Module 3: Central Dogma

• DNA: double stranded, thyamine base, flexible
• mRNA: translation of DNA
• tRNA: double stranded, turns nucleic acids to amino acids
• rRNA: double-stranded, catalyzes (2' OH) protein synthesis
• DNA double helix is formed by base pairs (A-T and G-C)
• DNA double helix stabilized by base stacking, VDW forces
• Transcription steps (DNA to RNA)

  1. Recognition
  2. Formation of open complex
  3. Elongation
  4. Termination
• recognition: sigma subunit in RNA polymerase recognized promoter (transcription start site)
• elongation: RNA polymerase makes new strand 5' to 3'
• in elongation RNA polymerase copies coding strand (mRNA) and tests base pairs on template strand
• termination: RNA polymerase recognizes terminator and releases complex
• rho-independent: hairpin loop destabilizes RNA polymerase
• rho-dependent: binds to open stretch of mRNA, disrupts RNA-DNA helix
• RNA: uracil base (demethylated cytosine), 2' OH
• recognition in archaea/eukarya

  • TATA binding protein recognizes TATA sequence
  • transcription factor B binds to BRE
  • changes DNA structure for RNA polymerase to recognize
• what happens if a promoter is deleted?

  gene won't be transcribed
• what happens if a terminator is deleted?

  normal function, will leave open stretch of mRNA for rho-dependent termination
• translation: nucleotide to amino acid
• translation requires code (base triplets) and translator (tRNA synthetase, charged with correct amino acid)
• Initiation:

  1. mRNA shine dalgarno sequence binds to rRNA
  2. tRNA enters p site
  3. 50 S subunit added, second tRNA enters A site
• Elongation:

  1. amino acids on 2 tRNA form peptide bond
  2. removed peptide from tRNA, advance empty tRNA to E site and peptide to P site
  3. new charged tRNA enters A site
  4. termination at stop codon
• in transcription DNA moves through the complex
• transcription and translation are coupled in prokaryotes