Il. Multiple Choice Questions 1. Enzymes are a. proteins that always serve to in
ID: 280237 • Letter: I
Question
Il. Multiple Choice Questions 1. Enzymes are a. proteins that always serve to increase the activation energy needed for a reaction to take place b. proteins that serve as biological catalysts c. blological catalysts that always require a cofactor in order to function normally d catalysts that function equally well regardless of temperature or pH changes. e.biological catalysts that are only involved in catabolic reactions The site on an enzyme where the substrate binds is called the a site of activation. b. prosthetic group. c. substrate affinity site d. keyhole site. e. active site. 3. Enzymest a lower, increase b. lower, decrease c. raise; increase d. raise; decrease e. lower, do not affect the activation energy of a reaction and the rate of the reaction. 4. Metabolism is a. the total of all the exergonic reactions in an organism. b. the total of all the endergonic reactions in an organism. c the breakdown of sugars for energy in an organism. d the total of all chemical reactions that occur in an organism. e. the total of all reactions that require an input of energy in an organism. 5. In an enzyme-catalyzed reaction, a competitive inhibitor a. decreases the Km for the substrate b. does not change the Vmax for the reaction. c. lowers the Vmax for the reaction d. increases the apparent Km for the substrate. e. Both b and d are correct 6. In an enzyme-catalyzed reaction, the rate (velocity) of the reaction increases with increasing substrate concentration up to a certain point and then levels off at what is termed the Vmax. Why does the velocity level off instead of continuing to increase linearly with increasing substrate concentration? a. It levels off because the available cofactors run out b. It levels off because the reaction stops once equilibrium is reached. C. It levels off because the enzymes begin to wear out and break down. d. It levels off because all of the available enzymes are saturated and the reaction cannot go any faster without adding more enzymes e. It levels off because competitive inhibitors don't allow the reaction to go any faster 7. Why would a slight modification of an enzyme's tertiary structure potentially affect its function? a. A change in tertiary structure would be irrelevant to the function of an enzyme. b. The change in tertiary structure could alter the active site so that the binding affinity for the substrate was altered c. The change in tertiary structure could alter the active site so that induced fit is altered, causing a change in function d. A change in tertiary structure would only alter function of enzymes that are embedded in membranes. e. Both b and c are correctExplanation / Answer
Q.1
Answer: Option B.
Explanation: Enzymes decrease the activation energy needed for a reaction to take place. Most of the enzymes do require cofactor to become active, but there are some enzyme which does not require cofactor for catalytic reaction such as Dioxygenase. The catalytic activity of an enzyme varies with an increase or decrease in the temperature or pH. Enzymes are involved in both catabolic and anabolic reaction.
Q.2
Answer: Option E.
Explanation: Enzymes forms a temporary bond at active sites residue. It is the site for substrate binding. The residue which catalyse the reaction are found in the catalytic site.
Q.3
Answer: Option A.
Explanation: The energy required to start a reaction is known as activation energy. Enzymes are biological catalyst which decreases the activation energy of a reaction thereby increasing the rate of the reaction.
Q.4
Answer: Option D.
Explanation: Metabolism is the total of all chemical reaction that occur in an organism which includes both anabolic and catabolic reaction.
Q.5
Answer: Option E.
Explanation: Competitive inhibitor increases the apparent Km for the substrate thereby affecting its binding. It does not change the Vmax for the reaction, because it can’t affect the Enzyme-substrate complex.
Q.6
Answer: Option D.
Explanation: With increase in the concentration of substrate, the velocity of the enzyme-catalysed reaction levels off because all of the available enzyme in the reaction becomes saturated and then can no longer go any faster.
Q.7
Answer: Option E.
Explanation: Tertiary structure is the folded structure of a protein. Whenever there is a modification in the tertiary structure of a protein, it affects the active site of the protein thereby affecting the binding affinity and induced fit for the substrate.