Transcript DNA mutations power point

DNA MUTATIONS
Mutations are any change in the genetic make up of an organism
and can occur naturally or can be increased by mutagens.
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information
Types
Diseases
Mutagens
TYPES OF MUTATIONS
Mutations can be spontaneous or
natural as a result of errors in DNA
replication or gamete production.
POINT
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area for more
information
Error rate is 1 in
1,000,000 replications.
BLOCK
CHROMOSOMAL ABBERATIONS
Point mutations
•Involves a change to one of the DNA bases that makes up a gene.
•Also known as a MISSENSE mutation.
•Consequence varies depending on type of change.
Change DNA
Change amino
acid sequence
Change protein
Three types of point mutation
Change
organism
substitution
insertion
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deletion
Base Substitution
•Involves one base in the DNA being substituted by another.
But…
•This mutation only affects one codon in the gene.
DNA
DNA
ATA
ATT
mRNA
UAU
UAA
Tyr
STOP
TA C T T C AAA C C G C G T
C is replaced by T in the DNA.
•Known as NONSENSE mutation
•Totally different protein made
•Effect on organism can be dramatic
Also
T A C T T C AAAT C G C G T
•End result is a different amino acid in protein.
•Generally minor effect on protein/organism.
DNA
AGA
AGG
mRNA
UCU
UCC
Ser
Ser
•Serine is still added
•Known as a SILENT mutation
Base Insertion/Deletion
•Involves one base either being inserted or removed from the DNA sequence.
•Both these mutations affect all codons after the insertion or deletion.
•The earlier the mutation occurs in the sequence the greater the effect.
DNA
TA C T T C AAA C C G C G T
Dramatic
effect on
protein made.
Known as
frame shift
mutations.
T A C T T C AAAA C C G C G
BASE INSERTION
INSERTION
Trp
Arg
TA C T T C AA C C G C G TA
Block mutations
•Involves large scale changes in DNA segments on chromosome.
•Only occur during meiosis, formation of gametes (sex cells).
•Can affect the functioning of many genes
•Severe effect on functioning and characteristics of organism.
Change amino
acid sequence
Change DNA
Change protein
Four types of block mutation
inversions
deletions
translocations
duplications
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Change
organism
Deletion
•Section of chromosome is lost, anywhere from three bases to large segments.
•The DNA breaks due to the effect of mutagens.
A
B
C
D
E
break
A
B
C
G
H
STEP 1
G
H
STEP 2
genes
D
A
A
F
D
E
B
C
F
segment
is lost E
D
E
F
G
DNA ligase rejoins chromosome
H
F
G
H
STEP 3
Translocation
•Section of chromosome breaks and is joined to another chromosome.
•Problem when gametes formed-some receive extra genes, some deficient.
1 2
3
4
5
STEP 1
A
B
C
D
E
F
G
H
break
A
B
C
D1 2
E3
F 4 G 5H
STEP 2
D
E
F
G
H
segment removed
DNA ligase joins segment
A
B
C
D
1 2
D
E3
E
F4 G 5 H
F
G
STEP 3
H
Duplication
•Segment of one chromosome is added to the homologous chromosome.
•Problem when gametes formed-some have double the genes, some have no genes.
A
B
C
D
E
F
G
H
A
B
C
D
E
F
G
H
HE
F
G
H
E
F
G
H
HE
F
G
H
E
F
G
H
STEP 1
break
A
B
C
DA
B
CE
DF
G
D
STEP 2
segment removed
A
B
C
DA
B
CE D F
D
G
STEP 3
Inversion
•Section of chromosome falls out and rotates through 180o.
•DNA ligase rejoins section but the genes are in reverse order.
•There is no loss of genetic information.
A
B
C
D
F
E
G
H
STEP 1
break
A
segment rotates 180o
B
C
D
A
B
C
STEP 2
D
F
E
G
H
G
H
E
F
G
H
segment rejoins
A
D
C
B
E
F
STEP 3
Chromosomal
abberations
•Loss or gain of entire chromosomes- called aneuploidy.
•Main cause is non-disjunction of chromosomes during meiosis.
•Gametes end up with extra chromosome(s) or fewer than 23 chromosomes.
2 x 23
Normal diploid
(2N) human cell
containing 2 sets of
chromosomes.
<23,
>23
Mainly occurs with
sex chromosomes.
23
23
Through meiosis haploid
(N) gametes are produced,
containing only one set of
chromosomes.
XO
XX
XXX
XY
XYY
Examples
Turner syndrome
Normal female
Metafemale
Normal male
Jacob syndrome
Mutagens
•Chemicals or radiation that increase the likelihood of a mutation occurring.
•Rate of mutation induced by mutagen is proportional to the dose of mutagen.
•Mutagens cause a decrease in the stability of the DNA molecule.
•Thus DNA more susceptible to error during replication or meiosis.
•Incorporate into genome
•Trigger cancers
Ionising
radiation
•Nuclear
•UV rays
•X rays
Alcohol &
dietary factors
•High fat, alcohol
•Trigger cancers
Viruses &
micro-organisms
Types
Environmental
poisons/irritants
•Benzene, asbestos
•Tobacco tar, formaldehyde
Diseases
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about how it is caused by a mutation.
Down
syndrome
Sickle cell
disease
Cystic
fibrosis
Sickle cell disease
•Haemoglobin is made up of 4 polypeptide chains (2 alpha & 2 beta chains).
•Gene for beta chain is found on chromosome 11 and consists of 438 bases.
•A mutation occurs in the gene coding for the beta chain.
•The mutation is a substitution where adenine replace thymine on the DNA
template strand.
•As a result the amino acid valine replaces glutamic acid.
•This change the properties of the haemoglobin and results in distorted red
blood cells.
haemoglobin
HBB gene on
chromosome 11
normal red blood cell
sickle cell
This single point mutation has a dramatic effect. Individuals have
many health problems, eg weakness, jaundice, anaemia, heart &
kidney defects, brain damage, skin lesions and inflamed spleen.
Cystic Fibrosis
•Inherited disorder and occurs when an individual has both copies of the
faulty gene.
•The gene (CFTR) is found on chromosome 7 and normally contains 1480
amino acids.
•A mutation occurs whereby the 508th triplet (AAA) is deleted resulting in a
mutated CFTR protein of 1479 amino acids.
CFTR gene on
chromosome 7
•The abnormal protein is unable to control chloride ion balance in cells.
•The build up of chloride ions in cells results in severe effects.
• Individuals have reduced life expectancy, high salt levels, blocked airways,
pancreatic deficiencies and males are infertile.
triplet deleted
•Cystic fibrosis is relatively common and occurs 1 in every 2500 individuals.
506th 507th 508th 509th 510th
506th 507th 508th 509th 510th
DNA
mRNA
amino
acids
TAA TAG AAA CCA CAA
AUU AUC UUU GGU GGU
ile
ile
phe gly
val
DNA
mRNA
amino
acids
AAACCA CAA
TAA TAG AAA
AUU AUC
ile
ile
GGU GGU
gly
val
Down Syndrome
•Arise from having 3 copies of
chromosome 21
•known as trisomy-21.
•Individuals have characteristic facial features, are relatively short,
slowed intellectual and physical development.
•Two main types of Down syndrome-97% non-familial, 3% familial.
Non-familial
24
Familial
23
One of the parents has only 45 chromosomes.
A translocation has occurred where one of
no.15 and one of no. 21 have joined together.
One of the sex cells contain 23 but one of the
23 is the 15/21 chromosome.
One of the parent’s sex cells contains
two no. 21 chromosomes, due to nondisjunction during meiosis.
15
Parent 1
Parent 2
Down child
3 no.21
21
15/21