Chapter #6 bise Rawalpindi biology notes Enzymes short questions and Mcqs.
20 + MCQs On Enzymes Pdf
i) What is TRUE about enzymes?
- A. They make biochemical reactions proceed spontaneously
- B. They lower the activation energy of a reaction
- C. They are not very specific in their choice of substrates
- D. They are needed in large quantities
ii) To what category of molecules do enzymes belong?
- A. Carbohydrates
- B. Lipids
- C. Nucleic acids
- D. Proteins
iii) What is TRUE about cofactors?
- A. Break hydrogen bonds in proteins
- B. Help facilitate enzyme activity
- C. Increase activation energy
- D. Are composed of proteins
iv) Prosthetic groups are;
- A. Required by all enzymes
- B. Loosely attached with enzymes
- C. Proteins in nature
- D. Tightly bound to an enzyme
v) When we add more substrate to an already occurring enzymatic reaction and there is no increase in the rate of reaction, what would you predict?
- A. All active sites have been occupied by substrate molecules
- B. The enzyme molecules have denatured
- C. More substrate acted as an inhibitor
- D. More substrate has disturbed the pH of the medium
6. The general mechanism is that an enzyme acts by:
- Reducing the activation energy
- Increasing activation energy
- Decreasing pH value
- Increasing the pH value
7. The coenzyme is:
- Often a metal
- always a protein
- often a vitamin
- always an inorganic compound
8. An enzyme that joins the ends of two strands of nucleic acid is:
- Polymerase
- ligase
- synthetase
- Helicase
9. Which of the following is produced with the combination of apoenzyme and coenzyme:
- Holoenzyme
- Enzyme substrate complex
- Prosthetic group
- Enzyme product complex
10. Which one among them is the example of competitive inhibition of an enzyme:
- Succinic dehydrogenase by malonic acid
- Cytochrome oxidase by cyanide
- Hexokinase by glucose-6-phosphate
- Carbonic anhydrase by carbon dioxide
11. Diastase takes part in digestion of which one:
- Protein
- Starch
- Amino acids
- Fat
12. Enzyme complex involved in alcoholic fermentation is:
- Zymase
- Invertase
- Lipase
- Amylase
13. Zymogen or proenzyme is a :
- Modulator
- Vitamin
- Enzyme precursor
- Hormone
14. The nature of an enzyme is
(a) Lipid
(b) Vitamin
(c) Carbohydrate
(d) Protein
15. In alcoholism, this enzyme is elevated
(a) acid phosphatase
(b) hepatitis
(c) serum glutamate pyruvate transaminase
(d) glutamyl transpeptidase
16. With regards to enzyme action, this statement is incorrect
(a) Malonate is a competitive inhibitor of succinic dehydrogenase
(b) the substrate binds with the enzyme at its active site
(c) the non-competitive inhibitor binds the enzyme at a site distinct from that binding the substrate
(d) addition of a lot of succinates does not reverse the inhibition of succinic dehydrogenase by malonate
17. What is the count of genes that determine the synthesis of one enzyme?
(a) One
(b) Four
(c) Eight
(d) Sixteen
18. This enzyme was first isolated and purified in the form of crystals
(a) Urease
(b) pepsin
(c) Amylase
(d) Ribonuclease
19. Macromolecule chitin is
(a) a simple polysaccharide
(b) sulfur-containing polysaccharide
(c) phosphorous-containing polysaccharide
(d) nitrogen-containing polysaccharide
20. Enzyme-driven metabolic pathways can be made more efficient by
(a) grouping enzymes into multienzyme free-floating complexes
(b) concentrating enzymes with specific cellular compartments
(c) fixing enzymes into membranes so they are adjacent to each other
(d) all of these
21. Tryptophan synthetase of E.coli, a typical bifunctional oligomeric enzyme consists of
(a) a protein A and one subunit A
(b) a protein designated A
(c) two proteins designated A and B
(d) a protein designated B
22. This statement about enzymes is true
(a) enzymes accelerate reactions by lowering the activation energy
(b) enzymes are proteins whose three-dimensional form is key to their function
(c) enzymes do not alter the overall change in free energy for a reaction
(d) all of these
23. The enzyme COX-1 is vital for human health in this way:
(a) it is a chemical derivative of aspirin
(b) catalyzes the hormone production which maintains the stomach lining
(c) critical for the biosynthesis of DNA
(d) helps in the transportation of carbon dioxide in the blood
Read more:Cell Cycle bio G9 Notes bise Rawalpindi
Q.1) Define cofactor and coenzyme.
Answer:
Cofactor:
“A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme’s activity”.
Example:
Cofactors can be either inorganic (e.g. metal ions) or organic (e.g. flavin and heme).
Coenzyme:
“The organic cofactors of enzymes that are loosely attached with enzyme transport chemical groups from one enzyme to another”.
Example:
Some important vitamins (e.g. riboflavin, thiamine, and folic acid) act as coenzymes.
Q.2) What is the main use of enzymes in the paper industry?
Answer:
Use of enzymes in the paper industry:
Enzymes degrade starch to lower its viscosity which aids in making paper.
List the uses of enzymes in different industries.
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 which aids in making paper.
4) Biological detergents:
Protease enzymes are used for the removal of protein stains from cloths. Amylase enzymes are used in dishwashing to remove resistant starch residues.
Understanding The Concepts
Q.1) How would you define enzymes? Describe their characteristics.
Enzymes:
“Enzymes are proteins that catalyze i.e. speed up the biochemical reactions and are not changed during the reaction”.
The molecules at which enzymes act are called substrates, and the enzyme converts them into different molecules called products.
Characteristics of Enzymes
Characteristics of enzymes are as follows:
- Almost all enzymes are proteins i.e. they are made of amino acids.
- Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze.
- Enzymes are usually very specific for the type of reaction and for the nature of their substrates.
- Only a small portion of enzyme molecules is directly involved in catalysis. This catalytic region is known as the active site. It recognizes and binds the substrate and then carries out the reaction.
- Enzyme production can be enhanced or diminished by a cell according to needs. Enzyme activity can also be regulated by inhibitors and activators.
- Some enzymes do not need any additional components to work. However, others require non-protein molecules or ions called cofactors. Cofactors can be either inorganic (e.g. metal ions) or organic (e.g. flavin and heme). If organic cofactors are tightly bound to enzymes, they are called prosthetic groups. If organic cofactors are loosely attached to enzymes, they are called coenzymes. Coenzymes transport chemical groups from one enzyme to another. Some important vitamins (e.g. riboflavin, thiamine, and folic acid) act as coenzymes.
- Several enzymes work together in a specific order, creating metabolic pathways. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the reaction, the product is passed on to the next enzyme.
What do you mean by activation energy and why it is referred to in the definition of enzymes?
Enzymes are proteins that catalyze (i.e. speed up) biochemical reactions and are not changed during the reaction. The molecules at which enzymes act are called substrates, and the enzyme converts them into different molecules, called products.
All chemical reactions require activation energy. lt is defined as;
“The minimum energy required to start a reaction”.
The need for activation energy acts as a barrier to the beginning of the reaction. Enzymes lower such barriers by decreasing the requirement of activation energy. Thus, in the presence of enzymes, reactions proceed at a faster rate.
Ways by which enzymes lower the activation energy:
Enzymes lower the activation energy in several ways;
- They may alter the shape of the substrate and reduce the requirement of energy for this change.
- Some enzymes do so by disrupting the charge distribution on substrates.
- Enzymes may also lower activation energy by bringing substrates in the correct orientation to react.
In a range of 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:
An increase in temperature will speed up the rate of enzyme-catalyzed reactions, but only to a certain limit.
Above 35oC and below 0oC:
When the temperature is raised well above 35oC, the enzyme activity slows down and eventually stops because the heat energy increases the vibrations of atoms of enzyme molecules and the globular structure of the enzyme is lost. This is known as the denaturation of enzymes. It results in a rapid decrease in the rate of enzyme action and it can get blocked completely as well.
If the temperature lowers below 350C, the enzyme activity lowers until the enzyme reaches a minimum temperature at which the enzyme activity is the least. The enzyme activity stops completely at 0oC. The vibrations of atoms of enzyme molecules decrease, protein changes shape and the active site is no longer complementary to the substrate molecule.
How does pH affect enzyme activity?
pH affects enzyme activity:
All enzymes work at their maximum rate at a narrow range of pH, called optimum pH. A slight change (increase or decrease) in this pH causes retardation in enzyme activity or blocks it completely. Every enzyme has its specific optimum pH value.
Example:
Pepsin (an enzyme that works in the stomach) is active in an acidic medium (low pH) while trypsin (working in the small intestine) shows its activity in an alkaline medium (high pH). Changes in pH can affect the ionization of amino acids at the active site.
Q.5) What characteristic of enzymes makes them specific for substrates?
Answer:
Specificity of enzymes:
There are over 2000 known enzymes, each of which is involved in one specific chemical reaction. Enzymes are also substrate-specific.
Example:
The enzyme protease (which breaks peptide bonds in proteins) will not work on starch (which is broken down by an enzyme amylase). Similarly, the lipase enzyme acts only on lipids and digests them into fatty acids and glycerol.
Specificity is determined by the shape of the active site:
The specificity of different enzymes is determined by the shapes of their active sites. Active sites possess specific geometric shapes that fit with specific substrates.
Q.6) Briefly describe the factors that affect the activity of enzymes.
Answer:
Factors affecting enzyme activity:
Enzymes are very sensitive to the environment in which they work. Any factor that can change the chemistry or shape of the enzyme molecule, can affect its activity. Some of these factors that can affect the rate of enzyme action are:
1) Temperature
2) Substrate concentration
3) pH
1) Temperature:
An increase in temperature speeds up the rate of enzyme-catalyzed reactions, but only to a point. Every enzyme works at its maximum rate at a specific temperature called “the optimum temperature” for that enzyme.
When the temperature rises to a certain limit, the heat adds in the activation energy and also provides kinetic energy for the reaction. So reactions are accelerated. But when the temperature is raised well above the optimum temperature, heat energy increases the vibrations of atoms of the enzyme and the globular structure of the enzyme is lost. This is known as the denaturation of the enzyme. It results in a rapid decrease in the rate of enzyme action and it may be blocked completely.
2) Substrate concentration:
If enzyme molecules are available in a reaction, an increase in substrate concentration increases the rate of reaction. If enzyme concentration is kept constant and the amount of substrate is increased, a point is reached where any further increase in substrate does not increase the rate of reaction anymore. 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 the reaction rate does not increase.
3) pH:
All enzymes work at their maximum rate at a narrow range of pH, called optimum pH. A slight change (increase or decrease) in this pH causes retardation in enzyme activity or blocks it completely. Every enzyme has its specific optimum pH value.
Example:
Pepsin (an enzyme that works in the stomach) is active in an acidic medium (low pH) while trypsin (working in the small intestine) shows its activity in an alkaline medium (high pH). Changes in pH can affect the ionization of amino acids at the active site.
Bise Rawalpindi Bio 9th Cell and Tissue Cha 4
Q.7) Describe the lock and key mechanism of enzyme action.
Answer:
Lock and key mechanism of enzyme action:
In order to explain the mechanism of enzyme action a German chemist Emil Fischer, in 1894, proposed the lock and key model. According to this model, both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another. This model explains enzyme specificity.
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