Enzymes

                                      Enzymes

        Metabolism....
          -sum of all biological activities in body 
                  -mainly ;
                                   a)anabolism       b) catabolism
                   
                    Anabolism
                    formation of COMPLEX molecules from simpler molecules
                    with aid of ENERGY.
                    Catabolism
                    Breakdown of complex molecules into simpler molecules through
                    HYDROLYSIS or OXIDATION and the release of energy.

                    #In form 5 we learnt about endothermic and exothermic reactions , similarly
                       now we call it exogonic (reactions that liberate more energy than it takes in)
                       and endergonic (reactions that takes in more energy than it liberates)

                    #Such metablic reactios are catalysed by enzymes .

                   .

                Enzymes... biological catalysts 

              # Enzymes are PROTEIN CATALYSTS that speed up metabolic reactions.
                        # Enzymes are GLOBULAR PROTEIN with PRECISE  3-D shape that are                     
                           composed of primary,secondary,tertiary and probably Quaternary stuctures
                        # Each enzyme has an active site which can bind with one or more substrate 
                           which is a cleft or located deeper within the enzyme.

                        
                      # The active site of enzyme can be bound by a certain substrate.
                      # The active site has a specific shape due too the side chains of amino acids

                      ***Some enzymes have ALLOSTERIC sites : sites when certain chemicals are
                           attached can either slow down or speed up reactions.

                   Mode of action of enzymes

             # Enzymes lowers activation energy of reactions by ;

  

                   ~Forming enzyme-substrate complex.

                   ~Weakening bonds of substrate.

                   ~Forming new bonds in substrate molecules

                   ~Bringing two substrate molecules close together .

                   ~Orienting two substrate molecules to react

                   ~Providing correct environment for reaction too occur.

Activation energy -The minimum amount of energy required for reactants to reach transition state before becoming products 

Lock and Key model.

The hypothesis proposed that the active site and substrate are complementary too each other.

                      A)substrate is smaller than enzyme     

B)enzyme is bigger with rigid active site

                      C)substrate fits into the active site complementarily 

                      D)enzyme-substrate is formed (reversible)

                      E)Substrate is converted into products

                      F)products is then released as it no longer fits the     

                         active site of enzyme. 

                      Induced fit model

                

                   -Active site of enzyme is larger (but still specific), substrate binds with active site complimentarily which causes the enzyme too mould around it causing it to stress.Bonds are formed between substrate and products ( especially H+ bonds) while other bonds are broken by the enzyme. Finally the substrate is converted into products and  leaves the enzyme.

Time course of enzyme catalyzed reactions.

• The rate of enzyme catalyzed reaction is taken as initial velocity.
• It is measure by the Rate of change of substrate/rate of formation of products over Period of time.
•  The steeper the slope the higher the rate of reaction.
• The reaction is fastest at the beginning of reaction.
• Over time, the rate of reaction slows down as a result of decrease of concentration of substrate.

Michealis-Menten Constant (Km)

Canadian physician Maud Menten formed an equation about rate of reaction of enzymes , by relating reaction rate  and the substrate concentration.

A=enzyme  

  E=Substrate

                            B= enzyme-substrae complex

C=product

E=Product

The Michaelis Menten equation shows how velocity varies with substrate concentration;