Transcript GENE MUTATIONS

MUTATIONS
Changes in DNA that affect
genetic information
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

Are Mutations Helpful or
Harmful?
Mutations happen regularly
 Almost all mutations are neutral
 Chemicals & UV radiation cause
mutations
 Many mutations are repaired by
enzymes

What Causes Mutations?

There are two ways in which DNA can
become mutated:
 Mutations

can be inherited.
Parent to child
 Mutations
can be acquired.
Environmental damage
 Mistakes when DNA is copied

Are Mutations Helpful or
Harmful?
 Some
type of skin cancers and
leukemia result from somatic
mutations
 Some mutations may improve an
organism’s survival (beneficial)
Immunity to HIV
Chromosome Mutations

May Involve:
Changing the
structure of a
chromosome
The loss or gain of
part of a
chromosome
Chromosome Mutations
 Five
types exist:
Deletion
Inversion
Translocation
Nondisjunction
Duplication
Gene Mutations
 Change
in the nucleotide
sequence of a gene
 May only involve a single
nucleotide
 May be due to copying errors,
chemicals, viruses, etc.
DNA (antisense strand)
mRNA
Polypeptide
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
The antisense strand is the DNA strand which acts as
the template for mRNA transcription
Types of Gene Mutations
 Include:
Point
Mutations
Substitutions
Insertions
Deletions
Frameshift
Point Mutation
 Change
of a single nucleotide
 Includes the deletion, insertion,
or substitution of ONE
nucleotide in a gene
Point Mutation
 Sickle
Cell
disease is the
result of one
nucleotide
substitution
 Occurs in the
hemoglobin gene
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)
© 2010 Paul Billiet ODWS
No change
Normal gene
GGTCTCCTCACGCCA
↓
CCAGAGGAGUGCGGU
Codons
↓
Pro-Glu-Glu-Cys-Gly
Amino acids
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
Frameshift Mutation
 Original:

The fat cat ate the wee rat.
 Frame
Shift (“a” added):
 The fat caa tat eth ewe
era t.
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
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
Gene Mutation
Animation
Background to Phenylketonuria
Phenylalanine and tyrosine
are two amino acids that
humans obtain from protein
in their diet. During normal
metabolism, excess
phenylalanine is acted upon
by an enzyme
(phenylalanine hydroxide).
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Phenylketonuria: aka - PKU
PKU is a hereditary
disorder caused by a
genetic defect which
disrupts this metabolic
pathway.
 An affected person lacks
the normal allele of the
gene required to make the
enzyme Phenylalanine
Hydroxide

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Phenylketonuria: Continued


Owing to this inborn error in
metabolism, phenylalanine is
no longer converted to
tyrosine.
Instead it undergoes
alternative pathways which
produces toxins which affect
the metabolism of brain cells
and severely limit mental
development.
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Screening for PKU –
Newborn babies are
screened for PKU, and
sufferers are put on a diet
containing minimum
phenylalanine.
 As a result the worst
effects of PKU can be kept
to a minimum.

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Albinism
Albinism results from a mutation
which prevents the formation of
enzyme 3 (Melanocyte Tyrosinase).
 As a result albinos fail to synthesize
melanin.

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Albinism – the symptoms


Due to the total lack of the pigment melanin Albino’s
have characteristic
 Very pale skin which fails to tan.
 White hair
 The colour of the iris is usually blue/gray or light
brown with some people having a reddish or violet
hue reflected through the iris.
 In some cases there is vision problems.
They must avoid ultraviolet radiation and may require to
ware tinted glasses to assist with photophobia.
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Albinism
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Cystic Fibrosis



Mucus is a slimy substance
secreted by the inner lining of
the wind pipe and intestine.
Mucus is made of a glycoprotein
which makes it thick, slimy and
perfect for protection and
lubrication.
The genetic information for
coding this glycoprotein is on
chromosome 7.
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Cystic fibrosis:
due to gene mutation

If the info on the gene for the glycoprotein
is altered.... Two outcomes.....
Homozygous for the mutant allele: Make
abnormally thick and sticky mucous leading
to lung congestion and blockage of the
pancreatic duct = CYSTIC FIBROSIS.
2. Heterozygous for the mutant allele: they carry
the mutant allele masked in their genotype
1.
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Cystic fibrosis
10/04/2016
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Mutagenic agents –
Increases mutation rate.

These include
A



variety of chemicals act as mutagens. E.g.
Bromouracil, are structurally similar to DNA bases, and are
inserted in place of normal bases.
Ethidium bromide has a structure that allows it to wedge
within the DNA double helix
Peroxides and mustard gas, chemically modify DNA.
 Exposure
to high-energy radiation (bombardment by
alpha, beta, or gamma particles) or ultraviolet light can
have a similar effect.
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Example of chemical mutations
Mrs Smith: Ch13: Mutations an
Chromosomal Abnormalities
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The Chernobyl Babies –
Radiation causes birth defects
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Some mutations even make it
on SNL!