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Mutations in DNA
Mutations
• Mutations: changes in the DNA
nucleotide sequence
• Occurs when:
– Errors are made during DNA
replication (copying)
– Errors are made during transcription
– DNA is exposed to mutagens
• Source of variation in living things
How do mutations affect the cell?
• Fact 1: Sequence of DNA codes for the
sequence of amino acids
• Fact 2: Sequence of amino acids determines
the shape of the protein
• Fact 3: Shape of a protein determines the
proteins functions (capabilities).
• Question: What’s the problem with
mutations?
• Answer: Mutations can create
nonfunctioning or malfunctioning proteins
OBJ 15
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Is mutation a bad word?
• Sometimes, yes!
• Many times, no!
– Mutations create variation in populations
– Variations can give individuals a greater
chance for survival (blubber in a whale,
fighting off an infection because of a newly
shaped immune system protein)
– Some mutations are “silent” in that they do
not affect protein shape and/or function
If I have a mutation in a gene thats
important for survival, will I die?
• Depends on severity of mutation (how
badly it alters the protein)
• Remember– we have TWO copies of each
gene (one from mom, one from dad).
– If one “normal copy” of a gene compensates
for a “broken copy”, the mutation is called
recessive
– If one broken copy is enough to do damage,
called a dominant mutation
Sickle Cell Point Mutation
Sickle vs. normal RBC
Phenylketonuria (PKU)
• Caused by a recessive mutation in the
gene that codes for an enzyme (PAH) that
converts phenylalanine, an amino acid, to
tyrosine, another amino acid
• Build up of phenylalanine byproduct
causes mental retardation
• http://www.dnaftb.org/ygyh/pku/cause.htm
Albinism
• Caused by a recessive mutation in a gene
that codes for an enzyme that makes
melanin
• Melanin gives hair, skin, and eyes
pigmentation, so a lack causes paleness
– Problems: sunburn, skin cancer, retina
damage
Tay-Sachs
• Recessive mutation in a gene that codes for a
protein that prevents lipid build up in brain cells.
– Lipid build up destroys brain cells
• Death occurs in early childhood
• More common in Ashkenazi Jewish populations
Cystic Fibrosis (CF) and
Huntington Disease (HD)
• CF: Recessive mutation that causes
damage to the lungs and pancreas
• HD: Dominant mutation that causes
progressive breakdown of brain cells.
– Occurs in middle age.