Protein Synthesis

• Protein Synthesis

  • Production of protein from amino acids molecules using DNA for instructions
  • There are 20 different  amino acids, but unlimited combinations of these and unlimited types of proteins made.
• Functions of proteins

  • Tissue structure - e.g. keratin, collagen
  • Transport across cell membranes - e.g. channels, carriers
  • Communication - e.g. hormones, receptor proteins
  • Cell metabolism - e.g. enzymes
  • Cell recognition - e.g. glycoproteins
  • Cell movement - intra and extracellular
• Stage ONE - transcription

  • Creation of the mRNA template from DNA in the nucleus
• RNA

  • As DNA is too large to leave nucleus, a template of RNA (ribonucleic acid) is produced - called messenger RNA (mRNA)
  • RNA is a single strand of ribose sugars with the same bases as DNA, except uracil replaces thymine.
• stage 1

  1. At the start of the desired gene RNA Helicase makes double helix separate into 2 strands
  2. RNA polymerase attaches RNA nucleotides to exposed complementary bases on on DNA strand.

  • This continues until RNA polymerase reaches the end of the gene then it stops
  • Template strand = template that mRNA attaches to.
  • Coding strand = the strand with identical bases to mRNA (except U replaces T)

  1. Not all bases code for amino acids. Bases that don not (introns) are removed, leaving those that do (exons)
  2. The reaming mRNA leaves the nucleus to be translated at ribosome
• Stage TWO - translation

  • Production of proteins from mRNA template
  • Occurs on ribosomes.
  • Ribosome “reads three bases at a time (codon) and joins the associated amino acid to the protein.
• stage 2

  1. Ribosome attaches to end of mRNA. When it  reaches start codon (AUG) protein translation begins.
  2. Transfer RNA (tRNA) bring over amino acids to be joined

  • Each tRNA has a specific anti-condo (complimentary set of bases) at one end and an amino acid attached to the other end
  • The anti-codon attaches to the corresponding codon on the mRNA
  •   you can figure out which amino acid will be added to a protein by reading the codon on the mRNA then looking at a conversion table ——->
  • E.g. the codon AGU codes for the amino acid serine (Ser)
• stage 2

  1. A peptide bond forms between the new amino acid and the one before it using ATP

  • This is called elongation

  1. The amino acid detaches from the tRNA and tRNA disappears into the cytoplasm to collect a new amino acid and repeat the process
  2. When stop codon is reached, protein is finished and leaves the ribosome to be packaged in Golgi body
• Packaging Proteins for Secretion

  • Proteins leave ribosome, moving through endoplasmic reticulum to the golgi body
  • Proteins are modified by adding sugars, sulphates etc. and are enveloped in a vesicle.
• Protein Structure

  • Primary - single chain of amino acids
  • Tertiary - sheets and spirals are bent and folded
  • Secondary - single chain forms sheets or spirals
  • Quaternary - 2 or more chains join bent and folded