Enzymes

• Enzymes are biological catalysts that increase the rate of metabolic reactions in living organisms without being used up or changed. They turn substrate into products.
• Define the Turnover number:

  the number of reactions that an enzyme can catalyse per second
• Enzymes work best at their optimum...

  • temperature (kinetic energy)
  • pH
• Define Active site:

  A highly specific indentation on the surface of enzymes that is complementary to specific substrates
• Biological catalysts are more specific and do not produce unwanted by-products
• Intracellular enzymes catalyse reactions in the cell
• Intracellular enzymes are used in a metabolic pathway
• Metabolic pathway:

  a series of consecutive reactions
• The reactants, intermediates, and products involved in a metabolic pathway are called metabolites
• State two examples of metabolic pathways:

  • respiration
  • photosynthesis
• Describe catalase:

  • intracellular enzyme
  • four polypeptide chains
  • a haem group with iron
  • function: protects cells from damage from reactive oxygen by breaking down hydrogen peroxide
  • humans: 45 °C / pH 7
  • others: 90 °C / pH 4 - 11
  • the highest turnover number known- 6 million per second ∴ fastest acting enzyme
  • found in peroxisomes in eukaryotic cells
  • functions: when white blood cells ingest pathogens they use catalase to help kill the invading microbe
• Extracellular enzymes are secreted from the cell so catalyse reactions outside the cell
• State four extracellular enzymes:

  • hydrolytic
  • amylase (digestives)
  • trypsin (digestives)
• Enzyme amylase and trypsin are both made in the pancreas
• Enzyme amylase is made in the pancreas and salivary glands
• Enzyme amylase and trypsin are both found in the small intestine
• Enzyme trypsin digest protein
• Enzyme amylase are found in the mouth and the small intestine
• The substrate for amylase is starch
• Define Co-factors:

  a substance attached to enzymes to ensure catalysed reactions take place at the appropriate rate
• Co-factors can act as a prosthetic group; for example, zinc 2+ ions attached to carbonic anhydrase, and Cl- as a co-factor, attached to amylase
• carbonic

  anyhydrase

  CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-
• Carbonic anhydrase are found in erythrocytes (red blood cells)
• ⇌ : the reaction can happen in either direction depending on the concentration of substrates or products
• Carbonic anhydrase are important because it enables CO2 to be carried in the blood from respiring tissues / cells to the lungs
• Enzymes work better when ions are present.
• Define Co-enzymes:

  Organic non protein molecules that bind temporarily to change active sites during a reaction
• What happens after a co enzyme changes an active site?

  a different enzyme recycles the active site back to its original shape
• State the two types of metabolic pathways:

  • catabolic
  • anabolic
• In catabolic pathways, larger molecules are broken down into smaller molecules and release energy
• In anabolic pathways, energy is used to synthesise larger molecules from smaller ones
• Many co-enzymes are derived from water soluble vitamins
• If vitamins are deficient in diet, certain diseases may result.
• Name six co-enzymes:

  • cobalamin
  • tetrahydrofolate
  • NAD
  • NADP
  • coenzyme A
  • thiamine pyrophosphate
• Cobalamin coenzymes are derived from vitamin B12

  Human deficiency disease: pernicious anaemia
• tetrahyrofolate coenzymes are derived from vitamin B9 - folic acid

  Human deficiency disease: megablastic anaemia
• NAD & NADP coenzymes are derived from vitamin B3 - nicotinamide

  Human deficiency disease: pellagra
• Coenzyme A is derived from vitamin B6 - pantothenate

  Human deficiency disease: elevated blood plasma triglyceride levels
• Thiamine pyrophosphate coenzymes are derived from vitamin B1 - thiamine

  Human deficiency disease: beriberi
• What does megablastic anaemia cause?

  large irregularly shaped erythrocytes (red blood cells)