Transcription

1
Transcription Translation

• Chapter 17 (in brief)
• Biology Campbell Reece

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RNA vs. DNA

• DNA
• Four bases are adenine, guanine, cytosine
  thymine
• Sugar is deoxyribose
• Is a double-stranded helix

• RNA
• Four bases are adenine, guanine, cytosine
  uracil
• Sugar is ribose
• Is a single-stranded helix

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3 Types of RNA

• Messenger RNA (mRNA) carries the instructions
  for making the protein from the nucleus to the
  ribosomes
• Ribosomal RNA (rRNA) makes up a ribosome
• Transfer RNA (tRNA) carries the amino acids to
  the ribosomes

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Transcription

• The process of making RNA from DNA
• The DNA serves as a template for making the RNA
• Similar base-pairing rules apply
• Cytosine still pairs with Guanine
• But Adenine now pairs with Uracil

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Transcription The Process

• RNA polymerase pries the two strands of DNA apart
  and hooks together the RNA nucleotides
• Moves 3?5 along the DNA template strand
• Promoter the DNA sequence where the RNA
  polymerase attaches to begin transcription
• Terminator the sequence that signals the end of
  transcription

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Transcription The Process
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3 steps to Transcription

• Initiation the RNA polymerase binds to the
  promoter, DNA unwinds, RNA synthesis begins
• Elongation the polymerase moves along the DNA,
  elongating the RNA
• Termination the polymerase reaches the
  terminator, transcription stops, the RNA is
  released, polymerase detaches

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Introns and Exons

• Introns are noncoding regions of DNA or RNA
• Introns are in the way or are intervening and
  must be removed (RNA splicing)
• Exons are the coded regions that are expressed

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Translation

• The process of making the protein from the
  instructions on the mRNA
• Occurs in the ribosomes
• Codon a sequence of 3 bases that codes for a
  specific amino acid
• Anticodon the complementary 3 base sequence on
  a tRNA molecule

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Codons Anticodons
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Transcription The Process

• Initiation the mRNA attaches to the ribosome,
  the tRNA brings the first amino acid
• Elongation
• 1) codon recognition
• 2) peptide bond formation
• 3) translocation

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Elongation
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Transcription The Process

• Termination when a stop codon is reached, the
  polypeptide detaches, the mRNA leaves
• Stop codons UGA, UUA, UAG

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Substitution

• An incorrect base is substituted for a correct
  one
• Can result in no effect, missense or nonsense

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Insertion or Deletion

• An extra nucleotide is added or one is missing
• Results in frameshifts that can cause missense,
  nonsense, an extra amino acid, or a missing amino
  acid