Enzyme

Question 1

Extreme change in Ph causes:

Answer 1

Bonds in the enzymes to break

Question 2

amino acid

Answer 2

Typically, the active site is formed by 3 to 12 amino acids.

Question 3

Induce Fit Hypothesis

Answer 3

Koshland (1959) proposed this hypothesis/model

Question 4

Naming and Classifying Enzymes

Answer 4

International Union of Biochemistry has developed a scheme for naming and
classifying enzymes. Enzymes are mostly named by adding the suffix -ase to the
name of their substrate. The rest of the name indicates the nature of the reaction.
For example, alcohol dehydrogenase - catalyzes the removal of hydrogen from
alcohol (ethanol).

Question 5

Oxidoreductases

Answer 5

These are involved in oxidation and reduction (redox) reactions. In aerobic respiration, most of the cells ATP is generated by redox
reactions.

Question 6

Transferases:

Answer 6

These catalyze the transfer of a chemical group from one compound another. Transfer of an amino group from an amino acid to another
organic acid in the process of transamination.

Question 7

Hydrolases:

Answer 7

These catalyze hydrolyses (splitting by use of water) reactions. Most digestive enzymes are hydrolases.

Question 8

Lyases:

Answer 8

These catalyze the breakdown of molecules by reactions that do not involved hydrolysis.

Question 9

Isomerases:

Answer 9

These catalyze the transformation of one isomer into another, for instance the conversion of glucose 1,6 bisphosphate into fructose 1,6
bisphosphate.

Question 10

Ligases:

Answer 10

These form bonds between compounds using ATP. For example, DNA ligase is involved in the synthesis of DNA.

Question 11

Enzyme Inhibitors

Answer 11

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 (for example poisons, like cyanide, antibiotics,
antimetabolites and some drugs).
OR
Enzyme inhibitors are molecules that interact in some way with the enzyme to
prevent it from working in the normal manner.
Inhibitors may be nonspecific or specific. Specific inhibitors may be irreversible or
reversible. (Competitive and non-competitive)

Question 12

Non-specific Inhibitors

Answer 12

A non-sspecific inhibition affects all enzymes in the same way. Non-specific methods
of inhibition include any physical or chemical changes which ultimately denature the
protein portion of the enzyme.
Two main types are:
• Temperature
Usually, the reaction rate increases with temperature, but with enzyme reactions,
a point is reached when the reaction rate decreases with increasing temperature.
At high temperatures the protein part of the enzyme begins to denature, thus
inhibiting the reaction.
• Acids and Bases
Enzyme activity is also controlled by pH. As the pH is decreased or increased the
nature of the various acid and amine groups on side chains is altered with
resulting changes in the shape or structure of the enzyme.

Question 13

Specific Inhibitors

Answer 13

Specific inhibitors may be irreversible or reversible (competitive and
noncompetitive).
Irreversible Inhibitors
• These form strong covalent bonds with an enzyme.
• These inhibitors may act at near or remote from the active site.
• They may not be displaced by the addition of excess substrate.
• The basic structure of the enzyme is modified to the degree that it ceases to
work.
• Since many enzymes contain sulfhydral (– SH), alcohol, or acid groups as part
of their active sites, any chemical which can react with them acts as an
irreversible inhibitor. Heavy metals such as Ag+, Hg2+,Pb2+ have strong
affinities for –SH groups.
Reversible Inhibitors
They form weak linkages with the enzyme. Their effect can be neutralized
completely or partly by increase in the substrate concentration.
They are of two types which are competitive and non-competitive.

Question 14

Competitive Inhibitors

Answer 14

They have structural similarity with the substrate and are selected by the binding
sites cannot activate the catalytic sites. As a result product(s) are not formed.
(a) Formation of enzyme-substrate complex resulting in the formation of product.
(b) Inhibitor malonic acid does not fit the active site, hence no product is formed.

Question 15

Non-Competitive Inhibitors

Answer 15

They form enzyme inhibitor complex at a point other than the active site. They are
the enzyme structure in such a way that even if a substrate binds the active site
catalysis does not occur.

Question 16

cofactor

Answer 16

There are three kinds of a cofactor:
(a) The detachable inorganic ion (metal ion) working as co-factor is known
as an activator e.g. Cu/Zn.
(b) The covalently bonded non-protein part of enzymes is known as
prosthetic group e.g., Lipids.
(c) If the non- protein portion is loosely attached to the protein part it is
known as coenzyme e.g. Vitamins

Question 16

cofactor

Answer 16

There are three kinds of a cofactor:
(a) The detachable inorganic ion (metal ion) working as co-factor is known
as an activator e.g. Cu/Zn.
(b) The covalently bonded non-protein part of enzymes is known as
prosthetic group e.g., Lipids.
(c) If the non- protein portion is loosely attached to the protein part it is
known as coenzyme e.g. Vitamins

Question 17

Apoenzyme

Answer 17

An enzyme with its coenzyme or prosthetic group removed

Question 18

Holoenzyme.

Answer 18

An activated enzyme consisting of polypeptide chain and a cofactor.

Question 19

Many enzymes are dissolved in the cytoplasm.

Answer 19

Others are bound to the subcellular
organelles.
For example:
(a) Enzymes for photosynthesis are present in the Chloroplasts.
(b) Enzymes for cellular respiration are present in the Mitochondria.
(c) Some enzymes of protein synthesis are present in Ribosomes

Question 20

why pepsin is form in inactive form

Answer 20

Some enzymes are damaging if they become active in the wrong place. Pepsin
produced in inactive pepsinogen form. If it is produced in the active form .it
may cause cancer.

Question 21

mechainism of enzymes formation (catalysis)

Answer 21

The binding site helps in identification/Recognition and binding of a proper
substrate: form E-S complex. This reaction activates the catalytic site. The
catalytic site catalyzes the transformation of substrate into product(s). The
enzyme after catalysis detaches from the products unchanged.

Question 22

substrate concentration

Answer 22

If substrate concentration is unlimited then the rate of reaction depends on the amount of enzyme present at a specific time. If the amount of enzyme is doubled the reaction rate is also doubled.
Reason: The increase in enzyme number causes increase in active sites. More
active sites will convert more substrate into product(s), in a given time.
At low substrate concentration the reaction rate is directly proportional to the
substrate.
If the enzyme concentration is constant the rate of reaction increases with an
increase with substrate concentration.

Question 23

optimum
temperature

Answer 23

The temperature at which activity of enzyme is maximum is called as optimum
temperature. The increase in temperature causes increase in reaction rate of
enzyme up to a certain limit. For enzymes of human body 37°C is the optimum
temperature.
Heat provides activation energy. Heat also supplies kinetic energy to the
molecules. At high temperature globular structure is lost and the enzyme is
denatured. Globular structure is necessary for enzyme activity,

Question 24

optimum pH

Answer 24

The enzymes function at narrow pH range is called optimum pH. A slight
change in ‘pH can change the ionization of the amino acids at the active site and
the ionization of the substrates. Now enzyme activity is either retard or blocked
completely. A great change in pH causes the bonds in the enzyme to break. The
result is the denaturation of enzyme.

Question 25

Enzyme saturation

Answer 25

A condition in which all of the active sites of enzymes are occupied by substrate
molecules is called Enzyme saturation

Question 26

Enzyme-substrate (ES) complex

Answer 26

A complex consisting of an enzyme and its reactant (substrate) which is held
together by weak bonds is called Enzyme-substrate (ES) complex. The
formation of an ES is the first step in enzyme catalysis.

Question 27

Feedback inhibition.

Answer 27

A type of metabolic pathway control that regulates the rate at which the cells
synthesize amino acids (or other monomers) and use them in building proteins
(or other polymers) is called Feedback inhibition.

Question 28

Allosteric enzyme

Answer 28

Allosteric enzyme is an enzyme that undergoes reversible changes in shape and in catalytic activity.

Question 29

Imp points (1)

Answer 29

1. The catalytic activity of an enzyme is due to active site. It is a small portion of
   enzyme consisting of few amino acids.
2. The enzyme and its substrate react with each other through active sites.
3. The active site is a three dimensional cavity bearing a specific charge.
4. Most of the enzymes have a non-protein part known as a co-factor.
5. Cofactor is directly involved in chemical reaction for catalysis. Cofactor acts
   as “bridge” between enzyme and its substrate. Sometimes the co-factor
   provides energy to drive the reactions.
6. There are three kinds of a cofactor:
   (a) The detachable inorganic ion (metal ion) working as co-factor is known
   as an activator e.g. Cu/Zn.
   (b) The covalently bonded non-protein part of enzymes is known as
   prosthetic group e.g., Lipids.
   (c) If the non- protein portion is loosely attached to the protein part it is
   known as coenzyme e.g. Vitamins.
7. An enzyme with its coenzyme or prosthetic group removed is called Apoenzyme.
8. An activated enzyme consisting of polypeptide chain and a cofactor is known a, Holo enzyme.
9. The conditions under which enzymatic activity is destroyed by disrupting bonds between the atoms in an enzyme are: High temperature and extreme changes in pH.
10. Enzymes are also produced in the cells near the site of function.

Question 30

Imp point (2)

Answer 30

11. Many enzymes are dissolved in the cytoplasm. Others are bound to the sub-
    cellular organelles.
    For example:
    (a) Enzymes for photosynthesis are present in the Chloroplasts.
    (b) Enzymes for cellular respiration are present in the Mitochondria.
    (c) Some enzymes of protein synthesis are present in Ribosomes.
12. All metabolic activities occurring in the cells are carried out by specific
    enzymes.
13. Enzymes are sensitive to a small change in pH, temperature and substrate
    concentration.
14. Some enzymes are damaging if they become active in the wrong place. Pepsin
    produced in inactive pepsinogen form. If it is produced in the active form .it
    may cause cancer.
15. Mechanism of enzyme action is called catalysis.
16. The active site of the enzyme is made up of binding site and catalytic site.
17. The binding site helps in identification/Recognition and binding of a proper
    substrate: form E-S complex. This reaction activates the catalytic site. The
    catalytic site catalyzes the transformation of substrate into product(s). The
    enzyme after catalysis detaches from the products unchanged.
18. An enzyme has specific function because its chemistry and configuration
    (shape) is specific. Any factor that can change the chemistry and shape of an
    enzyme can affect its rate of catalysis.
19. Some factors that can affect the rate of enzyme action are: enzyme
    concentration, substrate concentration, temperature, and pH value.
20. If substrate concentration is unlimited then the rate of reaction depends on the
    amount of enzyme present at a specific time. If the amount of enzyme is
    doubled the reaction rate is also doubled

Question 31

Imp points (3)

Answer 31

21. Reason: The increase in enzyme number causes increase in active sites. More
    active sites will convert more substrate into product(s), in a given time.
22. At low substrate concentration the reaction rate is directly proportional to the
    substrate.
23. If the enzyme concentration is constant the rate of reaction increases with an
    increase with substrate concentration.
24. The temperature at which activity of enzyme is maximum is called as optimum
    temperature. The increase in temperature causes increase in reaction rate of
    enzyme up to a certain limit. For enzymes of human body 37°C is the optimum
    temperature.
25. Heat provides activation energy. Heat also supplies kinetic energy to the
    molecules. At high temperature globular structure is lost and the enzyme is
    denatured. Globular structure is necessary for enzyme activity,
26. The enzymes function at narrow pH range is called optimum pH. A slight
    change in ‘pH can change the ionization of the amino acids at the active site and
    the ionization of the substrates. Now enzyme activity is either retard or blocked
    completely. A great change in pH causes the bonds in the enzyme to break. The
    result is the denaturation of enzyme.
27. A condition in which all of the active sites of enzymes are occupied by substrate
    molecules is called Enzyme saturation.
28. A complex consisting of an enzyme and its reactant (substrate) which is held
    together by weak bonds is called Enzyme-substrate (ES) complex. The
    formation of an ES is the first step in enzyme catalysis.
29. A type of metabolic pathway control that regulates the rate at which the cells
    synthesize amino acids (or other monomers) and use them in building proteins
    (or other polymers) is called Feedback inhibition.
30. An organic molecule that functions as a coenzyme is the Vitamin.
31. Allosteric enzyme is an enzyme that undergoes reversible changes in shape and in catalytic activity.