CHY47

• Enzymes


  Catalytic proteins
• Enzymes are best known for their catalytic role
• Almost every chemical reaction in the body is driven by an enzyme
• Enzymes


  • Globular proteins
  • Tertiary structure important (bent and folded into spherical or globular shape)
  • Soluble in water
  • Most enzymes are globular proteins
• Enzymes


  Biological catalysts that speed up the rate of the biochemical reaction
• Enzyme catalytic power


  • Catalysts are substances that speed up the rate of a chemical reaction
  • Enzymes cause cellular reactions to occur millions of times faster than corresponding uncatalyzed reactions
  • Enzymes can increase the rate of a reaction by a factor of up to 1020 over uncatalyzed reactions
• An enzyme alters the rate of a reaction, but not its free energy change or position of equilibrium
• Activation energy


  An input of energy before molecules will react together
• Enzymes are not consumed (reusable)
• Active site


  Special pocket or cleft in enzyme molecules where the substrate/s in biochemical reactions attach
• Substrate


  Reactant/s in biochemical reactions

  
• Enzyme-substrate complex


  Forms when the substrate binds to the enzyme's active site

  
• Holoenzymes


  Enzymes with both a protein part (apoenzyme) and a non-protein part (cofactor/coenzyme)

  
• Apoenzymes


  The protein part of an enzyme, unable to bind to its substrate without the required cofactor
• Cofactor


  Non-protein, inorganic substances (metals or ions) bound within the enzyme molecule
• Coenzyme


  Small organic molecules acting as carrier molecules, either as co-substrates (bind transiently) or prosthetic groups (bind tightly)
• Collagen contains hydroxylysine and hydroxyproline, and their hydroxylation is catalyzed by enzymes requiring ascorbic acid (Vitamin C)

  
• Enzyme nomenclature/naming


  • Retain old traditional names
  • Name from the species of origin
  • Use the suffix "-ase" to identify as an enzyme
  • Name based on the function/reaction rather than structure
  • Systematic naming using the Enzyme Commission (EC) number system
• Enzyme classes


  • Oxidoreductases
  • Transferases
  • Hydrolases
  • Lyases
  • Isomerases
  • Ligases/Synthetases

  
• Oxidoreductases


  • Catalyze oxidation or reduction reactions
  • Oxidases catalyze oxidation
  • Reductases catalyze reduction
  • Dehydrogenases catalyze removal or addition of hydrogen atoms
• Transferases


  • Catalyze the transfer of functional groups between donor and acceptor molecules
  • Examples: Kinases, Transaminases, Transmethylases, Transpeptidases, Transacylases
• Hydrolases


  • Catalyze hydrolysis reactions where water is the acceptor of the transferred group
  • Examples: Proteases, Carbohydrases, Lipases, Nucleases, Phosphatases
• Lyases


  • Cleave various bonds by means other than hydrolysis and oxidation
  • Add or remove water, ammonia or carbon dioxide across double bonds
• Isomerases


  • Catalyze isomerization changes within a single molecule
  • Examples: Racemases, Mutases, Epimerases
• Ligases/Synthetases


  • Join two molecules with covalent bonds
  • Require chemical energy (e.g. ATP)
• Specificity


  The ability of an enzyme to choose the exact substrate from a group of similar chemical molecules, through a molecular recognition mechanism

  
• Lock and key theory

  The active site in the enzyme has a fixed, rigid geometrical conformation/shape which is complementary to the substrate

  
• Induced fit theory


  The active site can undergo small changes in shape or geometry to accommodate the substrate
• The forces that draw the substrate into the active site and maintain the enzyme's tertiary structure are hydrogen bonds, hydrophobic interactions, and ionic/electrostatic interactions

  
• Lock and key theory

  Postulated in 1894 by Emil Fischer
• Lock and key theory

  • Active site
  • Enzyme
• Induced fit model


  More thorough explanation for the active-site properties of an enzyme because it includes the specificity of the lock-and-key model coupled with the flexibility of the enzyme protein
• Induced fit model


  Suggested by Daniel Koshland in 1958
• Induced fit model


  • Allows for small changes in the shape or geometry of the active site of an enzyme to accommodate a substrate
  • The forces that draw the substrate into the active site are the same forces that maintain tertiary structure in the folding of peptide chains (hydrogen bond, hydrophobic interaction, ionic/electrostatic interaction or salt bridges)

  
• Specificity


  • The ability of an enzyme to choose exact substrate from a group of similar chemical molecules
  • Molecular recognition mechanism that operates through the structural and conformational complementarity between enzymes and substrate

  
• Types of enzyme specificity

  • Stereo (Stereochemical) specificity
  • Substrate (Absolute) specificity
  • Group specificity
  • Bond (Relative) specificity
  • Geometrical specificity

  
• Geometrical specificity is the least specific, single enzyme can act on different substrates having similar molecular geometry
• Relative or linkage specificity

  The enzyme will act on a particular type of chemical bond, irrespective of the rest of the molecular structure
• Relative or linkage specificity

  • Phosphatases hydrolyze phosphate-ester bonds in all types of phosphate esters
  • Proteinases (peptidases member of the group of proteinases) hydrolyze peptide bonds
• Group specificity


  • The enzyme will act only on molecules that have a specific functional group, such as hydroxyl, amino, or phosphate groups
  • Moderate specificity (More than that of bond specificity)