Enzymes

• Key Enzyme Facts

  • Large globular protein
  • Complex 3D shapes
  • Primary to at least tertiary structure (possibly quaternary),
  • Biological catalysts (speed chemical reactions, not changed or used)
  • Product formation up to a million times faster
  • Catalyse one reaction (specificity)
  • Binding is at active site which has complementary shape to substrate
  • Forms enzyme-substrate complex (ESC)
  • Substrate form temporary H-bonds to R groups in active site
  • Active site small (rest enzyme maintains active site)
  • Products released; no longer complementary (also charges may have changed)
• Enzyme Reaction Types

  • Anabolic
  • 2 or more substrates combined to form product
  • Build up molecules
  • Catabolic
  • Substrate is broken to form 2 or more products
• Theories

  • Lock and Key
  • Substrate has complementary shape to enzyme’s active site
  • So substrate resembles ‘key’ that fits into active site ‘lock’, initial theory
  • Induced Fit
  • Enzyme active site collides with substrate
  • Flexible enzyme molecule changes shape sightly and moulds to substrate
  • Puts strain on substrate molecules, causing bonds to break or form
  • Suggests charged groups of active site form bonds with substrate molecules securing formation of an ESC
  • More recent and more helpful in explaining enzyme activity
• Activation Energy

  • In chemical reactions energy changes due breaking/forming bonds; exothermic release heat energy (spontaneous, bad) and endothermic absorb heat energy
  • In living organisms, released energy is heat, light, chemical, or electrical
  • Heat and light are lost and cannot be used, but others can
  • Exergonic reactions release energy and endergonic reactions require energy
  • Most reactions require energy input
  • Activation energy
  • Enzymes lower it
  • So reaction proceeds quicker at lower temperatures
• Metabolism

  • All chemical reactions occur in organism
  • Most in cells and use intracellular enzymes, e.g. phagocytic leukocytes, way enzymes are used for defense
  • Sometimes enzymes are secreted to catalyse reactions outside (extracellular) e.g. digestion
  • Organisms such as fungi feed as saprophytes
  • Release digestive enzymes onto large/insoluble food molecules
  • Absorb smaller/soluble products
• Enzyme Examples:

  Conventional to name enzyme by adding -ase, suffix, to derivative of substrate

  A) Cellulase

  B) Glucose

  C) Protease

  D) pepsin

  E) amino acids

  F) polypeptides

  G) lipase

  H) Fatty Acid

  I) Glycerol

  J) lactase

  K) Glucose

  L) Galactose

  M) ATPase

  N) ADP + P_i

  O) Glycogen Synthase

  P) Glycogen

  Q) Catalase

  R) H_2O + O_2

  S) Amylase

  T) Maltose

  
• Cofactors and Co-enzymes

  • Many enzymes only catalyse if a cofactor is also present

  Types:

  • Prosthetic Groups:
  • Permanent
  • Non-protein part of enzyme molecule
  • Contributes to 3D tertiary shape and charges
  • Coenzymes:
  • Small
  • Organic
  • Non-protein
  • Binds temporarily to active site with substrate
  • Many vitamins
  • Vital role in respiration’s enzyme-catalysed reactions
  • Inorganic Ions:
  • Combine with substrate or enzyme (at allosteric site)
  • Affecting charge and shape of ESC so it forms easier