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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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the sun was hot but the ol’ man did not get his hat
the sun was hot but the old man did not get his cat
the sun was hot but the old . an did not get his hat
the dsu nwa sho tbu tth eol dma ndi dno tge thi sha t
4
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.