Enzymes

• Enzymes are biological catalyst that speeds up chemical reactions inside a living cell.
• They are proteins therefore they undergo all the reactions of proteins, such as denaturation and coagulation by heat, alcohol, strong acids, and alkaloidal reagents.
• The names of most enzymes end with the suffix -ase.
• Highly increases the rate of the reaction (106 to 1012 times faster), without themselves being changed in the overall process.
• Very specific with the reaction it catalyzed, for example, Lactase will only react with Lactose.
• Formation of side product is rare and they have very complex structure, hence are capable of being regulated
• CLASSIFICATION OF ENZYMES BY SUBTRATE:

  
  

  Based on the what type of molecule they specifically react to. Example: Urease, lactase, and lipase.
• CLASSIFICATION OF ENZYMES: Reaction they Catalyzed

  Oxido-reductases - catalyze oxidation and reduction reactions in which electrons travel from one molecule to another.
• CLASSIFICATION OF ENZYMES: Reaction they Catalyzed

  Transferases catalyze the transportation of a functional group from one molecule to another.
• CLASSIFICATION OF ENZYMES: Reaction they Catalyzed

  Hydrolase enzymes catalyze the hydrolysis of chemical bonds with the action of water (HOH).
• CLASSIFICATION OF ENZYMES: Reaction they Catalyzed

  Lyases catalyze the breakdown of various chemical bonds by means other than hydrolysis and oxidation, often forming new double bonds or ring structures
• CLASSIFICATION OF ENZYMES: Reaction they Catalyzed

  Isomerases catalyze structural shifts in molecules, causing changes in shape.
• CLASSIFICATION OF ENZYMES: Reaction they Catalyzed

  Ligases catalyze ligation--the combination of pairs of substrates.
• Examples of Transferases


  Transaminases (transfer of NH2 group), Kinases (transfer of a phosphate)
• Examples of Hydrolases


  Lipases (lipid esters), Protases (amide bonds in proteins), Nucleases (nucleic acids)
• Examples of Lyases


  Dehydrases (remove H2O), Decarboxylases (remove CO2), Synthases (add small mo. to DB)
• Example of Ligases


  Carboxylases (bond formation between a substrate and CO2)
• Enzymes lowers the activation energy ( energy required for a chemical reaction to

  occur)
• Provides unique binding surface called ACTIVE SITE. Reactant molecule called SUBSTRATE binds to the enzyme’s active site
• •An enzyme contains an active site that binds the substrate, forming an enzyme-substrate complex.
• •Once the reaction has occurred, the catalyst released the product(s).

  A) products

  
• •The lock-and-key model states that the active site is a rigid cavity; to react, the substrate must exactly match the shape of the active site. Proposed by Emil Fischer.
• •The induced-fit model states that the active site has a flexible shape, which can adjust to fit a variety of substrate shapes. Proposed by Daniel Koshland.
• Figure 1: Lock and Key Model by Emil Fischer

  Figure 2: Induced-fit Model by Daniel Koshland.

  
• Catalytic activity of some enzyme depend only on the interaction between the active site and the substrate.
• Other enzymes require non-protein component for their activity, called enzyme cofactors which are ENZYME COFACTORS.
• ENZYME COFACTORS:

  Metal Activators ( Fe+2, Cu+2, Na+ )
• ENZYME COFACTORS:

  Coenzymes (organic molecule needed for an enzyme-catalyzed reaction to occur).
• NAD+ is the cofactor (coenzyme) that oxidizes lactate to pyruvate

  with the aid of the enzyme lactate dehydrogenase:
• •Coenzyme FAD (flavin adenine dinucleotide) is an oxidizing agent as well. Removal of 2 H's.
• Apoenzyme – an enzyme (protein part) that lacks an essential

  cofactor.
• Holoenzymes – intact enzymes with their bound cofactors. Coenzyme + apoenzyme.
• Zymogens -(proenzymes) are an inactive form of an enzyme that can be converted to the active form when needed.
• FACTORS AFFECTING THE RATE OF ENZYME-CATALYZED REACTION:

  1. substrate and enzyme concentration
  2. temperature - Optimum temp.- temp. at which the rate of enzyme’s activity is at maximum.
  3. pH - Optimum pH – pH at which the rate of enzyme’s activity is at maximum
• Figure 1: Rate of reaction is directly proportional to the enzyme concentration. As the amount of enzyme increases, the rate also increases.

  
• Figure 2: Increase in substrate will increase the rate but then stops affecting it when all the active sites are occupied (point of saturation)

  
• Figure 3: As the temperature increase the reaction also increase, but then stops and decreases when optimal temp. (when enzymes are most active) is reached because from then enzymes decreases as they denature.

  
• Figure 4: As the pH increase the reaction also increase, but then stops and decreases when optimal pH (when enzymes are most active) is reached because from then enzymes decreases as they denature.

  
• •An inhibitor bonds to the enzyme and alters or destroys the enzyme’s activity.

  •This inhibition can be reversible or irreversible.
• •A noncompetitive inhibitor bonds to the enzyme, but not to the active site.

  •A competitive inhibitor has a shape and structure similar to the substrate, so it competes with the substrate for binding to the active site.