12.4 Mutations

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12.4 Mutations
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Think About It!

• Complete the 2 tables on the first page of your
  handout. Try this without using your notes first
  and only refer to your notes on transcription and
  translation if you are struggling.
• From your tables and both translated sequences,
  what do you think a mutation is?

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What is a mutation? And what can a mutation do?

• A mutation is a permanent change in the DNA
  sequence of a gene.
• Mutations in a gene's DNA sequence can alter the
  amino acid sequence of the protein encoded by the
  gene.

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Mutations happen REGULARLY

• May occur in somatic cells (arent passed to
  offspring)
• Skin cancer and leukemia
• May occur in gametes (eggs sperm) and be
  passed to offspring
• Certain types of cancer the eye tumor
  retinoblastoma and Wilms tumor, a childhood
  malignancy of the kidney.

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• Most mutations have no effect on gene expression
• Many mutations are repaired by enzymes
• Some mutations may improve an organisms
  survival (beneficial) and/or produce genetic
  variety

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Mutations to control genes can transform one body
part into another. Scientists have studied flies
carrying Hox mutations that sprout legs on their
foreheads instead of antennae!
Polydactyly Common disorder with extra fingers
and/or toes
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How do mutations happen?

• The DNA sequence of each gene determines the
  amino acid sequence for the protein it encodes.
  We can think about the DNA sequence of a gene as
  a sentence made up entirely of three-letter
  words
• Thesunwashotbuttheoldmandidnotgethishat.
• The DNA sequence is interpreted in groups of
  three nucleotide bases, called codons.
• The sun was hot but the old man did not get his
  hat.
• Each codon or 3-letter word in this case,
  specifies a single amino acid in a protein.

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The sun was hot but the old man did not get his
hat.

• This sentence represents a gene.
• Each letter corresponds to a and each word
  represents a .
• What would happen if you shifted the three-letter
  "reading frame? You would end up with
• T hes unw ash otb utt heo ldm and idn otg eth
  ish at.
• Or
• Th esu nwa sho tbu tth eol dma ndi dno tge
  thi sha t.

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What other types of mutations can occur in DNA
sentences?

• Point mutations are single nucleotide base
  changes in a gene's DNA sequence. This type of
  mutation can change the gene's protein product in
  the following ways

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3 Types of Point Mutations

• Missense mutations result in a single amino acid
  change within the protein.
• Nonsense mutations create a premature
  "translation stop signal" (or "stop" codon),
  causing the protein to be shortened.
• Silent mutations do not cause amino acid changes
  within the protein.

• Exs
• Cystic Fibrosis
• Neurofibromatosis
• Sickle Cell Anemia
• Tay-Sachs
• Color Blindness

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Missense Mutation
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Nonsense Mutation
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Insertion mutations deletion mutations

• Add or remove one or more DNA bases.
• Insertion and deletion mutations cause frameshift
  mutations, which change the grouping of
  nucleotide bases into codons. This results in a
  shift of "reading frame" during protein
  translation.

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Insertion Mutation
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Deletion Mutation
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But mutations can also be beneficial

• Lactose Tolerance
• Antibiotic Resistance
• HIV Immunity
• Malarial Resistance from Sickle Cell Anemia

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Or they could be induced

• Mutagens
• Carcinogens
• Radiation
• UV light
• Environmental
• Heavy metals
• Chemical exposure (VOCs)
• Bacteria and Viruses

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Skin Cancer
Skin cancer occurs when errors (mutations) form
the in the DNA of healthy skin cells. The
mutations cause the cells to grow out of control
and form a mass of cancer cells
The World Health Organizations International
Agency for Research on Cancer (IARC) announced
that it has moved UV tanning beds to its highest
cancer risk category -- "carcinogenic to humans."
The use of tanning beds before age 30 is
associated with a 75 increase in melanoma risk.
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Lung Cancer
Smoking causes 87 of all lung cancer
cases. Smokers have approximately one chance in
10 of developing lung cancer over his/her
lifetime. 
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Videos

• Sickle Cell http//www.dnalc.org/resources/3d/17
  -sickle-cell.html
• Mutating virus http//video.nationalgeographic.c
  om/video/national-geographic-channel/shows/naked-s
  cience/ngc-deadly-mutation/
• Radiation leading to mutations and cancer
• http//www.dnai.org/lesson/go/1738/1419
• Addition and deletion mutations
  http//highered.mcgraw-hill.com/sites/0072556781/s
  tudent_view0/chapter11/animation_quiz_4.html