How can enzymes act as catalyst?

Enzymes are complex proteinous substances, produced by living bodies, such as act as catalysis in the physiological reactions. The enzymes are, also called biochemical catalysts and the phenomenon is known as bio-chemical catalysis because numerous reactions that occur the bodies of animals and plants to maintain the life process are catalyzed by enzymes. Though enzymes are produced by living beings, they themselves are non-living and can act as catalysts even outside the living bodies. Enzymes are proteins with high molar mass ranging from 15000 to 1,000,000 g mol-1. Enzymes possess very high catalytic activity. They can increase rates of the reaction by 108 to 1020 times. The enzymes are extremely specific in nature. There is always a lock and key relationship between substrate (reactants) and enzymes. Due to this relationship between the substrate molecules can get attached to the enzyme molecule and then the reaction takes place. Enzymes are capable of bringing about complex reaction at body temperature.

Mechanism of enzyme activity

The stepwise mechanism of enzyme catalyzed reaction as proposed by Michaeli and Menten (1913) is being described as follows.

The reactant molecule attaches itself to the active site on the surface of enzyme. The active site in the given enzyme is so shaped that only a specific substrate can fit in it, just as a lock can be opened only with a specific key. The specific binding results in the creation of enzyme-substrate complex which is also referred to as activated complex.

In the complex, the substrate is located in the proper orientation to assist the chemical reaction and enhancing its rate. The complex finally decomposes to give products and regenerated enzymes. The general reaction system can be presented as:

Step I: binding of substrate (S) to enzyme

1205_enzyme catalysis.png 

Step II: product formation of the complex

[ES]  651_enzyme catalysis3.png  [EP]

Step III: release of the product from the enzyme

1981_enzyme catalysis1.png 

Characteristics of enzyme catalysis

The important characteristics of enzymes catalysts are:
High efficiency: enzyme catalysis increases the speed of reactions by 108 to 1020 times as compared to the uncatalysed reactions.
Extremely small quantities: extremely small quantities of enzyme catalysts - as small as millionth of a mole - can increase the rate of reaction by factors of 103 to 106.
Specificity: the enzyme catalysts are very much specific in nature. This means that one enzyme cannot catalyse more than one process. Almost every biochemical reaction is controlled by its own specific enzymes. For instance, the enzyme urease catalyses the hydrolysis of urea only and  does not catalyse hydrolysis of any other amide. At the same time, none of the several thousand other enzymes present in the cell can catalyse hydrolysis of urea.

473_enzyme catalysis2.png 

In the same manner, Maltase catalyses the hydrolysis of maltose and no other enzyme can catalyse its hydrolysis.
Optimum temperature and pH: the temperature at which enzyme activity is maximum is referred to as optimum temperature. The optimum temperature for enzyme activity is 37°C (310 K). The enzyme activity decreases on either side of optimum temperature. Similarly enzymes catalyzed reaction have maximum rate at pH around 7. Which is also called optimum pH value.
Enhancement of enzyme activity: Catalytic activity of enzymes is greatly enhanced by the presence of activators or co-enzymes. Activators are metal ions (Na+, Mn2+, CO2+, Cu2- etc) which get weakly bonded to enzyme molecules and therefore, promote their catalytic action. For example, the enzyme amylase shows high catalytic activity in the presence of NaCl which provides Na+ ions. Coenzymes are non-protein organic compounds which are required by certain enzymes for their catalytic activity.

   Related Questions in Chemistry

  • Q : Benzoic acid is weaker than paranitro

    Briefly state that Benzoic acid is weaker than paranitro benzoic acid?

  • Q : Explain gels and its various categories.

    Certain sols have the property of setting to a semi-solid, jelly-like form by enclosing the entire amount of liquid within itself when they are present at high concentrations. This process is called gelation and colloidal systems with jelly-like appearance are known as gels. Some common examples

  • Q : Problem on thermodynamic equilibrium In

    In the manufacture of sulphuric acid by the contact process, S02 is oxidized to SO3 over a vanadium catalyst: The reactor is adiabatic and operates at atmospheric pressure. The gases enter the reactor at 410&d

  • Q : Atmospheric pressure Give me answer of

    Give me answer of this question. The atmospheric pressure is sum of the: (a) Pressure of the biomolecules (b) Vapour pressure of atmospheric constituents (c) Vapour pressure of chemicals and vapour pressure of volatile (d) Pressure created on to atmospheric molecules

  • Q : Mole fraction in vapours Choose the

    Choose the right answer from following. If two substances A and B have P0A P0B= 1:2 and have mole fraction in solution 1 : 2 then mole fraction of A in vapours: (a) 0.33 (b) 0.25 (c) 0.52 (d) 0.2

  • Q : Why acetic has less conductivity than

    Illustrate the reason, why acetic has less conductivity than Hcl?

  • Q : Henry law question Answer the following

    Answer the following qustion. The definition “The mass of a gas dissolved in a particular mass of a solvent at any temperature is proportional to the pressure of gas over the solvent” is: (i) Dalton’s Law of Parti

  • Q : Colligative property problem Which is

    Which is not a colligative property: (a) Refractive index (b) Lowering of vapour pressure (c) Depression of freezing point (d) Elevation of boiling point    

  • Q : Explain the preparation of phenols. The

    The methods used for the preparation of phenols are given below:    From aryl sulphonic acids

  • Q : Problem on mol fraction of naphthalene

    At 20°C the solubility of solid naphthalene in hexane is 0.09 mol/mol of solution. Use this information and the data below to estimate the following for this system: a) The mol fraction of naphthalene in the vapour phase in equ

©TutorsGlobe All rights reserved 2022-2023.