chemlec enyzmes

• 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 (apoenzyme + cofactor)

  
• Cofactors


  • They are important for the chemically reactive enzymes
  • They are small organic molecules or Inorganic ions
  • Organic molecule cofactors are also called as co-enzymes or co-substrates
  • Co-enzymes/co-substrates are derived from dietary vitamins
  • Inorganic ion cofactors include typical metal ions like Zn2+, Mg2+, Mn2+, and Fe2+, and the nonmetallic ion Cl-
  • Inorganic ion cofactors are derived from dietary minerals
• Nomenclature of enzymes


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


  The reactant in an enzyme-catalyzed reaction
• Enzyme naming process


  • Suffix -ase identifies it as an enzyme
  • Type of reaction catalyzed by an enzyme is often used as a prefix
  • Identity of substrate is often used in addition to the type of reaction
• Oxidoreductase


  An enzyme that catalyzes an oxidation–reduction reaction
• Transferase


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


  A transferase that catalyzes transfer of an amino group to a substrate
• Kinase


  A transferase that catalyzes transfer of a phosphate group from adenosine triphosphate (ATP) to a substrate

  
• Hydrolase


  An enzyme that catalyzes a hydrolysis reaction
• Carbohydrase


  A hydrolase that hydrolyzes glycosidic bonds in oligo- and polysaccharides

  
• Protease


  A hydrolase that effects the breaking of peptide linkages in proteins
• Lipase


  A hydrolase that effects the breaking of ester linkages in triacylglycerols
• 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

  
• Dehydratase


  A lyase that effects the removal of the components of water from a double bond

  
• Hydratase


  A lyase that effects the addition of the components of water to double bonds
• Isomerase


  An enzyme that catalyzes the isomerization (rearrangement of atoms) reactions
• Ligase


  An enzyme that catalyzes the formation of a bond between two molecules involving ATP hydrolysis
• Enzyme active site


  • It is a relatively small part of an enzyme's structure that is actually involved in catalysis
  • It is the place where substrate binds to enzyme
  • It is formed due to folding and bending of the protein
  • It is usually a "crevice like" location in the enzyme
  • Some enzymes have more than one active site
• Enzyme-substrate complex


  An 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, allowing small changes to accommodate substrate
• Forces that determine substrate binding

  • H-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
• 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
• Effect of temperature on enzyme activity

  • Higher temperature results in higher kinetic energy which causes an increase in number of reactant collisions, therefore there is higher activity
  • Optimum temperature is the temperature at which the rate of enzyme catalyzed reaction is maximum
  • Optimum temperature for human enzymes is 37ºC (body temperature)
  • Increased temperature (high fever) leads to decreased enzyme activity
• Effect of pH on enzyme activity

  • pH changes affect enzyme activity
  • Drastic changes in pH can result in denaturation of proteins
  • Optimum pH is the pH at which enzyme has maximum activity
  • Most enzymes have optimal activity in the pH range of 7.0 - 7.5
  • Digestive enzymes have different optimum pH values, e.g. Pepsin: Optimum pH = 2.0, Trypsin: Optimum pH = 8.0

  
• Effect of substrate concentration on enzyme activity

  • At a constant enzyme concentration, the enzyme activity increases with increased substrate concentration
  • Substrate saturation is the concentration at which it reaches its maximum rate and all of the active sites are full
  • Turnover number is the number of substrate molecules converted to product per second per enzyme molecule under conditions of optimum temperature and pH
• Effect of enzyme concentration on enzyme activity

  • Enzymes are not consumed in the reactions they catalyze
  • At a constant substrate concentration, enzyme activity increases with increase in enzyme concentration
  • The greater the enzyme concentration, the greater the reaction rate
• Enzyme inhibitor


  A substance that slows down or stops the normal catalytic function of an enzyme by binding to it
• Competitive inhibitor


  Competes with the substrate for the same active site
• Noncompetitive inhibitor


  Does not compete with the substrate for the same active site, binds to the enzyme at a location other than active site