Download 12.4 Mutation - Ignacio School District

Textbook pages 345-349
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Cells make mistakes during replication
A mutation is a permanent change in a cell’s
DNA
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What is a mutagen?
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• Substances (chemicals and radiation) which cause
mutations by damaging DNA (changes chemical
structure of bases to cause mispairing or bonding
to wrong bases)

Missense – DNA code is altered, codes for wrong
amino acid
 Point mutations – chemical change in just one base
pair
 Substitution – point mutation one base pair
exchanged for another (codes for wrong amino acid)

Nonsense mutations – change codon for amino
acid to a stop codon (cause early termination of
translation leads to proteins unable to function
normally)

Frameshift mutations – change the “frame”
of the amino acid sequence
 Deletions – loss of nucleotides in DNA sequence
 Insertions – additions of nucleotides to DNA
sequence


Duplication – section of DNA is repeated
Expanding mutation – increase in number of
copies repeated (tandem repeats), repeats
increase generation to generation


Changes in 1 amino acid changes sequence
affecting folding and stability
Sickle-Cell Anemia – caused by a point
mutation
 GAA changed with GUA causes hemoglobin
structure to change
 Abnormal folding of mutated protein causes
sickle shape in red blood cells

Other protein folding diseases: Alzheimer’s
diseases, cystic fibrosis, diabetes, and cancer

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Point mutations occur spontaneously
During replication, wrong nucleotide added
Chemicals
 Have chemical structure similar to nucleotides so they
can be substituted causing bad replication
 Useful in treating HIV

Radiation
 X-rays and gamma rays – cause free radicals which
react violently with DNA
 Ultraviolet – causes adjacent thymine to bind
together, makes a kink, inhibiting replication

Body Cell Mutations
 Also known as somatic cell mutations
 Becomes part of genetic sequence passed to
daughter cells
 Does not cause problems for cell – neutral
mutations
 If mutation results in abnormal protein, cell death
might occur

Sex Cell Mutation
 Also known as germ-line cell mutations
 Mutation is passed to offspring and will be present
in every cell of offspring
 These mutations do not affect function of cell
 Might affect offspring drastically