Biomolecules

• starch is made up of: amylose and amylopectin
• shape and structure of amylose: helical, straight-chained
• bonds in amylose: a-1,4 glycosidic bonds
• In amylose: -OH of carbon 2 projects, can form intrachain interactions, becomes more compact and can store more glucose residues (good energy storage)
• structure of amylopectin: branched
• bonds in amylopectin: a-1,4 and a-1,6 glycosidic bonds
• property of amylopectin: extensive branching→ provides many ends accessible to hydrolytic enzymes, allow for quick release of glucose residues
• shape and structure of glycogen: helical, branched (has properties of both amylose and amylopectin)
• shape and structure of cellulose: multiple long straight chains wound together, unbranched
• main function of cellulose: main structural component of plant cell walls
• bonds in cellulose: b-1,4 glycosidic bonds
• orientation of b-glucose monomers in cellulose: each alternate monomer is rotated 180 degrees to bring -OH group of carbon 1 and carbon 4 together
• why cellulose is insoluble:

  • extensive interchain hydrogen bonding, no -OH groups available to form hydrogen bonds with water
• how is cellulose adapted to its function as a structural molecule

  • b-1,4 glycosidic bonds are stable and not easily hydrolysed
  • extensive interchain hydrogen bonding, hydroxyl groups project outwards to form microfibrils
  • many cellulose molecules wound tgt→ microfibrils→ macrofibrils→ cellulose fibres (high tensile strength)
• function of triglycerides: energy storage molecule
• why triglycerides insoluble: triglycerides mostly made of non-polar hydrocarbon tails→ will not affect water potential of cell, will not diffuse out of cell
• bonds in triglycerides: 3 ester bonds forming during condensation
• peptide bond: formed between carboxyl group of one amino acid and amino group of another amino acid during condensation
• primary structure: a single polypeptide chain held together by peptide bonds
• secondary structure: regular coiling/pleating of a single polypeptide chain held by hydrogen bonds (intramolecular)
• alpha helix:

  • regularly coiled structure
  • stabilised by hydrogen bonds between carboxyl and amino group (C=O and n-H) of every 4th peptide bond
• beta-pleated sheet:

  • hydrogen bonds between adjacent regions of a single polypeptide chain
• tertiary structure: further folding and bending of a single polypeptide chain, becomes a globular molecule with a specific 3d conformation
• types of interactions in tertiary structure: hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bonds (intramolecular)
• quaternary structure: association of more than 1 polypeptide chains
• types of interactions in quaternary structure: hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bonds (intermolecular)
• shape and structure of haemoglobin:

  • globular, made up of 4 polypeptides
  • each subunit has a haem group
  • subunits held by weak hydrogen bonds, ionic bonds and hydrophobic interactions
• function of haemoglobin:

  • transport of oxygen, exhibits cooperative binding
  • one molecule of oxygen binds to one subunit, conformation change induced in the remaining 3 subunits, increasing affinity of the remaining 3 subunits for binding to oxygen
• shape and structure of collagen

  • fibrous protein
  • primary structure has repeating tripeptide glycine-x-y
• main function of collagen: essential component of connective tissues

  other functions: precursor molecule to synthesise other steroids, bile salts
• what contributes to high tensile strength in collagen

  • ordered helical structure of the polypeptides
  • extensive intermolecular hydrogen bonding
  • covalent cross-linking between lysine residues of adjacent tropocollagen molecules
  • staggered arrangement of fibrils that minimise points of weaknesses
  • fibrils form bundles of fibres
• why starch insoluble:

  • hydroxyl groups projected into the interior, cannot form hydrogen bonds with water molecules
  • advantage: starch can be stored in large amounts without affecting water potential of cells, good energy storage molecule
• hydrocarbon tails of triglycerides contain high number of C-H bonds, can be oxidised to give a large amount of energy per unit mass, can store twice as much energy as starch -> compact energy store
• structure of cholesterol: 4 fused rings with a hydroxyl group
• function of cholesterol: amphipathic (-OH group is hydrophilic, carbon rings are hydrophobic), regulate membrane fluidity within the phospholipid bilayer
• why cellulose synthesised at the cell surface membrane and not inside cell

  • cellulose too large to cross the cell surface membrane
  • cellulose is required outside the cell to form cell wall
  • cellulose synthase complex is embedded on the cell surface membrane