Proteins

• What are proteins 


  Proteins are polymers and their monomers are amino acids
• what determines function and shape of proteins

  sequence , type and number of amino acids
• what are some examples of proteins

  Enzymes

  cell me brain proteins

  hormones

  immunoproteins

  structural and carrier proteins
• amino acids fact sheet

  monomers of proteins

  20 different amino acids

  general structure is a

  carbon atom , a amine (NH2),carboxylis acid (COOH) , hydrogen atom and a R group which is a variable side chain
• which bond joins amino acids together

  Joined together by peptide bonds in condensation reaction and molecule of water released
• how is peptide bond formed

  hydroxyl group from one amino acid (OH) is lost from carboxyl group of one amino acid and joins with hydrogen from another amine group(NH2) in another amino acid in a condensation reaction and a molecule of water is lost
• what are dipeptides and poly peptides

  dipeptides are formed by condensation of two amino acids

  polypeptides formed by condensation of many amino acids
• how can chromatography be used to separate amino acids

  spots of non standard solutions of amino acids are placed on line and chromatography paper suspended in solvent

  each amino acid has different solubility so move different distance and times depending on charge and size

  unknown acids identified by comparing and matching with known spots from the amino acid sample mixture at same distance from line
• what is primary structure of protein

  sequence of amino acids bonded by covalent peptide bonds

  specific for each protein and affects shape and function of protein
• what is secondary structure of a protein

  weak negatively charged nitrogen and oxygen atoms interact to form hydrogen bonds. due to sequence in primary structure can form alpha helix or beta pleated sheets
• what breaks hydrogen bonds in secondary structure

  high temperature and ph change
• what is tertiary structure of a protein 


  Further conformational change of secondary structure leds to additional bonds forming between R chains

  bonds can be hydrogen , disulphide ionic and weak hydrophobic interactions between non polar R groups
• what is the quaternary structure of a protein 


  when proteins have more than one polypeptide chain working together as a functional macromolecule
• When do disulphide bonds form 


  form between two cysteine R groups as only amino acid with available sulphur atom in R group
• test for proteins 


  Add biurett solution and sample changes from blue to lilac/purple if protein present . The test is qualitative
• Globular proteins fact sheet 


  Compact and roughly spherical and soluble in water .

  can be easily transported around organisms and involved in metabolic reactions due to solubility

  have specific shapes so acts as enzymes

  functional and physiological function

  irregular and wide range of R groups

  examples enzymes , insulin haemoglobin
• how are globular proteins soluble

  non polar hydrophobic r groups face inwards of protein

  polar hydrophilic r groups face outwards

  soluble as water molecules can surround polar R group
• Fibrous proteins fact sheet 


  Long strands of polypeptide chains and have cross linkages due to hydrogen bonds

  little or no tertiary structure

  insoluble as large number of hydrophobic R groups

  omitted number of repetitive amino acid sequences

  used for structural role as repetitive sequence creates organised strong chains and insoluble

  examples keratin ,collagen
• structure of collagen 


  3 polypeptide chains held closely together by hydrogen bonds

  each polypeptide is a helix shape and contains 1000 amino acids

  in primary structure every third amino acid glycine on inside which allows chains to be arranged tightly forming triple helix

  covalent bonds form cross links between R groups of amino acids in interacting triple helices . this holds molecule together to form fibrils

  collagen molecules arranged in fibrils so that there are staggered ends

  many fibrils form collagen fibres

  fibres positioned so they are lined up with forces they withstand