22.10 Genetic Mutations

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Chapter 22 Nucleic Acids and Protein Synthesis

• 22.10 Genetic Mutations
• 22.11 Recombinant DNA
• 22.12 Viruses

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Mutations

• A mutation
• Alters the nucleotide sequence in DNA.
• Can result from mutagens such as radiation and
  chemicals.
• Can produce one or more incorrect codons in the
  corresponding mRNA.
• Can produce a protein that incorporates one or
  more incorrect amino acids.
• Causes genetic diseases that produce defective
  proteins and enzymes.

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Normal DNA Sequence

• The normal DNA sequence produces a mRNA that
  provides instructions for the correct series of
  amino acids in a protein.

Correct order
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Mutation Substitution

• The substitution of a base in DNA changes a codon
  in the mRNA.
• A different codon leads to the placement of an
  incorrect amino acid in the polypeptide.

Incorrect order
Wrong amino acid
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Frame Shift Mutation

• In a frame shift mutation, an extra base adds to
  or is deleted from the normal DNA sequence.
• All the codons in mRNA and amino acids are
  incorrect from the base change.

Incorrect amino acids
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Genetic Diseases
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Recombinant DNA

• Recombinant DNA combines a DNA fragment from one
  organism with DNA in another.
• Restriction enzymes are used to cleave a gene
  from a foreign DNA and open DNA plasmids in E.
  coli.
• When the DNA fragments are mixed with the
  plasmids in E. coli, the ends are joined by
  ligase.
• The new gene in the altered DNA produces protein.

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Recombinant DNA

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Products of Recombinant DNA
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DNA Fingerprinting

• In DNA fingerprinting (Southern transfer)
• Restriction enzymes cut a DNA sample into smaller
  fragments (RFLPs).
• The fragments are sorted by size.
• A radioactive isotope that adheres to certain
  base sequences in the fragments produces a
  pattern on x-ray film, which is the
  fingerprint.
• The fingerprint is unique to each individual
  DNA.

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Polymerase Chain Reaction

• A polymerase chain reaction (PCR)
• Produces multiple copies of a DNA in a short
  time.
• Separates the sample DNA strands by heating.
• Mixes the separated strands with enzymes and
  nucleotides to form complementary strands.
• Is repeated many times to produce a large sample
  of the DNA.

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Polymerase Chain Reaction
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Viruses

• Viruses
• Are small particles of DNA or RNA that require a
  host cell to replicate.
• Cause a viral infection when the DNA or RNA
  enters a host cell.
• Are synthesized in the host cell from the viral
  RNA produced by viral DNA.

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Viruses
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Reverse Transcription

• In reverse transcription
• A retrovirus, which contains viral RNA, but no
  viral DNA, enters a cell.
• The viral RNA uses reverse transcriptase to
  produce a viral DNA strand.
• The viral DNA strand forms a complementary DNA
  strand.
• The new DNA uses the nucleotides, and enzymes in
  the host cell to synthesize new virus particles.

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Reverse Transcription
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HIV Virus and AIDS

• The HIV-1 virus is a retrovirus that infects T4
  lymphocyte cells.
• As the T4 level decreases, the immune system
  fails to destroy harmful organisms.
• Pneumonia and skin cancer are associated with
  AIDS.

HIV virus
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AIDS Treatment

• One type of AIDS treatment prevents reverse
  transcription of the viral DNA.
• When altered nucleosides such as AZT and ddI are
  incorporated into viral DNA, the virus is unable
  to replicate.

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AIDS Treatment

• Azidothymine (AZT) Dideoxyinosine
  (ddI)

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AIDS Treatment

• Another type of AIDS treatment involves protease
  inhibitors such as saquinavir, indinavir, and
  ritonavir.
• Protease inhibitors modify the active site of the
  protease enzyme, which prevents the synthesis of
  viral proteins.
• Inhibited by Inhibited by
• AZT, ddI protease inhibitors
• reverse
• transcriptase protease
• Viral RNA Viral DNA Viral
  proteins