proteins

• formation of proteins

  • most important reaction of amino acids is polymerisation - via condensation reactions
  • living organisms -> enzymes catalyse the polymerisation of amino acids to form peptides and proteins
• formation of proteins

  
• ala-gly


  COOH of alanine reacts with the NH2 of glycine

  
• gly-ala


  COOH of glycine reacts with the NH2 of alanine

  
• gly-ala-ser


  tripeptide - formed from 3 amino acids

  
• adding 1 amino acid at a time to the growing chain or linking 2 peptide chains together can be used to form polypeptides - formed from many amino acids
• many remarkable achievements in peptide synthesis have been reported including the synthesis of human insulin
• hydrolysis of proteins

  • boiling the protein with 6 moldm-3 HCl for 24 hours hydrolyses all the peptide linkages
  • produces a mixture of all the amino acids in the original protein

  
• amino acids on TLC

  as they aren't coloured, you need to spray the plate with a chemical e.g. ninhydrin - shows the spots up as purple
• enzymes


  the active site of an enzyme binds the substrate molecules of a biochemical reaction, and is critical to its specificity and catalytic activity
• primary structure

  • the order of the sequence of the amino acids in a protein chain is called the primary protein structure
  • different proteins contain a different sequence of amino acids and have different primary structures
  • if a single amino acid is incorrect, the whole protein can be useless

  
• primary structure - sickle cell anaemia

  • the importance of this sequence of amino acid units is illustrated by the 'molecular disease' known as sickle-cell anaemia
  • people suffering from this disorder have a proportion of sickle-shaped RBC's
  • these sickle-shaped RBC cells absorb oxygen less efficiently than normal disc shaped cells
  • the vital difference in function has been shown to be due to the displacement of only 1 of the 574 amino acid units in the protein, haemoglobin

  
• secondary structure 


  caused by hydrogen bond interactions between amino acids within the same chain causing the chain to have areas of 3d sections
• secondary structure - a helix and B pleated sheets


  hydrogen bonding between the lone pair on oxygen of C=O and the hydrogen of the N-H in the B-pleated sheets
• tertiary structure

  • the protein helix may be bent, twisted or folded into a particular shape
  • mostly due to interactions between R groups on the amino acids that make up the protein
  • possible interactions include: H-bonding, ionic bonding, dipole-dipole interactions, S-S bonding
  • if the cord is wound into a spiral, the tightness of the spiral represents the secondary structure
  • the resulting spiral could then be folded like a coiled telephone cord, to represent the tertiary structure
• tertiary structure

  • hydrophobic interactions occur between the non-polar side chains in tertiary structures
  • disulphide bonds occur between 2 cysteine amino acids in tertiary structures
  • H-bonding occurs in secondary and tertiary structures
  • ionic interactions occurs between 2 oppositely charged ions in tertiary structures

  
• disulphide bond formation (cysteine)

  • the disulphide bond is formed by oxidation of -SH groups on 2 cysteine amino acids

  
• hydrogen bond formation

  • this section of protein shows primary structure
  • here, the H-bonds from between the lone pair of electrons on the oxygen in the C=O and the d+ H in N-H