Enzymes Chapter 3 Easy Notes and Solved Mcqs with Past NMDCAT Questions
CHAPTER # 03
ENZYMES
ENZYMES: Chemical substances which work in chemical reactions and speed up the reaction are called enzymes. They are also called biocatalysts and were found and named by Friedrich Wilhelm Khune (1878)
RIBOENZYMES: When ribonucleic acid works as an enzyme, it is termed as ribo-enzyme.
INTRACELLULAR ENZYME: An enzyme that reacts with a substrate in a cell in which the enzyme was produced is called an intracellular enzyme or endo-enzyme. E.g. Pepsin is produced in the stomach and it digests protein in the stomach.
EXTRACELLULAR ENZYME: An enzyme that is produced in one cell and works somewhere else is called an extracellular enzyme. E.g. Carbohydrase is an enzyme. It is produced in the pancreas and digests disaccharide carbohydrates in the small intestine. Extracellular enzymes are also called exo-enzymes.
ACTIVE SITE: An area in the molecule of an enzyme where a substrates molecule enters so that enzyme may act on it.
LOCK AND KEY MODEL: A model introduced by Fischer (1898). According to this model, the shape of the molecule must be the same as the shape of the active site of an enzyme. If a shape is different, the enzyme will not act on a substrate.
INDUCED FIT MODEL: A model introduced by Koshland (1959). According to this model, it is not necessary that the active site and substrate molecule should have the same shape. A substrate molecule with a different shape may induce inside the active site of the enzyme and change its shape. Finally, the enzyme will act on the substrate.
HOLOENZYME: A conjugated enzyme that is totally active is called holo-enzyme. This explanation was given by Euler (1932).
APOENZYME: The protein part of the enzyme is called apo-enzyme
PROSTHETIC GROUP: The non-protein part of the enzyme is called the prosthetic group.
OXIDASES ENZYME: A type of enzyme which oxidizes the substrate. E.g. Oxido-reductases and dehydrogenizes.
TRANSFERASES: An enzyme that transfers carbon group from one substrate to another substrate.
HYDROLASES: An enzyme that cleavages (breaks up) a single bond between molecules of a substrate by adding a molecule of water. E.g. glycosidases, phosphates, etc.
LYASES: An enzyme that cleavages substrate without adding water. E.g. aldolases, dehydratases
ISOMERASES: An enzyme that changes the structure of a substrate without changing its atomic composition.
LIGASES: An enzyme that combines atoms to synthesize a new molecule. This enzyme is used in making ATP by adding one phosphate to ADP.
COFACTOR: If the non-protein part of an enzyme is made up of inorganic, it is called a cofactor.
COENZYME: If the non-protein part of the enzyme is organic in nature, it is called a coenzyme.
ACTIVATOR: A chemical that further increases the rate of enzymatic action is called an activator. E.g. Mg
INHIBITOR: A chemical that can reduce the rate of enzyme or even may stop the enzyme from working.
COMPETITIVE INHIBITOR: When an inhibitor blocks the active site of the enzyme and does not allow the substrate to attach to the enzyme, it is called a competitive inhibitor.
NON-COMPETITIVE INHIBITOR: A type of inhibitor which comes from the opposite side of the active site and changes its shape is called a non-competitive inhibitor.
ALLOSTEIC SITE: The opposite site of the active site is called an allosteric site.
FEEDBACK INHIBITION: A kind of inhibitory mechanism, in which the product gives feedback to the enzyme, and the enzyme, stops its activity. This happens when the product is abundant.
MCQ’s
1. The biocatalysts are synthesized inside the cells and are also called
(a) Allozymes (b) Enzymes
(c) Co-enzymes (d) All
2. Friedrich Wilhelm Khune coined the word enzymes in
(a) 1878 (b) 1879
(c) 1875 (d) None
3. a statement that organic substances capable of catalyzing specific chemical reactions in living system fit on
(a) Proteins (b) Carbohydrates
(c) Enzymes (d) None
4. Thomas Chech and Sidney Altman discovered that one of the following molecules also function as enzymes
(a) Ribonueclic acid (b) Deoxyribonucleid
(c) Both (d) None
5. Generally enzymes are ---------in nature
(a) Non-pretentious (b) Protenious
(c) Activators (d) Inhibitors
6. The enzymes -----------the the activation energy of reaction
(a) Lower down (b) Do not play any role
(c) Speed up (d) None
7. If an enzyme acts in the same cell, where it is synthesized, it will be known as
(a) Inter-cellular (b) Intracellular
(c) Extra-cellular (d) None
8. One of the following has the same meaning as intracellular enzyme
(a) Exo-enzyme (b) Endo-enzyme
(c) Both a&b (d) None
9. One of the following enzymes is entirely made up of proteins
(a)Amylase (b) Pepsin
(c) Both a&b (d) None
10. Enzymes are specific in their nature and action
(a) True (b) False
11. The action of enzymes may be further enhanced by adding
(a) Activators (b) Inhibitors
(c) Both a&b (d) None
12. One in all following is activators
(a) Mn (b) Ni
(c) K (d) Zn
13. The size of enzyme molecule is -------then the size of the substrate
(a) Smaller (b) Equal
(c) Larger (d) None
14. The enzymes remain unchanged during and after the chemical reaction
(a) True (b) False
15. The area of the enzyme into which the substrate fits for a chemical reaction is called
(a) Reaction area (b) Passive area
(c) Active site (d) All
16. The Key and Lock model was proposed by
(a) Kinley in 1798 (b) Fischer in 1898
(c) Lamark in 1899 (d) None
17. Enzyme can react with the substrate. This theory was modified by Paul Filder and
(a) G.G. Weed (b) D.D. Woods
(c) H.G. Wells (d) None
18. The induced fit model was proposed by
(a) Koshland-1959 (b) D.D. Woods 1959
(c) H.G. Wells 1959 (d) None
19. When a substrate combines with an enzyme, it induces changes in the enzyme structure to enable the enzyme to perform an activity. This explains --------------model
(a) Lock and Key (b) Induced Fit
(c) Both (d) None
20. Enzymes that are only made up of proteins are called
(a) Conjugated (b) Simple
(c) Allonyms (d) None
21. Holoenzymes refer to
(a) Conjugated enzymes (b) Simple enzymes
(c) Both (d) None
22. An enzyme may be made up of protein and non-protein parts. Its protein part is called
(a) Apoenzyme (b) Prosthetic group
(c) Both (d) None
23. An enzyme may be made up of protein and non-protein parts. Its non-protein part is called
(a) Apoenzyme (b) Prosthetic group
(c) Both (d) None
24. A Holoenzymes in which prosthetic group is in-organic ions are called
(a) Co-factors (b) Co-enzymes
(c) Both a&b (d) None
25. A Holoenzymes in which prosthetic group is organic ions are called
(a) Co-factors (b) Co-enzymes
(c) Both a&b (d) None
26. A co-enzyme constitutes about --------percent of the entire enzyme molecule
(a) 4 (b) 3
(c) 2 (d) 1
27. One of the following is an example of co-enzyme
(a) NAD (b) FAD
(c) Both a&b (d) None
28. The presence of enzymes speed up the reaction and lower the energy utilization
(a) True (b) False
29. The substance that an enzyme acts upon is known as
(a) Product (b) Substrate
(c) Active site (d) None
30. Enzymes are also known as
(a) Bio-catalysts (b) Catalysts
(c) Both a&b (d) None
31. Enzymes work properly at the optimum temperature of –-----degree centigrade
(a) 37 (b) 38
(c) 39 (d) 40
32. Proteins become denatured and are destroyed at--------degree centigrade
(a) 90 (b) 100
(c) 80 (d) 85
33. Low temperature is relatively better than high temperature
(a) True (b) False
34. For pepsin, the optimum pH is
(a) 1.6 (b) 1.5
(c) 1.4 (d) None
35. Enzyme action is frequently accelerated or inhibited by the presence of other substances called
(a) Co-enzymes (b) Inhibitors
(c) Activators (d) Co-factors
36. When a co-factor is an organic molecule, it is called
(a) Co-enzyme (b) Co-factor
(c) Inhibitor (d) None
37. Inorganic substances which increase the activity of an enzyme are called
(a) Co-enzyme (b) Activators
(c) Inhibitor (d) None
38. One of the following is not an activator
(a) K (b) Na
(c) NAD (d) All
39. Magnesium is the activator for
(a) Phosphotase (b) Carbonic enhydrase
(c) Both a&b (d) None
40. Substances that decrease the activities of enzymes are called
(a) Co-factors (b) Inhibitors
(c) Co-enzymes (d) None
41. If an inhibitor resembles the substrate and compete for admission into the active site is called
(a) Non-competitive inhibitors (b) Competitive inhibitors
(c) Both a&b (d) None
42. When the inhibitor obstructs the enzymatic reaction by binding to a part of the enzyme away from the active site is called
(a) Non-competitive inhibitors (b) Competitive inhibitors
(c) Both a&b (d) None
43. In non-competitive inhibition, molecules that bind to an enzyme other than its active site is called
(a) Allosteric site (b) Prosthetic site
(c) Both a&b (d) None
44. Enzymes are------when they are exposed to ultraviolet light
(a) Activated (b) In-activated
(c) Inhibited (d) None
45. penicillin blocks the active site of the enzyme which helps the bacteria to make
(a) Cell membrane (b) Cell wall
(c) Ribosomes (d) None
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