Prokaryotic Genetics

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Prokaryotic Genetics
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Mutations

• Change in genetic material
• Mutations may be neutral, beneficial, or harmful.
• Often silent (Degeneracy of the code)
• Types of Mutation
• Base substitution (point mutation)
• Change in one base
• Three types
• Missense changes the codon and codes for
  different amino acid
• Nonsense changes the codon and codes for a stop
  codon
• Silent changes the codon, but codes for same
  amino acid
• Usually occurs if there is a change in the 3rd
  base
• Frameshift mutation
• Insertion or deletion of a few nucleotides
  causing a shift
• Often involves a long stretch of altered amino
  acids leaving a non functional protein

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Example of Point Mutations
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Example of Frameshift Mutations
Figure 8.16a, d
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Problem

• Below is the original DNA and different
  mutations. Determine what amino acids would be
  produced from each and which contain missense,
  nonsense, silent and frameshift mutations.
• Normal template DNA 3 TACAACCTG 5
• Mutation 1 3 TACATCCTG 5
• Mutation 2 3TACAACCTA 5
• Mutation 3 3TACCACCTG5
• Mutation 4 3TACAACGCTC5

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Types of Mutagens

• Mutagens
• Agents that causes mutations.
• Spontaneous mutations
• Occur in the absence of a mutagen
• Chemical
• Nucleoside analogs
• Molecules similar to normal bases but cause
  altered base pairing
• Thymine binds with adenine but 5- bromouracil
  pairs with cytosine
• In the next generation AT base pairs will have
  become CG base pairs
• Radiation
• Ionizing radiation (X rays and gamma rays)
• Causes the formation of ions that can react with
  nucleotides and the deoxyribose-phosphate
  backbone
• Nonionizing radiation (UV light)
• Causes thymine dimers, which leads to problems
  with replication and transcription