enzymes

• Simple enzyme


  Made up of only protein molecules not bound to any non-proteins
• Enzymes

  • They are protein catalysts for chemical reactions in biological systems
  • They increase the rate of chemical reactions within living cells without being changed or consumed
• All cellular reactions have a high energy barrier and proceed too slowly, enzymes lower this energy barrier required for cell survival
• Apoenzyme


  The protein component of a holo enzyme
• Isoenzymes (Isozymes)


  Enzymes having similar catalytic activity, act on the same substrate and produce the same product but originated at different sites and exhibit different physical and chemical characteristics
• Cofactor

  If the non-protein component of the holo enzyme is an inorganic group
• Rate Limiting Steps are the slowest steps in a reaction that set the pace for the entire reaction
• Enzymes are important in the human body because many reactions required for the living cell would not proceed fast enough at the pH and temperature of the body without enzymes
• Holo enzyme


  Made up of protein groups and non-protein component
• Unwanted reactions would never occur spontaneously due to the high energy barrier
• Active site


  • Special pocket or cleft in enzyme molecules where substrate binding and catalysis occur
• Coenzyme


  If the non-protein component of the holo enzyme is an organic compound
• Prosthetic group


  If the non-protein part is bound tightly to the apoenzyme and is difficult to remove without damaging the enzyme
• Isoenzymes


  • LDH (Lactate dehydrogenase) exists in five different forms each having four polypeptide chains: LDH-1, LDH-2, LDH-3, LDH-4, LDH-5
• Enzyme-substrate interaction

  1. Substrate binds the enzyme non-covalently to form an enzyme–substrate (ES) complex

  2. ES is converted to an enzyme–product (EP) complex that dissociates to enzyme and product
• The enzyme-substrate binding is now viewed as the induced-fit model where the binding and active sites are not fully pre-shaped
• Enzyme activity can be regulated to respond to cellular needs, controlling metabolic functions like energy storage and release, maintaining blood glucose levels, digestion, absorption of nutrients, and formation of complex molecules
• Most enzyme-catalyzed reactions are highly efficient, proceeding from 10^3 to 10^8 times faster than uncatalyzed reactions
• Enzymes are highly specific, interacting with one or a few substrates and catalyzing only one type of chemical reaction
• Each enzyme molecule is capable of transforming 100 to 1000 substrate molecules into product each second
• The substrate binds to the enzyme through reversible interactions formed by Hydrogen bonds and Hydrophobic interactions
• Interaction of substrate with enzyme induces a conformational change in the enzyme, resulting in the formation of a stronger binding site and repositioning of appropriate amino acids to form the active site
• Specificity of enzymes

  • Absolute specificity
  • Bond Specificity
• Many enzymes are localized in specific organelles within the cell to isolate reaction substrates or products from other competing reactions, providing a favorable environment for the reaction and organizing enzymes into purposeful pathways