protein molecule (e.g.
sickle cell anaemia)
The genetic code is degenerate
A mutation to have no effect on the phenotype
Changes in the third base of a codon often have
no effect.
© 2010 Paul Billiet ODWS
No change
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
© 2010 Paul Billiet ODWS
Substitution mutation
GGTCTTCTCACGCCA
↓
CCAGAAGAGUGCGGU
↓
Pro-Glu-Glu-Cys-Gly
Disaster
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
© 2010 Paul Billiet ODWS
Substitution mutation
GGTCTCCTCACTCCA
↓
CCAGAAGAGUGAGGU
↓
Pro-Glu-Glu-STOP
What Causes Mutations?

Spontaneous mutations
 occur
under normal conditions.
 May involve mispairing during replication

Induced mutation
by mutagenic agents – chemical
agent or radiation
 Examples: (X-rays, formaldehyde, toluene,
UV…)
 caused
Page 263...great summary chart
 Do Q 1-4, 6
 A great site for review!
 http://learn.genetics.utah.edu
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