Mutations
Changes to DNA
Regents Biology
2009-2010
Mutations





permanent change in a cell’s DNA
sequence
Includes changes in nucleotide
sequence, alteration of gene position,
gene loss, duplication, or insertion of
foreign sequences
Can be inherited if mutation is in gamete
Most mutations have a negative effect
Positive mutation? evolution
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Mutagen


Any agent that causes changes in DNA
Includes physical agents that damage
DNA
X-rays
 UV rays
 Cigarette tar
 Gamma rays
 carcinogens

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Mutant

An organism carrying a gene that has
mutated
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Mutations

Changes to DNA are called mutations
change the DNA
 changes the mRNA
 may change protein
 may change trait

DNA
mRNA
protein
trait
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TACGCACATTTACGTACG
AUGCGUGUAAAUGCAUG
aa aa aa aa aa aa aa
Classes of Mutations
1.
Gene level

2.
Mutations include different point &
frame-shift mutations
Chromosome level

Rearrangement of genes within or
between chromosomes
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Gene Level Mutations

Changes to the letters (A,C,T,G bases) in
the DNA

point mutation



change to ONE letter (base) in the DNA
may cause change to protein, may not
frameshift mutation



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addition of a new letter (base) in the DNA
sequence
deletion of a letter (base) in the DNA
both of these shift the DNA so it changes how
the codons are read
big changes to protein!
Point Mutations

One base change

can change the meaning of the whole protein
THEFATCATANDTHEREDRATRAN
THEFATCARANDTHEREDRATRAN
OR
THEFATCATENDTHEREDRATRAN
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Does this change
the sentence?
A LITTLE!
Point Mutations

Missense mutation = changes amino acid
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGUAUGCGAGUGA
MetArgValTyrValCysGluStop
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Does
this change
the protein?
DEPENDS…
Sickle cell anemia

Hemoglobin protein in red blood cells
strikes 1 out of 400 African Americans
 limits activity, painful & may die young

Normal
round cells
Misshapen
sickle cells
Only 1 out of
146 amino acids
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Point Mutations

Silent mutation = no change to protein
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGCUUGCGAGUGA
MetArgValTyrAlaCysGluStop
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Does
The this
codechange
has
repeats
the protein?
in it!
Why not?
Point Mutations

Nonsense mutation = change to STOP
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
Really destroyed
that protein!
AUGCGUGUAUAAGCAUGCGAGUGA
MetArgValStop
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Frameshift Mutations

Add or delete one or more bases

changes the meaning of the whole protein
THEFATCATANDTHEREDRATRAN
Does this change
the sentence?
A LOT!
Delete
Add one!
one!
THEFATCANTANDTHEREDRATRAN
OR
THEFATCAANDTHEREDRATRAN
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Frameshift Mutations

Addition = add one or more bases
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGUCAUGCGAGUGA
MetArgValTyrValMetArgValA
Regents Biology
Does this change
the protein?
A LOT!
Frameshift Mutations

Deletion = lose one or more bases
AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
AUGCGUGUAUACGAUGCGAGUGA
MetArgValTyrAspAlaSerGA
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Does this change
the protein?
A LOT!
Cystic fibrosis

Broken salt channel in cells

strikes 1 in 2500 white births

gene codes for a protein channel
that allows salt to flow across cell membrane


broken protein doesn’t work as channel
doesn’t allow salt out of cell, so water doesn’t flow out
either

thicker & stickier mucus coating around cells

mucus build-ups in lungs & causes bacterial infections

destroys lung function
without treatment children die before 5;
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with treatment can live past their late 20s

Salt channel
Effect on Lungs
normal lungs
airway
salt channel
salt
normal mucus
H 2O
cells lining
lungs
cystic fibrosis
salt
H 2O
transports salt through protein
channel out of cell
Osmosis problems!

thick mucus
mucus & bacteria build up
= lung infections & damage
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Deletion leads to Cystic fibrosis
deletion
Loss of one
amino acid!
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Chromosome Level Mutations

Mutation involving a large segment of
DNA
1.
2.
3.
Translocation
Inversion
Deletions
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Chromosome Level Mutations
Translocation
1.
Relocation of groups of base pairs from
1 chromosomes to another (usually
occurs between homologous
chromosomes)

New proteins can result

Eg. Some types of leukemia

Transposable element – fragments of
DNA that continue to move from 1
chromosomes to another (can disrupt
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transcription

Chromosome Level Mutations
Translocation
Inversion
1.
2.



3.
A sequence of DNA is inverted
(reversed)
ABC → CBA
Can disrupt base pairing
Deletions
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Chromosome Level Mutations
Translocation
Inversion
Deletions
1.
2.
3.


Involve loss of chromosomal material
Eg. Cancer – results of mutation in
genetic sequence
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Not to ask questions
is a mutation!
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