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 : Problem on equilibrium composition The

    The catalytic dehydrogenation of 1-butene to 1,3-butadiene, C4H8(g) = C4H6(g)+H2(g) is carried out at 900 K and 1 atm.

    Q : Effect on vapour pressure of dissolving

    Give me answer of this question. When a substance is dissolved in a solvent the vapour pressure of the solvent is decreased. This results in: (a) An increase in the b.p. of the solution (b) A decrease in the b.p. of the solvent (c) The solution having a higher fr

  • Q : Coagulation what is the meaning of

    what is the meaning of fourth power of valency of an active ion?

  • Q : Question on colligative property Choose

    Choose the right answer from following. Which of the following is a colligative property: (a) Osmotic pressure (b) Boiling point (c) Vapour pressure (d) Freezing point

  • Q : What are biodegradable polymers?

      These are polymers that can be broken into small segments by enzyme-catalysed reactions. The required enzymes are produced by microorganism. It is a known fact that the carbon-carbon bonds of chain growth polymers are inert to enzyme-catalysed reactions, and hence they are non biod

  • Q : Question based on relative lowering of

    Give me answer of this question. When a non-volatile solute is dissolved in a solvent, the relative lowering of vapour pressure is equal to: (a) Mole fraction of solute (b) Mole fraction of solvent (c) Concentration of the solute in grams per litre

  • Q : Describe First Order Rate Equation The

    The integrated forms of the first order rate equations are conveniently used to compare concentration time results with this rate equation. Rate equations show the dependence of the rate of the reaction on concentration can be integrated to give expressions fo

  • Q : Organic and inorganic chemistry Write

    Write down a short note on the differences between the organic and inorganic chemistry?

  • Q : Entropy is entropy on moleculare basis

    is entropy on moleculare basis relates to the tras.,vib.,and rotational motions?

  • Q : Finding Normality Can someone please

    Can someone please help me in getting through this problem. Concentrated H2SO4 has a density of 1.98 gm/ml and is 98% H2SO4 by weight. The normality is: (a) 2 N  (b) 19.8 N  (c) 39.6 N  (d) 98

©TutorsGlobe All rights reserved 2022-2023.