Protein synthesis

• Transcription


  1. DNA->pre mRNA

  2. RNA polymerase binds to the promoter

  3. Antisense strand of DNA acts as a template
• Pre mRNA -> mRNA

  1. Post transcriptional modifications

  2. 5' cap - stability

  3. Poly A tail - stability

  4. Splicing - removes introns, found between exons
• Transcription - Initiation


  RNA polymerase recognizes the promoter and separates DNA
• Transcription - Elongation


  1. RNA nucleotides pair complementary to DNA

  2. 5'->3'
• Transcription - Termination


  1. RNA polymerase reaches a stop codon

  2. Release of pre mRNA or mRNA from DNA

  3. DNA strands reform double helix
• Translation - Amino acyl


  tRNA brings the amino acid in
• Translation - Peptidyl


  1. Holds tRNA with growing polypeptide chain

  2. Peptide bond between the amino acid in A and P

  3. Bonding releases tRNA into E site
• Translation - Exit


  After tRNA enters, it is released from the ribosome
• Translation - Initiation


  1. mRNA binds to the small ribosomal subunit

  2. tRNA enters the P site and second on A site

  3. Peptide bond forms between the 2 tRNA
• Translation - Elongation


  1. Ribosomes translocate along mRNA

  2. tRNA moves from A to P

  3. Polypeptide increases in length on the P site

  4. tRNA without amino acids leave on the E site
• Translation - Termination


  1. Stop codon enters the A site

  2. Polypeptide released from the P site

  3. Polypeptide, tRNA and ribosomes detach and separate
• Protein modifications


  • Phosphorlyation
  • Glycosylation
  • Folding
  • Removal of methionine or part of a polypeptide chain
  • Forming a conjugated protein
• Non-coding DNA


  • Introns
  • Telomeres
  • Genes for tRNA
  • VNTRs and STRs
  • Promoter, silencer and enhancer regions
• There are 20 amino acids
• There are 64 codons
• The genetic code is universal - used in all life
• The genetic code is degenerate - more than one codon codes for the same amino acid
• AUG (met) is the start codon
• Sickle cell anemia


  • Caused by a single nucleotide mutation
  • Base substitution of GAG to GTG
  • Glutamic acid in each beta chain is replaced by valine
  • Blocks capillaries and reduces blood flow
  • Provides protection against malaria
• Promoter


  • Non coding section of DNA
  • Binding site for RNA polymerase
  • Regulated by transcription factors
• tRNA activating enzyme


  1. Specific amino acid and ATP bind to the enzyme

  2. The amino acid is activated by the hydrolysis of ATP and the bonding of AMP

  3. P-Pi are released

  4. tRNA specific to the amino acid joins the active site of the enzyme

  5. The amino acid binds to the attachment site on the tRNA, AMP is released

  6. The activated tRNA with amino acid attached is released from the enzyme
• Modification of pre-proinsulin


  1. Formation of proinsulin - A peptide is removed with the rough ER

  2. Formation of insulin - Proinsulin is sent to the Golgi apparatus and packaged into a secretory vesicle, Protein chain is removed to form an alpha and beta chain, Alpha and beta chains join by disulfide bonds, Insulin is secreted into the bloodstream by exocytosis
• Proteosomes


  • Large protein complexes that break down unneeded proteins to amino acids through hydrolysis
  • Proteins are marked for degrading by the attachment of a ubiquitin