Transcription

1
Transcription Translation

• Chapter 17

2
What You Need to Know!

• How to explain the process of transcription
• The steps to translation

3
Transcription

• Three stages
• Initiation
• Elongation
• Termination

4
Initiation

• RNA polymerase recognizes and binds to the
  promoter region (TATA box and polymerase binding
  site)
• Transcription initiation complex constructs
  upstream of the actual gene
• DNA is unzipped by RNA polymerase
• RNA polymerase starts matching free RNA
  nucleotides to the template DNA strand

5
Initiation
6
Elongation

• mRNA (pre mRNA in eukaryotes) grows to full
  length
• DNA 3 ? 5
• mRNA 5 ? 3
• RNA peels away from DNA
• Multiple RNA polymerase can be at work at one
  time making multiple mRNAs

7
Elongation
8
Termination

• RNA molecule synthesis is stoped when terminator
  sequence (stop codon) is reached

9
Animation of Transcription
10
RNA Processing

• Eukaryotes only

11
Translation

• Translation is the RNA-directed synthesis of a
  polypeptide
• RNA include
• mRNA (messenger RNA)
• rRNA (ribosomal RNA)
• tRNA (transfer RNA)

12
Ribosome

• Facilitate the coupling of tRNA anticodons with
  mRNA codons
• One large subunit and one small subunit
• Made of protein and rRNA
• Produced in the nucleouls
• 3D catalytic macromolecule
• Stability through internal base-pairing

13
Transfer RNA

• tRNA molecules have a specific nucleotide triplet
  (anticodon) on one end and an AA on the opposite
  end
• tRNA bind to specific AA based on their anticodon
• Anticodons share the same code as the original
  DNA template
• 3D catalytic molecule
• 3D stability through internal base-pairing

14
Translating

• 2 ribosomal subunits will assemble at the start
  of the mRNA (at the untranslated region UTR)
• tRNA enter at the A site
• tRNA drop off their AA at the P site
• tRNA leave at the E site
• AAs form the growing polypeptide chain

15
Animation of Translation
16
Polyribosome

• Usually one mRNA is translated by groups of
  ribosomes called a polyribosome
• Polypeptides will spontaneously fold into
  secondary and tertiary structures