Solved Exercise, Bio-11, Ch-03


(i) Enzymes are composed of hundreds of _________. (amino acids)

(ii) Some enzymes consist of a non-protein part known as a _________. (co-factor)

(iii) Many enzymes require non-protein component called _________ for their proper functioning. (co-factor)

(iv) Enzymes are highly _________ in nature. (specific)

(v) The enzymes which carry out the synthesis of _________ are integral parts of ribosomes. (proteins)


(i) The enzymes important in photosynthesis are found in the mitochondria. (FALSE)

CORRECT: The enzymes important in photosynthesis are found in the chloroplasts.

(ii) Large amounts of an enzyme can accelerate chemical reactions. (FALSE)

CORRECT: Small amounts of an enzyme can accelerate chemical reactions.

(iii) Calvin Malvin proposed Lock and Key model for enzyme action. (FALSE)

CORRECT: Emil Fischer proposed Lock and Key model for enzyme action.

(iv) The active site of an enzyme is composed of four regions. (FALSE)

CORRECT: The active site of an enzyme is composed of two regions.

(v) Structure of an enzyme has no specific importance. (FALSE)

CORRECT: Structure of an enzyme has specific importance.


(i) If more substrate to an already occurring enzymatic reaction is added, more enzyme activity is seen because:              

(a)   There is probably more substrate present than there is enzyme.

(b)  There is probably more enzyme available than there is substrate.

(c)   There is probably more product present than there is either substrate or enzyme.

(d)  The enzyme substrate complex is probably failing to form during the reaction.

EXPLANATION: When there is more enzyme present than there is substrate, it means many empty active sites are available for the new substrate molecules. So, if substrate concentration is increased, these active sites are utilized and the reaction speeds up.

(ii) If you add more substrate to already occurring enzymatic reaction and it has no effect on the rate of reaction. What is the form given for this situation?

(a)   Saturation                                         

(b)  Denaturation

(c)   Composition                                     

(d)   Inhibition

EXPLANATION: It means all the active sites of enzymes are already saturated with the substrate molecules, and there are no more active sites available for the added substrate molecules to attach to and show increase in the rate of reaction.

(iii) The rate of an enzyme catalyzed reaction:

(a)   Is constant under all conditions.

(b)  Decreases as substrate concentration increases.

(c)   Can not be measured.

(d)  Can be reduced by inhibitors.

EXPLANATION: Inhibitors are those substances (drugs, antibiotics, poisons etc.) which reduce or retard the enzymatic activity, either by occupying the active sites or destroying the globular structure of enzyme other than active site.

(iv) The active site of an enzyme:

(a)   Never changes

(b)  Forms no chemical bond with substrate

(c)   Determines, by its structure, the specificity of the enzyme

(d)  Looks like a lump projecting from the surface of the enzyme

EXPLANATION: The active site, especially the binding site has a specific sequence and arrangement of amino acids. Due to this specific structure, the enzyme can attach only specific substrates to its binding site. So, the specific structure of the enzyme determines the specificity of the enzyme.

(v) Which statement about enzyme is not true?

(a)   They consist of proteins, with or without a non-protein part.

(b)  They change the rate of catalyzed reaction.

(c)   They are sensitive to heat.

(d)  They are non-specific in their action.

EXPLANATION: Enzymes are specific in their action because they have specific structures especially at binding sites, they have specific arrangement of amino acids which can bind only to a specific substrate molecule.


Two conditions that destroy enzymatic activity by disrupting bonds between the atoms in enzyme are:

(1) Very High temperature

(2) Extreme changes in pH

Effect of Low Temperature: At low temperatures, the rate of enzymatic reaction is decreased.

Effect of High Temperature: At high temperature, the rate of enzyme-controlled reaction will increase but upto a certain limit. This can be explained as:

(1) Heat supplies kinetic energy to the reacting molecules, and causes them to move rapidly. More molecules, now, cross the activation energy barrier. They make greater number of effective collisions and the rate of reaction is increased.

(2) However, further increase in heat energy also increases the vibrations of atoms which make up the enzyme molecule. If the vibrations become too violent, globular structure essential for enzyme activity is lost and the enzyme is said to be denatured. Thus, very high temperatures cause the denaturation of enzyme.

Prosthetic Group: “When the non-protein part of the enzyme is covalently bonded to the protein part, it is called prosthetic group.”

Examples: FAD or Flavin adenine dinucleotide, etc.

Enzyme Inhibitors: “An inhibitor is a chemical substance which can react (in place of substrate) with the enzyme but is not transformed into product(s) and thus blocks the active site temporarily or permanently.” 

Examples: Poisons like cyanide. Antibiotics, anti-metabolites and some drugs.

Types of Inhibitors: Inhibitors can be divided into two types: (i) Irreversible (ii) Reversible.

Enzyme lowers the activation energy of the reaction by changing its mechanism. Thus, it accelerates the metabolic reaction.


Please consult textbook at page 38 — 40.

Please consult textbook at page 41 — 42.

Please consult textbook at page 43.

Enzymes are the most important group of proteins which are biologically active. They tremendously increase the efficiency of a biochemical reaction and are specific for each type of reaction. Without these enzymes the reaction would proceed at a very slow speed making life impossible.

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