ENZYMES AND CARBS

• Enzymes are not another biomolecule but a protein
• Enzyme


  Catalyst for biochemical reactions
• Enzymes

  • They make the reaction faster
  • They remain unchanged
• Enzymes are not another biomolecule but a protein
• Enzyme


  Catalyst for biochemical reactions
• Enzymes


  • They make the reaction faster
  • They remain unchanged
• Enzymes undergo all the reactions of proteins, including denaturation
• There are thousands of enzymes in the human body, each reaction is accompanied with an enzyme
• Classes of enzymes


  • Simple enzyme (protein only)
  • Conjugated enzyme (nonprotein part + protein part)
• Apoenzyme


  Protein part of the conjugated enzyme
• Cofactor


  All non protein parts of a conjugated enzyme
• Holoenzyme


  Biochemically active part of the conjugated enzyme
• Types of cofactors


  • Small organic molecules (derived from dietary vitamins)
  • Inorganic ions (derived from dietary minerals)
• Substrate


  Reactant in an enzyme-catalyzed reaction, substance upon which the enzyme acts and is converted into product
• Enzyme naming conventions

  • Suffix -ase (identifies as enzyme)
  • Suffix -in (found in names of digestive enzymes)
  • Type of reaction (e.g. oxidase, hydrolase)
  • Identity of substrate (first name of enzyme)
  • General nature of substrate (e.g. lipase, protease)
• Systematic nomenclature of enzymes


  Developed by International Union of Biochemistry and Molecular Biology (IUBMB), enzymes are subdivided into 6 molecular classes
• 6 major classes of enzymes


  • Oxidoreductases (catalyze oxidation-reductions)
  • Transferases (catalyze functional group transfer reactions)
  • Hydrolases (catalyze hydrolysis reactions)
  • Lyases (catalyze reactions involving addition or removal of groups from double bonds)
  • Isomerases (catalyze isomeration reactions)
  • Ligases (catalyze reactions involving bond formations coupled with ATP hydrolysis)
• Active site


  • Asymmetric pocket where biological reactions are catalyzed
  • Contains amino acid side chains that create 3-dimensional surface complementary to the substrate
• Enzyme-substrate complex


  Intermediate reaction species formed when substrate binds with the active site

  
• Fischer mechanism (Lock and Key Model)


  Substrate is fixed in shape to the active site before binding, perfect match
• Koshland mechanism (Induced-fit Model)


  The active site and substrate do not match in shape before binding, the active site adapts to the substrate whilst binding

  
• Enzyme properties


  • Catalytic efficiency (103-108 times faster than uncatalyzed reactions)
  • Specificity (highly specific, interacts with one or few substrates, catalyzes only one type of chemical reaction)
  • Cofactors (non protein portion needed for enzymic activity)
  • Regulation (can be activated or inhibited)
  • Location within the cell (most are localized within specific organelles)

  
• Reaction velocity


  Number of substrate molecules converted to product per unit time, expressed as μmol of product formed per minute
• Factors affecting reaction velocity


  • Temperature (optimum 37°C, increased temperature leads to denaturation)
  • pH level (optimum 7.0-7.5, digestive enzymes have different optima)
  • Substrate concentration (higher concentration increases velocity up to saturation)
  • Enzyme concentration (directly proportional)
  • Cofactors (affect proper functioning)
  • Inhibitors (substances that diminish velocity)

  
• Free energy of activation

  Energy difference between reactants and high-energy intermediate during product formation, lower activation energy increases reaction rate

  
• Michaelis-Menten equation


  Describes how reaction velocity varies with substrate concentration, Km = 1/2 Vmax, small Km means high enzyme affinity for substrate

  
• Lineweaver-Burk plot


  Double-reciprocal plot used to calculate Km and Vmax, determine mechanism of enzyme inhibitors

  
• Enzyme inhibitor


  Substance that slows down or blocks enzyme-catalyzed reactions
• If the reactant peak is low and the energy peak is significantly higher


  • The reactants will not be converted into products or there will be fewer reactants converted

  
• ↓ free energy of activation

  ↑ molecules that have sufficient energy to pass through transition state, ↑ rate of reaction

  
• MICHAELIS-MENTEN EQUATION


  Describes how reaction velocity varies with substrate concentration

  
• V0


  Initial velocity
• Vmax


  Highest maximum velocity
• Km


  Michaelis-Menten Equation
• Km


  ½ Vmax
• Small Km


  Enzyme has high affinity for substrate
• Large Km


  Enzyme has low affinity for substrate
• []


  Concentration in molarity
• LINWEAVER-BURK PLOT


  Double-reciprocal plot, Used to calculate Km and Vmax, Determine the mechanism of action of enzyme inhibitors, Inhibitor can be identified with the graph that was used

  
• ENZYME INHIBITOR


  Substance that slows down or stops the normal catalytic function of an enzyme by binding to it