Protein Synthesis

• Protein Synthesis

  A) Transcription

  B) Translation

  C) Transcription

  D) mRNA

  E) DNA

  F) Ribosome

  G) Protein

  H) Replication

  I) RNA

  J) Protein

  K) 1

  L) DNA

  M) RNA

  N) Protein

  
• Transcription Diagram

  A) mRNA

  B) receptor protein

  C) ER membrane

  D) enzyme

  E) signal sequence

  F) polypeptide

  G) endoplasmic reticulum

  H) width

  I) ER

  J) Ribosome

  K) endoplasmic reticulum

  
• Transcription Diagram

  A) DNA Helicase

  B) hydrogen

  C) nucleotide

  D) mRNA

  E) mRNA

  F) reference

  G) RNA

  H) polymerase

  I) mRNA

  J) mRNA

  K) Phosphodiester

  L) backbone bonds

  
• Protein Synthesis, 2 main steps:

  • Transcription: Transfer coded information from nucleus to cytoplasm)
  • Translation: Conversion of information into polypeptides on ribosomes
  • Both use RNA
• Transcription

  • RNA-polymerase attaches to DNA region at start codon (methionine, UAG)
  • Length, for 1 gene, unwinds, catalysed by DNA helicase
  • Strands separate, h bonds break
  • One (coding) strand act as mRNA template
  • Ribonucleotides line up to complementary bases on template, joined by phosphodiester bonds catalysed by RNA polymerase
  • mRNA detaches and leaves through nuclear pore into cytoplasm
  • Before leaving nucleus, 1 guanine is added to 5’ end called cap (promotes translation)
  • 100 adenines added to 3' end; poly-A tail (signal for mRNA export and protection from enzyme action)
• Introns

  • ”Interruptions”
  • Non-coding regions in eukaryotic cells 
  • Removed from mRNA by enzyme action, after cap and tail have been added but before it leaves nucleus
• Translation

  • mRNA attaches to ribosomes at binding site (groove)
  • Two tRNA molecules held in position on ribosome at once
  • Anticodons on tRNA molecules bind to complementary codons on mRNA
  • Held by temporary h-bonds
  • First codon on mRNA, start codon, is AUG (methionine)
  • Ribosomes move along mRNA
  • Read codons
  • Translate into AA sequence; 15/sec added to polypeptide chain
  • Energy from breaking bonds between tRNA and AA form peptide bonds between AAs
  • Translation stops when ribosome reaches stop codon
  • No complementary tRNA
  • Polypeptide breaks away and folds
• After Translation

  • Completed polypeptides pass to cisternae of RER
  • Budded into RER vesicles
  • Pass to Golgi; modified to form functional proteins, packaged into Golgi vesicles
  • Many ribosomes (polysome) may become attached to same mRNA moving along in sequence to produce multiple of same polypeptide chain