12.1 Characteristics of Enzymes

2.1 Characteristics of Adsorption
2.2 Types of Adsorption

4.1 Freundlich adsorption isotherm
4.2 The Langmuir adsorption isotherm

7.1 Different Colloidal Systems
7.2 Classification of Colloidal System
7.3 Preparation of Colloidal System
7.4 Purification of Colloidal System
7.5 Properties of colloidal system

8.1 Protective colloids

9.1 Foams
9.2 Applications of colloids and emulsions

10.1 Positive and negative catalysis
10.2 Types of catalysis

12.1 Characteristics of Enzymes
12.2 Mechanism of enzyme catalysis
12.3 Autocatalysis
12.4 Induced catalysis

Each enzyme catalyses only one chemical reaction.

Question 5. Explain the specificity of unease with reactions.

Solution: The enzyme urease hydrolyses urea to $N{H_3}$ and $C{O_2}$ but it does not catalyse the hydrolysis of N-methylurea which is similar in constitution to urea.

\[\begin{array}{c}{N{H_2}CON{H_2}}& + &{{H_2}O} \end{array}\begin{array}{c}{\xrightarrow{{Urease}}}&{2N{H_3}} \end{array}\begin{array}{c}+ &{C{O_2}} \end{array}\]

\[\begin{array}{c}{C{H_3}NHCON{H_2}}& + &{{H_2}O} \end{array}\begin{array}{c}{\xrightarrow{{Urease}}}&{No\;action} \end{array}\]

Enzymes are very efficient catalysts. They speed up the rate of a reaction by factors of upto ${10^{20}}$. To get an idea about the tremendous efficiency of enzymes, let us consider the hydrolysis of amides.

Amide bonds are chemically very stable. That is why, hydrolysis of amides in the laboratory requires the heating of amides with an alkali for a few hours. In contrast, proteins present in our food, which also contain amide (peptide) bonds, are easily hydrolyzed in our body by different enzymes to individual alpha amino acids.

Enzyme catalysed reactions have maximum rate at physiological pH of around $7.4$ and human body temperature of ${37^ \circ }\,C$ under one atmospheric pressure. Under these conditions, most of the chemical reactions do not occur at appreciable rates if ordinary laboratory catalysts are used.

The activity of certain enzymes is increased in the presence of certain substances, called co-enzymes. It has been observed that if a protein contains small amount of vitamin as the non-protein part, its activity is enhanced considerably. The activators are generally metal ions such as $N{a^ + }$, $M{n^{2 + }}$, $C{u^{2 + }}$, $C{o^{2 + }}$ etc. These metal ions are weakly bonded to the enzyme molecules and increase their catalytic activity.

Just as in the case of catalysts, the activity of enzymes is slowed down in the presence of certain substances. Such substances are called inhibitors or poisons. They act by combining with the active functional group thereby reducing or completely destroying the catalytic activity of the enzymes. The use of many drugs is on account of their action as enzyme inhibitors in our body.