Download Ch. 12.4 Gene Regulation and Mutation

Mutations
Any change in DNA sequence is called a mutation.
Can be caused by errors in replication, transcription, cell
division, or by external agents.
If mutation occurs in gametes (sex cells) it will be passed
on to offspring.
May produce a new trait or it may result in a protein
that does not work correctly.
If the mutation results in a protein that is nonfunctional,
the embryo may not survive.
In some rare cases a gene mutation may have positive
effects.
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Mutations
If mutation takes place in a somatic (body) cell, it is not
passed on to an organism’s offspring.
 Damage to a gene may impair the function of
the cell.
 When that cell divides, the new cells also will
have the same mutation.
 Some mutations of DNA in body cells affect
genes that control cell division.
 This can result in the cells growing and dividing
rapidly, producing cancer.
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Mutations

Changes to DNA are called mutations
 change the DNA
TACGCACATTTACGTACG
DNA
 changes the mRNA
 may change protein
AUGCGUGUAAAUGCAUGC
mRNA
 may change trait
protein
trait
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aa aa aa aa aa aa aa
Types of 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
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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
AUGCGUGUAUAAGCAUGCGAGUGA
MetArgValStop
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Really destroyed
that protein!
Types of mutations

Changes to the letters (A,C,T,G bases) in the DNA
 Frameshift mutation
 addition of a new letter (base) in the DNA
sequence
 deletion of a letter (base) in the DNA sequence
 both of these shift the DNA so it changes how
the codons are read
 big changes to protein!
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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!
Causes of Mutations

Sometimes a mistake in base pairing during DNA
replication.

Many mutations are caused by factors in the
environment.

Any agent that can cause a change in DNA is
called a mutagen.

Mutagens include radiation, chemicals, and even
high temperatures.
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