BY5.1 Protein Synthesis

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Genetic Coce

  • DNA is the store for the genetic code
  • DNA is made up of chromosomes that are divided into genes
  • DNA carries information needed to make a particular protein
  • the genetic code determines what reactions occur in an organism
  • genes control the formation of enzymes and proteins

Nature of the genetic code:

  • genetic code determines the primary protein structure
  • DNA codes in triplets
  • DNA has 4 bases (A,T,G,C)
  • the sequence of bases in a DNA chain codes for the sequence of amino acids in a polypeptide chain
  • genes are the protion of DNA that codes for a whole polypeptide
  • each amino acid is coded for by a codon (3 bases)
  • all codons are universal
    • they're exactly the same for all living organisms
  • the code is non overlapping
    • each triplet is read separately


there are 3 types of RNA:

  • messenger RNA (mRNA)
    • formed in transcription
  • ribosomal RNA (rRNA)
  • transfer RNA (tRNA)
  • DNA doesn't leave the nucleus and acts as a template for mRNA
  • mRNA carriers the insturctions needed for protein synthesis from the nucelus to the cytoplasm
  • ribosomes provide a suitable surface for the attachment of mRNA and the assembly of proteins


  • mRNA is copied from a specific area of DNA (the cistron)
  • RNA polymerase links to the DNA and DNA unwinds and unzips the relevant region
  • only one strand acts as the template
  • free RNA nucleotides align themselves to their complementary base pairs…


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