Proteins

• • made from monomers called amino acids and when many join together they form polypeptides
  • structure of an amino acid = central carbon surrounded by amino group ( -NH2) , carboxylic acid group (-COOH) , hydrogen , and an r group ( this controls what amino acid is formed)
• • amino acids join together through condensation reactions between -OH and -H of two separate amino acids
  • the bond that joins the 2 amino acids is called a peptide bond and a dipeptide molecule is formed
  • peptide bonds can be broken by hydrolysis
• primary protein structure

  • sequence of amino acids in a polypeptide chain

  (changing the sequence of amino acids changes the protein/ polypeptide chain)
• secondary protein structure

  • when primary structure folds (b-plated sheet) coils (a-helix chain) due to hydrogen bonds formed between -NH and -C=O groups on amino acids in the polypeptide
• tertiary protein structure

  • formed when secondary structure folds/coils further due to interactions between R groups creating a 3D structure
  • Interactions include:

  - ionic bonds , disulphide bonds (very strong ) , hydrophobic reactions , hydrophillic reactions , hydrogen bonds (weak)

  
  

  the protein can function at this level
• quaternary protein structure

  • when more than one polypeptide chain joins together to make a protein. Also a 3D structure e.g haemoglobin
• TESTING FOR PROTEINS - BIURET TEST

  • place sample of solution (if solid must be crushed and dissolved in water) in a test tube and add an equal volume of sodium hydroxide solution and shake
  • add a few drops of dilute copper sulfate solution and mix gently
  • positive result = blue to purple