Enzyme Action:

Ø  Enzyme accelerates the rate of reaction while experiencing no permanent chemical modification as a result of participation.

Ø  Enzymes have active site. This is part of the molecule that has just the right shape and functional groups to bind to one of the reacting molecule. The reacting molecule that binds to the enzyme is called substrate.

Ø  The enzyme catalyze reaction take a different route. The enzymes and substrate form a reaction intermediate. Its formation has lower activation energy than the reaction between reactants without a catalyst.

Ø  For two molecule to react they must collide with one another. They must collide in the right direction with sufficient amount of energy. Energy which is needed to overcome an energy barrier of the reaction is called activation energy.

Route A

                                                        Reactant 1+ Reactant 2                      Product

                                                Route B

                                                      Reactant 1 + Enzyme                         Intermediate

                                                      Intermediate + Reactant 2                         Product + Enzyme

1)      Lock and key hypothesis:

Here substrate simply fits into the active site to form a reaction intermediate.

2)      Induced fit hypothesis:

In this model enzyme molecule changes shape as the substrate molecule gets close. The change in shape is induced by the approaching substrate molecule. This more sophisticated model relies on the fact that molecule are flexible.

Eg : Single covalent bonds are free to rotate.


Inhibition of Enzyme Activity:

Some substrates reduce or even stop the catalytic activity of enzyme in biochemical reaction.  They block or distort the active site of enzyme. These chemicals are called inhibitors because they inhibit the biochemical reaction.

Inhibitors are basically of three types:

                                                        I.Competitive inhibitors

                                                      II.Non-competitive inhibitors

                                                    III.Uncompetitive inhibitors

1)      Competitive inhibitors: Inhibitors that occupy the active site and prevent the substrate molecule from binding to the enzyme’s active site. They are said to be active site directed. They are called competitive because they compete with the substrate for the active sites.

2)      Non-competitive inhibitors: Inhibitors that attach with other parts of enzyme molecule perhaps distorting its shape are said to be non- active site directed or non- competitive inhibitors.

3)      Uncompetitive inhibitors: Uncompetitive inhibitors are differ from competitive inhibitors in that they have a separate binding site on the enzyme. Also they only bind to the enzyme when substrate is bound to the enzyme.


Factors affecting catalytic activity of enzyme:

        I.            Temperature: As temperature rises, reacting molecule have more and more kinetic energy. This increases the chance of collision and so the rate increases. There is a certain temperature at which enzyme’s catalytic activity is at its greatest. This optimal temperature is about 37.5°C for the enzyme in human cells. Above this temperature enzyme structure begins to denature since at higher temperature enzyme breakdown occur.

      II.            p H: Each enzyme works within a certain p H range. This is called as optimal p H range. At this p H range enzyme activity is greatest. Change in p H can make and break intermolecular and intramolecular bonds changing the shape of enzyme and its effectiveness.


    III.            Concentration of enzyme and substrate: Rate of enzyme catalyzed reaction depends on the concentration of enzyme and substrate. As the concentration of either is increased, rate of reaction is increased. For a given enzyme catalyzed reaction, the rate of reaction is increases with increases substrate concentration upto a point, above which any further increases in substrate concentration produce no significant change in reaction rate. This is due to a reason that the active site of enzyme molecule at any given moment is virtually saturated with substrate. The E-S complex has to dissociate before the active site are free to accommodate more substrate.

Function of enzyme:

1)      Enzymes are biological catalysts. Biological means the substance is derived from some living organism. Catalyst is a substance that has ability to increase the rate of chemical reaction and is not changed or destroyed by the chemical reaction that is accelerated. They speed up the rate at which reactants interact to form product in a chemical reaction while not being consumed in the reaction.

2)      Enzymes are major components in signal transduction and cell regulation. Phosphatases and Kinases help in this function.

3)      Myosin (muscle protein) helps in muscle contraction in living organisms.

4)      ATPases in the cell membrane act as a ion pump in active transport mechanisms

5)      Enzymes play a role in the digestive activity of the enzyme.

6)      Amylases and Proteases are enzyme that break carbohydrate (amylase) and protein in its   simpler absorbable forms.

7)      Various enzymes work together in a order forming metabolic pathways. Eg : Glycolysis

8)      ATPases in the cell membrane act as ion pumps in active transport mechanisms

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