Transcription

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Transcription
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Central Dogma
DNA RNA Protein
Transcription
Translation
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The Players

• mRNA messenger RNA, transports DNA code from
  nucleus to ribosome
• tRNA transfer RNA, transfers amino acids from
  cytoplasm to ribosome
• Codons sequence of 3 bases that code for one
  amino acid
• Start Codon Codon that signifies the beginning
  of a polypeptide

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Players, continued

• Stop Codon signifies the end of a polypeptide
• Amino acids Building blocks of polypeptide
• Ribosome Organelle that provides site for
  protein synthesis (translation)
• RNA polymerase Enzyme that makes RNA using DNA
  template.

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A Closer Look at a Gene
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Transcription Step 1 Initiation

• RNA polymerase attaches to a section of the
  promoter region of DNA, called the TATA box
• long sequence of repeating bases (usually A and T
  only 2 H-bonds to break)
• upstream of start codon

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Step 2 Elongation

• RNA polymerase works 5 to 3, starting from
  start codon (promoter not copied)
• Only copies 1 DNA strand, called the sense (or
  template) strand.
• Other strand called the anti-sense strand.
• Either strand of DNA can be sense strand.
• RNA base sequence created is identical to
  anti-sense strand, except U is present instead of
  T

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Step 3 Termination

• Stop codon is transcribed, RNA lets go
• Termination sequence tells RNA polymerase to let
  go.
• DNA zips back up

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RNA ? mRNA (in eukaryotes)

• Fig 8.13, p 262
• 5 cap is added (made of GTP)
• 3 polyA tail is added (lots of Adenines added)
• Give protection against catabolic enzymes in
  cytoplasm

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RNA ? mRNA continued

• Introns are excised by spliceosome enzyme RNA
  complex
• Fig 8.11, p. 260
• Alternative splicing patterns can produce more
  than 1 type of protein.
• Fig 8.12, p. 261

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Last, but not least

• No proofreading of mRNA
• BUT
• More than 1 codon codes for one amino acid
  (except Start)
• Many transcripts are made from the same gene and
  dont last long in the cytoplasm
• So, mistakes are limited