Protein Examples

• Haemoglobin

  • Globular protein
  • Water-soluble
  • Has 4 polypeptide chains:
  • Two α-chains; 141 AA residues
  • Two β-chains; 146 AA residues
  • Transports oxygen fro lungs to respiring cells
  • Each chain contained prosthetic (“haem”) group
  • Contained iron ions (Fe^2^+)
  • Makes it red
  • Some animals have blue-green blood as they have copper instead
  • Bind to one oxygen molecule (O_2) each, 4 molecules total
  • Transported in erythrocytes;
  • Biconcave structures
  • No organelles, just cytoplasm
  • As much room for haemoglobin as possible
• Collagen

  • Fibrous protein
  • Insoluble in water
  • Contains 3 polypeptide chains wound around each other
  • Every 3rd amino acid is glycine
  • Allows chains to lie close, form tight coil
  • Held together by H bonds
  • Triple left-handed helix structure
  • Quaternary but no tertiary structure
  • Triple helices run parallel to each other
  • Covalent bonds form between via lysine R groups
  • High tensile strength
  • Flexible but no stretch
  • Main component of:
  • Tendons (connect muscles to bone)
  • Artery walls
  • Skin
  • Teeth
  • Bone
  • Over 25 naturally occurring types in body
• Pepsin

  • Globular
  • Water soluble
  • Large polymers joined by peptide-bonds
  • Must be stored at low temperatures (-50°C to -20°C) to prevent self-digestion
  • Folds into symmetrical tertiary structure, held together by H-bonds and 2 disulphide bridges
  • 43 amino acids with acidic R-groups (to be stable in the stomach’s acidic environment)
  • Very few amino acids with basic R-groups (4); to accept H^+ ions (little effect on enzyme structure)
  • Single polypeptide chain of 327 amino acids
  • Digests proteins in stomach (proteolytic enzyme)
• Insulin

  • Binds to glycoprotein receptors on muscle/fat cells to increase glucose uptake
  • Regulates blood glucose/sugar levels
  • “Storage” hormone (made in the Pancreas)
  • Amino acids have hydrophilic R groups (water-soluble)
  • Two polypeptide chains fold into tertiary structure
  • Joined by disulphide bonds
  • A chain begins with section of alpha helix
  • B chain ends with section of beta-pleated sheet
• Keratin

  • Long structures
  • Filaments arranged in bundles or fibres
  • Bonding:
  • Rich in cysteine; many disulphide bridges between chains
  • H bonding
  • Makes molecule very strong
  • Found in all hard parts of the body:
  • Nails
  • Scales
  • Claws
  • Feathers
  • Hooves
  • Fur
  • Horns
  • Provides mechanical protection
  • Impermeable barrier to infection
  • Waterproof prevents entry of waterborne pollutants
  • Some also found to regulate cell growth and protein synthesis
• Elastin

  • Random polypeptide chain network
  • Found where living things need to stretch/adapt shape
  • Coiling and cross-linking make it strong and extensible
  • In body:
  • Skin can stretch around bones and muscles because of it
  • Allow our alveoli to inflate and deflate
  • Bladder expand to hold urine
  • Blood vessels stretch and recoil (also helps maintain blood wave pressure)