translation

• ribosomes read genetic code and make polypeptide
• ribosomes are composed of 82 proteins and 4 RNA
• ribosomes catalyse peptide bond formation
• ribosomes have 3 binding sites for tRNA, E P and A
• tRNA is an adaptor between amino acid and mRNA
• a specific amino acid binds to 3 end of tRNA
• codon in mRNA base pairs with anticodon in tRNA to bring correct amino acid to polypeptide
• mRNA

  template that specifies amino acid sequence, copied from dna
• tRNA

  adaptor that base pairs with mRNA to bring correct amino acid to the polypeptide
• rRNA

  catalyses peptide bonds that joins the amino acids
• start codon for translation

  AUG
• stop codon

  UGA, UAG, UAA
• A site

  binds a tRNA with amino acid as it first enters ribosome
• P site

  binds tRNA attached to growing polypeptide chain
• N terminus

  start of protein
• C terminus

  end of protein
• release factor causes disassembly of ribosomal subunits
• secreted proteins will have signal sequence in N terminus
• nuclear, mitochondrial, and cytoplasmic proteins complete translation on free cytoplasmic ribosomes
• ribosomes translating membrane bound and secreted proteins move to rER membrane to complete protein synthesis
• signal sequence binds to SRP to make translation pause
• anticodon loop binds mRNA
• incoming tRNA with amino acid inserts in A site to base pair with mRNA
• empty tRNA leaves via E site
• mature mRNA leaves nucleus to go to cytoplasmic ribosomes to start translation
• when a protein is imbedded in the membrane, it will have a stop transfer sequence, which traps protein in the lipid bilayer