E&V

• Enzyme


  An organic compound that acts as a catalyst for a biochemical reaction
• Enzymes govern all biological chemical reactions. They catalyze biological reactions with fascinating precision and selectivity. They store and release energy, make pigments in our hair and eyes, digest the food we eat, synthesize cellular building materials, and protect us by repairing cellular damage and clotting our blood.
• Bread dough rises as the result of carbon dioxide production resulting from the action of yeast enzymes on sugars present in the dough
• Enzymes


  • They are catalysts and are not consumed in the reactions
  • They are specialized proteins that act as a catalyst for biochemical reactions and cause cellular reactions to occur millions of times faster
  • The human body has thousands of enzymes
  • They are the most effective catalysts known
  • Most enzymes are globular proteins
  • A few enzymes are now known to be ribonucleic acids (RNA)
  • They undergo all the reactions of proteins including denaturation
  • Their activity is dramatically affected by alterations in pH, temperature, and other protein denaturants

  
• Simple enzyme


  Composed only of protein (amino acid chains)
• Conjugated enzyme


  Has a non-protein part in addition to a protein part
• Apoenzyme


  Protein part of a conjugated enzyme
• Cofactor


  Nonprotein part of a conjugated enzyme
• Holoenzyme


  The biochemically active conjugated enzyme (apoenzyme + cofactor)

  
• Cofactors


  • They provide additional chemically reactive functional groups besides those of the side chains of the amino acids in the apoenzyme
  • They can be small organic molecules (also called co-enzymes or co-substrates) derived from dietary vitamins
  • They can be inorganic ions like Zn2+, Mg2+, Mn2+, Fe2+, and Cl- derived from dietary minerals
• Substrate


  The reactant in an enzyme-catalyzed reaction, the substance upon which the enzyme "acts"

  
• Most commonly, enzymes are named with reference to their function (type of reaction catalyzed) and the identity of the substrate

  
• Six major classes of enzymes based on the types of reactions they catalyze


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

  
• Oxidoreductase


  An enzyme that catalyzes an oxidation–reduction reaction, requiring a coenzyme that is either oxidized or reduced as the substrate
• Oxidoreductase subclasses


  • Oxidases
  • Reductases
  • Dehydrogenases
• Transferase


  An enzyme that catalyzes the transfer of a functional group from one molecule to another
• Transferase subclasses


  • Transaminases
  • Kinases
• Hydrolase


  An enzyme that catalyzes a hydrolysis reaction, involving the addition of a water molecule to a bond to cause bond breakage
• Hydrolase subclasses


  • Lipases
  • Proteases
  • Nucleases
  • Carbohydrases
  • Phosphatases
• Lyase


  An enzyme that catalyzes the addition of a group to a double bond or the removal of a group to form a double bond in a manner that does not involve hydrolysis or oxidation
• Lyase subclasses


  • Hydratases
  • Dehydratases
  • Decarboxylases
  • Deaminases
• Isomerase


  An enzyme that catalyzes the isomerization (rearrangement of atoms) of a substrate converting it to a molecule isomeric with itself

  
• Isomerase subclasses


  • Racemases
  • Mutases
• Ligase


  An enzyme that catalyzes the formation of a bond between two molecules involving ATP hydrolysis
• Ligase subclasses


  • Synthetases
  • Carboxylases
• Maltase hydrolyzes maltose, lactate dehydrogenase removes hydrogen from lactate ion, fructose oxidase oxidizes fructose, and maleate isomerase rearranges the maleate ion
• Hexokinase is a transferase that catalyzes the transfer of a phosphate group from ATP to glucose
• Fumarase is a lyase that catalyzes the addition of water to fumarate to form L-malate
• Phosphoglyceromutase is an isomerase that catalyzes the rearrangement of 3-phosphoglycerate to 2-phosphoglycerate
• Pyruvate carboxylase is a ligase that catalyzes the formation of oxaloacetate from pyruvate and CO2, with the participation of ATP
• Active site


  Relatively small part of an enzyme's structure that is actually involved in catalysis, where the substrate binds

  
• Active site


  • It is a "crevice-like" location in the enzyme
  • Some enzymes have more than one active site

  
• Enzyme-substrate complex


  The intermediate reaction species formed when the substrate binds with the active site

  
• Lock-and-key model


  The enzyme has a pre-determined shape for the active site, and only a substrate of specific shape can bind

  
• Induced fit model


  Substrate contact with the enzyme will change the shape of the active site to accommodate the substrate

  
• Forces that determine substrate binding


  • Hydrogen bonding
  • Hydrophobic interactions
  • Electrostatic interactions
• Absolute specificity


  An enzyme will catalyze a particular reaction for only one substrate

  
• Stereochemical specificity


  An enzyme can distinguish between stereoisomers due to the chirality inherent in the active site
• Group specificity


  An enzyme can catalyze reactions of structurally similar compounds with the same functional groups
• Linkage specificity


  An enzyme can catalyze the hydrolysis of a particular type of bond irrespective of the structural features in the vicinity of the bond