proteins

• proteins

  contain N,O,H,C and sometimes S
• simplest amino acid is called glycene
• cysteine contains sulfur- disulfide bonds
• 20 different R-groups. they can be positive, negative or polar
• a bond between two amino acids is called a peptide bond and is formed in condensation and broken in hydrolysis
• amino acids contain a carboxyl group and an amine group
• an amine group has nitrogen and hydrogen
• amino acids

  -amine group

  -carboxyl group

  -r group

  -central carbon with a hydrogen bonded to it
• amphipathic


  having both hydrophilic (polar) and hydrophobic (non-polar) parts
• proteins used as

  enzymes, transport, storage, protection, building materials, structural
• polypeptides


  -long chain of amino acids joined together by peptide bonds- ribosomes.

  -often hundreds of amino acids joined together
• primary structure 


  -sequence of amino acids joined together in a polypeptide chain

  -determined by order of DNA in a gene. 20 amino acids- almost limitless
• secondary structure


  -coiling or folding of local regions of a polypeptide chain due to the formation of hydrogen bonds between backbone atoms.
• backbone atoms


  -anything not an r group

  -anything not a backbone atom is an r group
• 2 types of 3d shapes in polypeptides

  -alpha helix

  -beta sheet

  -both held together by hydrogen bonds
• alpha helix


  -H on the -NH group is attracted to the O on the -COOH group

  -H is electropositive and O is electronegative

  -H-bonds support helix

  -polypeptide coils up- helical

  -increase in temperature unravels helix- denaturation
• beta sheet


  -H-bonds hold adjacent peptide chains together
• tertiary structure


  -overall 3d shape of protein molecule- interactions between R-groups of amino acids

  -4 types of bonding involved:

  • hydrogen bonds
  • ionic
  • disulphide (cysteine)
  • hydrophilic and hydrophobic interactions (polar and non-polar bonds)
• quaternary


  -the way 2 polypeptide subunits are arranged to give a final specific shape

  -examples: collagen, haemoglobin

  -this doesn't apply to all proteins- some only have 1 polypeptide chain
• globular proteins


  -round and compact

  -rounded because of the tendency for hydrophobic R-groups to be on the inside of the molecule and hydrophilic R-groups on the outside

  -water- soluble- hydrophilic parts on the outside- soluble in blood plasma easily

  -haemoglobin, pepsin and insulin
• haemoglobin


  -binds to oxygen to form oxyhaemoglobin

  -dissociates to form haemoglobin

  -haem groups

  -alpha helix

  -quaternary- 2 subunits alpha 2 subunits beta

  -soluble
• haem groups


  -each subunit has a haem group

  -1 molecule of haemoglobin can carry 8 oxygen atoms or 4 oxygen molecules

  -prosthetic groups- permanent parts of a protein not made of amino acids

  -proteins containing prosthetic groups are called conjugated proteins

  -contains inorganic iron ion (Fe2+)
• secondary structures of haemoglobin


  -alpha helix
• tertiary structure of haemoglobin


  -alpha and beta chains fold and coil

  -disulfide bonds, ionic, hydrophilic and hydrophobic interactions, hydrogen bonds

  -hydrogen bonds hold the helix in place
• quaternary structure of haemoglobin


  -4 subunits

  -2 alpha and 2 beta

  -1 haem group per subunit

  -prosthetic group
• fibrous proteins

  -tough and rope shaped

  -insoluble- aids in its structural roles

  -unreactive, mechanically strong

  -regular, repeated sequences of amino acids in primary structure

  -hydrophobic on outside

  -strength- h-bonds, ionic etc

  -collagen, elastin, keratin
• collagen


  -strong, flexible and inelastic-strong, flexible and inelastic

  -connective tissues- skin, bones, teeth, tendons

  -3 polypeptide chains wrap around each other to form a triple helix

  -structure held in place by h-bonds
• collagen formation


  -3 polypeptide chains wrap around one another to form a triple helix

  -1 collagen molecule (3 polypeptide chains) form cross links to adjacent collagen molecules to form fibrils

  -many fibrils form collagen fibres

  -fibres can be arranged differently for different connective tissues
• pepsin


  -globular

  -digestive enzyme found in stomach

  -breaks down peptide bonds

  -tertiary structure- active site of enzyme

  -has no quaternary structure- 1 polypeptide chain

  -has some acidic R-groups- ability to tolerate stomach's low pH
• insulin


  -globular

  -blood glucose regulation

  -hormone

  -2 polypeptide chains that form disulfide bonds- quaternary structure

  -6 insulin molecules (12 polypeptide chains) form the overall globular structure

  -water soluble- hydrophilic on outside- blood plasma
• keratin


  -fibrous

  -hair, fur, claws, hooves, scales

  -flexible (hair) or hard/ rigid (claws)

  -insoluble- waterproof- prevent pathogens entering body (hydrophobic r-groups on outside)

  -disulfide bonds- strength
• elastin


  -fibrous

  -elastic- stretches and recoils- bladder, skin

  fibres- cross-links between chains and coils- provide its strength and elasticity
• quartenary structure 


  -proteins consisting of more than one polypeptide chain

  -proteins containing prosthetic groups