Ch. 12.4 Mutations

1
Ch. 12.4 Mutations

• Section Objectives
• Categorize the different kinds of mutations that
  can occur in DNA.
• Compare the effects of different kinds of
  mutations on cells and organisms.

2
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.
• the mutation results in a protein that is
  nonfunctional, and 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 body cell, it is not
  passed on to organisms 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.

4
Mutations

• Changes to DNA are called mutations
• change the DNA
• changes the mRNA
• may change protein
• may change trait

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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
• frameshift mutation
• 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!

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Point Mutations

• One base change
• can change the meaning of the whole protein

THEFATCATANDTHEREDRATRAN
Does this changethe sentence? A LITTLE!
THEFATCARANDTHEREDRATRAN
OR
THEFATCATENDTHEREDRATRAN
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Point Mutations

• Missense mutation changes amino acid

AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
Doesthis changethe protein? DEPENDS
AUGCGUGUAUACGUAUGCGAGUGA
MetArgValTyrValCysGluStop
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Sickle cell anemia

• Hemoglobin protein in red blood cells
• strikes 1 out of 400 African Americans
• limits activity, painful may die young

Normalround cells
Misshapensickle cells
Only 1 out of146 amino acids
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Point Mutations

• Silent mutation no change to protein

AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
Does this changethe protein? Why not?
The code hasrepeats in it!
AUGCGUGUAUACGCUUGCGAGUGA
MetArgValTyrAlaCysGluStop
10
Point Mutations

• Nonsense mutation change to STOP

AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
Really destroyedthat 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 changethe sentence? A LOT!
Add one!
Delete one!
THEFATCANTANDTHEREDRATRAN
OR
THEFATCAANDTHEREDRATRAN
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Frameshift Mutations

• Addition add one or more bases

AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
Does this changethe protein? A LOT!
AUGCGUGUAUACGUCAUGCGAGUGA
MetArgValTyrValMetArgValA
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Frameshift Mutations

• Deletion lose one or more bases

AUGCGUGUAUACGCAUGCGAGUGA
MetArgValTyrAlaCysGluStop
Does this changethe protein? A LOT!
AUGCGUGUAUACGAUGCGAGUGA
MetArgValTyrAspAlaSerGA
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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