Protein Synthesis

• Amino Acids


  Are linked together to form proteins
• Amino Acids

  • All have the same general structure
  • Each type differs from the others by having a unique 'R' group
• 'R' group


  The variable part of the amino acid
• 20 different amino acids are commonly found in proteins
• Types of Amino Acid

  • Amino acids with different types of 'R' groups have different chemical properties
• Polypeptide chains

  1. Amino acids are linked together in long chains by the formation of peptide bonds

  2. Long chains of such amino acids are called polypeptide chains
• Protein functions

  Can be classified according to their functional role
• Protein structure

  The production of a functional protein requires that the polypeptide chain assumes a precise structure comprising several levels
• Levels of protein structure

  • Primary structure - the sequence of amino acids in a polypeptide chain
  • Secondary structure - the shape of the polypeptide chain
  • Tertiary structure - the overall conformation (shape) of the polypeptide caused by folding
  • Quaternary structure - in some proteins an additional level of organisation groups separate polypeptide chains together to form a functional protein
• Genetic code

  DNA codes for assembly of amino acids
• Components of the genetic code

  • Triplets on DNA
  • Codons on mRNA
  • Anticodons on tRNA
• Each triplet codes for one amino acid but more than one triplet may encode some amino acids (the code is said to be degenerate)
• Start and stop sequences for polypeptide chain formation

  • Start: AUG
  • Stop: UAA, UAG, UGA
• Two base codons would not give enough combinations with the 4-base alphabet to code for the 20 amino acids commonly found in proteins (it would provide for only 16 amino acids)
• Many of the codons for a single amino acid differ only in the last base