ENZYMES NI SIR

• Enzymes


  • They are catalysts and are not consumed in the reactions
  • They are proteins that act as a catalyst for biochemical reactions
  • The human body has 1000s 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

  
• Enzyme activity


  • It is dramatically affected by alterations in pH
  • It is dramatically affected by temperature
  • It is dramatically affected by other protein denaturants
• Simple enzyme


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


  Has a nonprotein 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
• Cofactors


  Small organic molecules or inorganic ions that are important for the chemically reactive enzymes
• Co-enzymes/co-substrates


  Organic molecule cofactors derived from dietary vitamins
• Inorganic ion cofactors


  • Typical metal ion cofactors - Zn2+, Mg2+, Mn2+, and Fe2+
  • Nonmetallic ion cofactor - Cl-
  • Inorganic ion cofactors derived from dietary minerals
• Substrate


  The reactant in an enzyme-catalyzed reaction
• Enzyme nomenclature


  • Most commonly named with reference to their function
  • Type of reaction catalyzed
  • Identity of the substrate
• Suffix -ase


  Identifies it as an enzyme
• Suffix -in


  Still found in the names of some digestive enzymes
• Oxidase


  Catalyzes an oxidation reaction
• Hydrolase


  Catalyzes a hydrolysis reaction
• Six major classes of enzymes

  • Oxidoreductases
  • Transferases
  • Hydrolases
  • Lyases
  • Isomerases
  • Ligases
• Oxidoreductase


  Catalyzes an oxidation–reduction reaction
• Transferase


  Catalyzes the transfer of a functional group from one molecule to another
• Transaminase


  Catalyzes transfer of an amino group to a substrate
• Kinase


  Catalyzes transfer of a phosphate group from adenosine triphosphate (ATP) to a substrate
• Hydrolase


  Catalyzes a hydrolysis reaction involving the addition of a water molecule to a bond to cause bond breakage
• Carbohydrases


  Hydrolyze glycosidic bonds in oligo- and polysaccharides

  
• Proteases


  Effect the breaking of peptide linkages in proteins
• Lipases


  Effect the breaking of ester linkages in triacylglycerols
• Lyase


  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

  
• Dehydratase


  Effects the removal of the components of water from a double bond
• Hydratase


  Effects the addition of the components of water to double bonds
• Isomerase


  Catalyzes the isomerization (rearrangement of atoms) reactions
• Ligase


  Catalyzes the formation of a bond between two molecules involving ATP hydrolysis
• Active site


  A relatively small part of an enzyme's structure that is actually involved in catalysis
• Enzyme-substrate complex


  Intermediate reaction species formed when substrate binds with the active site
• Lock-and-key model


  Enzyme has a pre-determined shape for the active site, only substrate of specific shape can bind
• Induced fit model


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

  
• Absolute specificity


  An enzyme will catalyze a particular reaction for only one substrate
• Stereochemical specificity


  An enzyme can distinguish between stereoisomers
• Group specificity


  Involves structurally similar compounds that have the same functional groups
• Linkage specificity


  Involves a particular type of bond irrespective of the structural features in the vicinity of the bond
• Higher temperature


  Results in higher kinetic energy which causes an increase in number of reactant collisions, therefore there is higher enzyme activity
• Optimum temperature


  Temperature at which the rate of enzyme catalyzed reaction is maximum