Enzymes - Home of Knowledge


Enzymes and Enzymology


Question#1) Write a short note on enzyme?

Answer: Enzyme: Enzymes are proteins that catalyze (speed up) biochemical reactions by lowering its activation energy and are not changed during the reaction.

All enzymes are catalysts but all catalysts are not enzymes. Only biocatalysts are called enzymes. Word enzyme was first used by a German physiologist kuhne in 1878.

Word study: Word enzyme means ferment or yeast.

The study of enzymes is called Enzymology or Zymology.

Other names: Biocatalysts, Biotransformation.

Known enzymes: At present, there are about 4,000 kinds of enzymes whose actions are well known.

Question#2) Define metabolism and its types?

Answer: Metabolism (metabolism means change): Metabolism is the set of biochemical reactions that occur in living organisms in order to maintain life. Concept of metabolism was first proposed by Ibn-E-Nafees, who stated that “the body and its parts are always undergoing change”.

Types of metabolism: there are two types of metabolism.

1) Anabolism: Anabolism includes the biochemical reactions in which larger molecules are synthesized.

Energy is utilized in anabolism by the formation of bonds.

Example: Amino acids combined to form proteins.

2) Catabolism: Catabolism includes the biochemical reactions in which larger molecules are broken down.  

Energy is released in catabolism by the breakdown of bonds.

Example: decomposition of proteins into amino acids.

Question#3) Define the following?

  • Substrate
  • Products
  • Activation energy.
  • Apoenzyme
  • Holoenzyme

Answer: 1) Substrate: The molecules at which enzymes act are called substrates.

2) Products: The substances formed after completion of an enzymatic reaction are called products.

3) Activation energy: The minimum energy required to start a reaction is called activation energy.

4) Apoenzyme: The protein part of an enzyme without cofactor is called apoenzyme.

5)  Holoenzyme: The apoenzyme along with cofactor attach to it is called holoenzyme or complete enzyme.


Question#4) How enzymes lower the activation energy?

Answer: Enzymes lower the activation energy in several ways.

1) They may alter the shape of substrate and reduce the requirement of energy for this change.

2) Some enzymes do so by disrupting the charge distribution on substrates.

3) Enzymes may also lower activation energy by bringing substrates in the correct orientation to react.

Types of Enzymes: Enzymes can be categorized on the basis of the site where they work.

Enzymes can be categorized on the basis of the site where they work i.e. they may be

1) Intracellular enzymes: Enzymes that perform functions inside the cells are called intracellular enzymes. (E.g. enzymes of glycolysis work in the cytoplasm).

2) Extracellular enzymes: Enzymes that perform functions outside the cells are called Extracellular enzymes. (E.g. pepsin enzyme working in the stomach cavity).


Question#5) Write the characteristics of enzymes?

Answer: CHARACTERISTICS OF ENZYMES: important characteristics of enzymes are as follows.

1) Shape and size: These are globular proteins made of long linear chain of amino acids that fold to produce three dimensional molecule.  Most enzymes are larger than the substrates on which they act.

2) Chemical composition: • Almost all enzymes are proteins i.e. they are made of amino acids. Sometime RNA also functions as enzyme. When RNA functions in this capacity, it is called Ribozyme.

3) Rate of Reaction: • Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions.

4) In-consumable: As with all catalysts, enzymes are not consumed by the reactions they catalyze.

5) Enzyme specificity: • Enzymes are usually very specific for the type of reaction and for the nature of their substrates.

6)Active sites of enzymes:  • Only a small portion of enzyme molecule is directly involved in catalysis. This catalytic region is known as active site It recognizes and binds substrate and then carries out reaction.

7) Enzymes regulation:  Enzyme production can be enhanced or diminished by a cell according to needs. Enzyme activity can also be regulated by inhibitors and activators.

8) Cofactor:  The non-protein substances that bind with enzymes and enhance their actions are called cofactors.

“OR”     any of various organic or inorganic substances necessary to the function of an enzyme.

Prosthetic groups : Prosthetic groups are cofactors that bind tightly to proteins or enzymes. They can be organic or metal ions and are often attached to proteins by a covalent bond. E.g, zinc, copper,iron,

Coenzymes: Organic cofactors that are loosely attached with enzymes are called coenzymes. E.g, vitamins (riboflavin, thiamine and folic acid)

9)Metabolic pathways: Several enzymes can work together in a specific order, creating metabolic pathways, In which one enzyme takes the product of another enzyme as a substrate. After the reaction, the product is passed on to the next enzyme.

10) Small amount: only small amount of enzymes are needed for a reaction,

11) Intracellular and extracellular enzymes: some enzymes are found inside cells and are called intracellular enzymes. E.g, nuclease.

Extracellular enzymes: Enzymes that are released so that, they have their effects outside the cells are called extracellular enzymes.   

Question#6)  What are the major uses of enzymes? Also describe the factors that affect enzymes activities?

Answer: Uses of enzymes: Enzymes are extensively used in different industries for fast chemical reactions. For example;

  1. Food industry: Enzymes that break starch into simple sugars are used in the production of white bread, buns etc.
  2. Brewing industry: Enzymes break starch and proteins. The products are used by yeast for fermentation (to produce alcohol).
  3. Paper industry: Enzymes break starch to lower its viscosity that aids in making paper.
  4. Biological detergent:Protease enzymes are used for the removal of protein stains from clothes. Amylase enzymes are used in dish washing to remove resistant starch residues.


Enzymes are very sensitive to the environment in which they work. Any factor that can change the chemistry or shape of enzyme molecule, can affect its activity. Some of the factors that can affect the rate of enzyme action are discussed as follows.

1) Temperature: Each and every enzyme works well at a specific range of temperature called optimum temperature.  Increase in temperature generally increase enzyme activity but only to a point. Too much increase in temperature change three dimensional structure of enzymes. Thus enzymes denature and there functions are disturbed. Optimum temperature for human enzymes is 37cº. Very low temperature also reduces enzyme activity.

2)  substrate concentration: If enzyme molecules are available in a reaction, increase in substrate concentration increases the rate of reaction. If enzyme concentration is kept constant and amount of substrate is increased, a point is reached where any further increase in substrate does not increase the rate of reaction any more. When the active sites of all enzymes are occupied (at high substrate concentration), any more substrate molecules do not find free active sites. This state is called saturation of active sites and reaction rate does not increase and the enzyme is called saturated enzyme.

3) pH

All enzymes work at their maximum rate at a narrow range of pH, called as the optimum pH. Optimum PH for most of human enzyme is 6-8. A slight change in this pH causes retardation in enzyme activity or blocks it completely. Every enzyme has its specific optimum pH value. For example pepsin (working in stomach) is active in acidic medium (low pH of 2) while trypsin (working in small intestine) shows its activity in alkaline medium (high pH of 8). Change in pH can affect the ionization of the amino acids at the active site.

Question#7) How enzyme substrate complex is formed?


When enzyme attaches with substrate, a temporary enzyme-substrate (ES) complex is formed. Enzyme catalyzes the reaction and substrate is transformed into product. After it, the ES complex breaks and enzyme and product are released.

Enzyme + Substrate → Enzyme Substrate complex → Enzyme + Products.

E+S → ES complex → E+P

Question#8) Describe the lock and key model of enzyme action?

Answer: In order to explain the mechanism of enzyme action a German chemist Emil Fischer, in 1894, proposed lock and key model. According to this model, both enzyme and substrate possess specific shapes that fit exactly into one another. This model explains enzyme specificity.

Question#9) write a short note on induced fit model?

Answer: Induced fit model or induced fit hypothesis:

In 1958, an American biologist Daniel Koshland suggested a modification to lock and key model and proposed induced-fit model. According to this model, active site is not a rigid structure rather it is molded into the required shape to perform its function. Induced fit model is more acceptable than “lock and key” model of enzyme action..

Question#10) Describe specificity of enzymes?


There are over 2000 known enzymes, each of which is involved in one specific chemical reaction. Enzymes are also substrate specific. The enzyme protease (which breaks peptide bonds in proteins) will not work on starch (which is broken down by an enzyme amylase . Similarly lipase enzyme acts only on lipids and digests them into fatty acids and glycerol. Specificity of different enzymes is determined by the shapes of their active sites. Active sites possess specific geometric shapes that fit with specific substrates.

Question#11) In a range of temperature from   0-35°C, the rate of reaction of an enzyme is proportional to temperature. Above 35°C and below 0°C, enzyme activity slows down and eventually stops.Explain why?

Answer: Relationship between enzyme action and functions of enzymes: Each and every enzyme works well at a specific range of temperature called optimum temperature.  Increase in temperature generally increase enzyme activity but only to a point.  In a range of temperature from   0-35°C, the rate of reaction of an enzyme is proportional to temperature. Too much increase in temperature change three dimensional structure of enzymes. Thus enzymes denature above 35 Ċ and there functions are disturbed.  Below 0 Ċ the enzymes condenses and  its functions slows down or fully stopped. Optimum temperature for human enzymes is 37cº.

Question#12) What characteristic of enzymes makes them specific for substrates?

Answer: Active site of an enzyme and chemical composition of enzymes makes them specific for  substrates. The portion of enzyme to which the substrate attaches is called active site. Active site has a specific chemical composition and shape. That’s why specific substrate are attaches to them. And in this it makes enzyme specific for action.

Question#13) What do you mean by activation energy and why it is referred in the definition of enzymes?

Answer: Activation energy: Activation energy is the minimum energy required to start a reaction. Enzymes lower the activation energy. This is how it is referred in the definition of  enzymes. Without enzymes the biochemical reactions are unable to proceed because of high activation energy. In the presence of enzymes the activation energy decreases and hence the biochemical reactions proceed at a very faster rate. So there establishes a relationship between enzymes and activation energy. So activation energy is referred  in the definition of  enzyme.

Question#14) What is the main use of enzymes in paper industry?

Answer: Enzymes break starch to lower its viscosity that aids in making paper.

Question#15) Define the following terms.

Answer: Lipase: Enzymes  that break down lipids are called lipase. Amylase: Enzymes that act on starch are called amylase.

Protease: Enzymes that act on proteins are called protease.

Denaturation: The process of modifying the molecular structure of a protein is called denaturation. Denaturation involves the breaking of many of the weak linkages, or bonds (e.g., hydrogen bonds), within a protein molecule that are responsible for the highly ordered structure of the protein in its natural (native) state. Denatured proteins have a looser, more random structure; most are insoluble. Denaturation can be brought about in various ways—e.g., by heating, by treatment with alkali, acid, urea, or detergents, and by vigorous shaking.

Optimum pH : The narrow range of  PH at which enzymes works at  their maximum rate is called as the optimum pH.

Product s: The species (substances) that are formed after completion of  a chemical reaction are called products.  

Optimum temperature: The temperature at which enzymes works at their maximum rate is called as the optimum temperature. 

Enzyme-substrate  complex:  When an enzyme combined to its substrate an enzyme substrate complex is formed. 

Catalyst: A substance able to increase the rate of a chemical reaction without itself being consumed or changed by the reacting chemicals is called a catalyst.

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