Alevel Biology - Biological Molecules

• Monomers are smaller units which can create larger molecules and the polymers are made from lots of monomers which are bonded together
• Examples of monomers


  • Glucose
  • Amino acids
  • Nucleotides
• Examples of polymers


  • Starch
  • Cellulose
  • Glycogen
  • Proteins
  • DNA
  • RNA
• Condensation reaction to create polymers


  1. Joining two molecules together

  2. Creating a chemical bond

  3. Removing water
• Hydrolysis reaction to break apart polymers


  1. Breaking a chemical bond between two molecules

  2. Involves the use of water
• Monosaccharides


  • Glucose
  • Fructose
  • Galactose
• Disaccharides


  • Sucrose
  • Maltose
  • Lactose
• Polysaccharides


  • Starch
  • Cellulose
  • Glycogen
• Alpha glucose


  Hydrogen atom on top, hydroxyl group on bottom of carbon 1
• Beta glucose


  Hydroxyl group on top, hydrogen atom on bottom of carbon 1
• Glycosidic bond


  Chemical bond that forms between two monosaccharides to create a disaccharide
• Maltose is made from glucose + glucose, lactose is made from glucose + galactose, sucrose is made from glucose + fructose
• Starch


  • Stored in plants to provide chemical energy
  • Made from alpha glucose
• Cellulose


  • Provides structural strength in plant cell walls
  • Made from beta glucose
• Glycogen


  • Stored in animals to provide chemical energy
  • Made from alpha glucose
• Starch and glycogen have 1-4 and 1-6 glycosidic bonds, cellulose has only 1-4 glycosidic bonds</b>
• Amylose is an unbranched starch polymer, amylopectin is a branched starch polymer
• Cellulose forms long straight chains that align in parallel and are held together by hydrogen bonds
• Glycogen has a higher proportion of 1-6 glycosidic bonds compared to starch, making it more branched
• Triglycerides


  Lipid made of glycerol and 3 fatty acid chains, can be saturated or unsaturated
• Triglycerides


  • Store a lot of energy due to high ratio of energy-storing carbon-hydrogen bonds
  • Can act as a metabolic water source when oxidized
  • Do not affect water potential or osmosis
• Phospholipids


  Lipid made of glycerol, 2 fatty acid chains, and a phosphate group
• Phospholipids


  • Hydrophilic head attracts water, hydrophobic tails repel water
  • Can form a bilayer in water
• Amino acid


  Monomer that makes up proteins, has a central carbon, hydrogen, amine group, carboxyl group, and variable R group
• Forming a dipeptide


  Condensation reaction to remove water and form a peptide bond between two amino acids
• Forming a polypeptide


  Multiple condensation reactions to form peptide bonds between multiple amino acids
• Enzyme


  A protein in the tertiary structure that catalyzes reactions by lowering the activation energy
• Enzymes


  • Each enzyme is specific and can only catalyze one particular reaction
  • The active site is complementary in shape to the substrate
• Induced fit model


  The enzyme's active site slightly changes shape to mold around the substrate
• The induced fit model explains how enzymes lower activation energy by putting strain on substrate bonds
• Active site


  Complementary in shape to a particular substrate
• The induced fit model is the accepted model currently, not the lock and key model
• Enzyme catalysis


  1. Substrate binding

  2. Enzyme active site slightly changes shape to mould around substrate

  3. Strain and tension on bonds

  4. Activation energy lowered
• Factors affecting rate of enzyme-controlled reaction


  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration
  • Inhibitors
• Temperature effect


  Lower temperature = less kinetic energy = fewer successful collisions = fewer enzyme-substrate complexes = lower rate

  Higher temperature = bonds break = loss of 3D shape = fewer enzyme-substrate complexes = lower rate
• pH effect


  Either side of optimum pH = rapid denaturing of enzyme due to disruption of charges in active site
• Substrate concentration effect


  Insufficient substrate = fewer collisions = lower rate

  Saturated enzyme active sites = rate remains constant even with more substrate
• Enzyme concentration effect


  Insufficient enzyme = active sites saturated = lower rate

  More enzyme = more active sites = higher rate

  Surplus enzyme with no more substrate = no further increase in rate
• Inhibitors


  Competitive inhibitor binds to active site, preventing enzyme-substrate complexes

  Non-competitive inhibitor binds to allosteric site, changing active site shape and preventing enzyme-substrate complexes
• Biochemical test for starch

  Add iodine, positive test is blue-black colour