proteins

• proteins are a diverse group of large and complex polymer molecules, made up of amino acids
• they have a wide range of biological roles including:

  • structural: proteins are the main component of body tissues, such as muscle,ligaments and hair
  • catalytic: all enzymes are proteins, catalyzing many biological reactions
  • signalling: many hormones and receptors are proteins
  • immunological; all antibodies are proteins
• structure of amino acid

  • COOH group
  • amine group
  • R group
• 2 amino acids can join together to form a dipeptide linked by a peptide bond
• primary structure

  • the sequence of amino acid in a protein/ in the polypeptide chain
• secondary structure

  • H bonds from between nearby amino acids in the chain, making it coil into alpha helix or beta pleated sheets
• tertiary structure


  the coiled or folded chain is often coiled or folded further , or bonds form between different parts of the polypeptide chain

  • forms its final 3D structure
• quaternary structure

  • functional protein made up of multiple polypeptides
  • way in which they are assembled together
  • eg haemoglobin is made from 4 polypeptide chains bonded together
• different bonds hold different structural levels together:

  • primary = held together by peptide bonds
  • secondary = held together by hydrogen bonds
• tertiary bonds

  • hydrophobic interaction = these amino acids orient towards the centre of the polypeptide to avoid the water
  • disulphide bridge: the amino acid cysteine forms a bond with another cysteine through it R group
  • Hydrogen bonds: polar "R" groups on the amino acid form bonds with other polar R groups
  • hydrophilic interactions: outward close to the water
  • ionic bonds: + charged R groups bond together
• quaternary bonds

  • tends to be determined by the tertiary structure of the individual polypeptide
• what are the 3 fibrous proteins?

  • collagen
  • elastin
  • keratin
• fibrous proteins - regular repetitive amino acid sequence making a parallel polypeptide chain held together by cross links - rope like fibres

  • insoluble
  • strong
  • fairly unreactive
• collagen

  • artery walls - prevents high blood pressure blood bursting walls
  • tendons connect muscle to bone
  • bones - hardened with calcium phosphate
  • cartilage
• keratin

  • found in many external structures such as finger nails, hairs, feathers and horns
  • hard and tough, rich in cysteine = lots of disulphide bridges and H bonding between polypeptide chains makes molecules strong
• elastin

  • found in elastic connective tissues such as skin, large blood vessels
  • give flexibility to expand when needed, but also to return to their normal size
• globular proteins are round and compact

  • the hydrophilic R group tend to pushed onto the outside
  • makes it soluble , easily transported in fluids
• globular proteins

  • haemoglobin
  • insulin
  • amylase
• haemoglobin

  • globular protein that carries O2 around the body in red blood cells
  • known as a conjugated protein as its a protein with a non-protein group attached (prosthetic group)
• insulin

  • hormones secreted by the pancreas- regulates blood glucose level
  • solubility is important as it needs to be transported in blood tissue
  • 2 polypeptide chains, held together by disulfide bonds
• amylase

  • catalyses the breakdown of starch in the digestive system
  • most enzymes are globular proteins
• what breaks down peptide bonds

  • protease enzyme
• hydrogen bonds

  • form between H atoms with a slightly + charge and - negative charge
  • these form in hydroxyl, carboxyl and amino group
• ionic bonds

  • form between carboxyl and amino groups to form an ionic bond