Free NEET Biology multiple-choice questions on Enzymes. Attempt each question and reveal the answer with a full explanation.
Identify the incorrect statement regarding enzymes. Enzymes increase the activation energy of a reaction. Most enzymes are proteins. Enzymes are highly specific for their substrates. Enzymes lower the activation energy of a reaction. The cofactor of the enzyme carboxypeptidase is: Zinc Niacin Flavin Haem Inhibition of Succinic dehydrogenase enzyme by malonate is a classical example of: Cofactor inhibition Feedback inhibition Competitive inhibition Enzyme activation Regarding catalytic cycle of an enzyme action, select the correct sequential steps : A. Substrate enzyme complex formation. B. Free enzyme ready to bind with another substrate. C. Release of products. D. Chemical bonds of the substrate broken. E. Substrate binding to active site. Choose the correct answer from the options given below : E, A, D, C, B A, E, B, D, C B, A, C, D, E E, D, C, B, A The protein portion of an enzyme is called: Prosthetic group Cofactor Coenzyme Apoenzyme Which one of the following enzymes contains ‘Haem’ as the prosthetic group? Catalase RuBisCo Carbonic anhydrase Succinate dehydrogenase Name the class of enzyme that usually catalyze the following reaction : S-G + S S + S -G Where, G a group other than hydrogen S a substrate S another substrate Ligase Hydrolase Lyase Transferase Which of the following describes the 'Lock and Key' hypothesis of enzyme action? The active site is a rigid structure exactly complementary to the substrate. The active site changes shape to fit the substrate. The substrate changes shape to fit the enzyme. The enzyme is destroyed after the reaction. A complete catalytic enzyme with its bound co-factor is called a/an Holoenzyme Apoenzyme Co-enzyme Prosthetic group Which of the following describes the relationship between enzyme activity and temperature? Activity increases with temperature, reaches an optimum, and then declines. Activity increases linearly with increasing temperature. Activity decreases linearly with increasing temperature. Activity is independent of temperature changes. The prosthetic group of the enzyme peroxidase, which catalyzes the breakdown of hydrogen peroxide, is: Haem NAD FAD Zinc Enzymes increase the rate of a chemical reaction by: Lowering the activation energy Increasing the temperature of the system Changing the equilibrium constant Decreasing the free energy of the products The transition state structure of the substrate formed during an enzymatic reaction is: Transient and unstable Permanent and stable Transient but stable Permanent but unstable Which class of enzymes is responsible for joining together two compounds, such as C-O , C-S , C-N , or P-O bonds? Ligases Lyases Hydrolases Transferases Enzymes that catalyze the linking together of two compounds (e.g., C-O or C-N bonds) using energy from ATP are classified as: Ligases Lyases Hydrolases Transferases Which of the following graphs correctly represents the effect of pH on enzyme activity? A bell-shaped curve A linear upward slope A hyperbolic curve A sigmoidal curve Which of the following is an example of an inorganic cofactor that forms coordination bonds with both the substrate and the enzyme's active site? Zn 2+ in Carboxypeptidase Mg 2+ in Hexokinase Fe 2+ in Catalase NAD in Dehydrogenase Which type of protein structure is represented by the 'Heme' group in myoglobin? Prosthetic group Apoenzyme Co-enzyme Primary structure The K m value (Michaelis constant) of an enzyme is a measure of its: Affinity for its substrate Maximum velocity ( V max ) Optimal temperature Activation energy Enzymes that catalyze the hydrolysis of ester, ether, peptide, glycosidic, C-C , C-halide or P-N bonds are grouped under which class? Hydrolases Ligases Lyases Transferases Which of the following describes the 'saturation effect' in enzyme kinetics? The velocity of the reaction reaches a maximum ( V max ) when all enzyme active sites are occupied by substrate. The enzyme activity decreases when substrate concentration is too high. The K m value increases as more substrate is added. The reaction stops once the substrate concentration equals the enzyme concentration. The effect of a competitive inhibitor can be reversed by: Increasing the substrate concentration Decreasing the substrate concentration Increasing the inhibitor concentration Adding a non-competitive inhibitor Which of the following statements regarding enzyme inhibition is correct - Competitive inhibition is seen when a substrate competes with an enzyme for binding to an inhibitor protein Non-competitive inhibitors often bind to the enzyme irreversibly Competitive inhibition is seen when the substrate and the inhibitor compete for the active site on the enzyme Non-competitive inhibition of an enzyme can be overcome by adding large amount of substrate What is the role of competitive inhibitors during enzyme action? It competes with the substrate for the active site of the enzyme It binds to the enzyme-substrate complex It changes the shape of the enzyme by binding to an allosteric site It increases the activation energy requirement Which of the following co-factors is transiently bound to the apoenzyme? Co-enzymes Prosthetic groups Metal ions Holoenzymes The inhibition of succinate dehydrogenase by malonate is an example of Competitive inhibition Non-competitive inhibition Allosteric inhibition Negative feedback The Michaelis-Menten constant ( K m ) is the substrate concentration at which the reaction velocity is 1 2 V max V max 1 4 V max Zero The enzyme-substrate ( E-S ) complex is a highly reactive, short-lived structure. The concept of the 'induced fit' model of enzyme action was proposed by Koshland Emil Fischer Singer and Nicolson Watson and Crick Which class of enzymes catalyzes the removal of groups from substrates by mechanisms other than hydrolysis, leaving double bonds? Lyases Hydrolases Ligases Transferases In competitive inhibition, the inhibitor affects the enzyme's kinetics by: Increasing K m and keeping V max constant Decreasing K m and decreasing V max Increasing K m and increasing V max Keeping K m constant and decreasing V max Which of the following is an example of an allosteric inhibitor that binds to an enzyme at a site other than the active site? Non-competitive inhibitor Competitive inhibitor Co-factor Apoenzyme In a competitive inhibition, the inhibitor (I) competes with the substrate (S) for the active site. What effect does this have on the V max and K m of the enzyme? V max remains unchanged, K m increases V max decreases, K m remains unchanged Both V max and K m decrease V max increases, K m remains unchanged Feedback inhibition, a common regulatory mechanism in metabolic pathways, usually involves the end product acting as a/an: Allosteric inhibitor Competitive inhibitor Co-enzyme Apoenzyme An organic substance bound to an enzyme and essential for its activity is called - Coenzyme Holoenzyme Apoenzyme isoenzyme The enzyme complex that catalyzes the transfer of a group ( G ) other than hydrogen between a pair of substrates is categorized under: Transferases Ligases Lyases Isomerases A non-proteinaceous enzyme is Ribozyme Ligase Deoxyribonuclease Lysozyme The enzyme which catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate is an example of which class? Isomerases Transferases Lyases Ligases Which class of enzymes is involved in the conversion of glucose into its isomer, fructose, during glycolysis? Isomerases Transferases Lyases Ligases Which of the following substances acts as a competitive inhibitor of the enzyme succinate dehydrogenase in the Krebs cycle? Malonate Oxaloacetate α -ketoglutarate Malate The enzyme Carbonic Anhydrase contains which of the following metal ions as a cofactor at its active site? Zn 2+ Mg 2+ Fe 2+ Cu 2+ The catalytic efficiency of two different enzymes can be compared by the - The Km value The pH optimum value Molecular size of the enzyme Formation of the product Select the option which is not correct with respect to enzyme action :- Substrate binds with enzyme at its active site. Addition of lot of succinate does not reverse the inhibition of succinic dehydrogenase by malonate. A non-competitive inhibitor binds the enzyme at a site distinct from that which binds the substrate. Malonate is a competitive inhibitor of succinic dehydrogenase. Which of the following statements regarding enzyme inhibition is correct? Non competitive inhibitors often bind to the enzyme irreversibly Competitive inhibition is seen when substrate competes with an enzyme for binding to an inhibition protein. Competitive inhibition is seen when the substrate and the inhibitor compete. Non competitive inhibition of an enzyme can be overcome by adding large amount of substrate. Consider the following statement : (A) Coenzyme or metal ion that is tightly bound to enzyme protein is called prosthetic group. (B) A complete catalytic active enzyme with its bound prosthetic group is called apoenzyme. Select the correct option. (A) is false but (B) is true. Both (A) and (B) are true. (A) is true but (B) is false. Both (A) and (B) are false. Transition state structure of the substrate formed during an enzymatic reaction is Transient but stable Permanent but unstable Transient and unstable Permanent and stable Melonate inhibits the growth of pathogenic bacteria by inhibiting the activity of Succinic dehydrogenase Amylase Lipase Dinitrogenase The following reaction depicts the activity of a particular class of enzymes : Identify the enzymes class ‘E’ from the following options : Isomerases Ligases Transferases Lyases The catalytic efficiency of two different enzymes can be compared by their: K m value Molecular weight pH optimum Formation of product Which of the following is a non-competitive inhibitor that binds to the enzyme at a site other than the active site, thereby decreasing the V max without changing the K m ? Cyanide Malonate Succinate DDT Which of the following enzymes is not protein ? Ribozyme Polymerase Ligase Lysozyme Enzymes that utilize ATP in phosphate transfer require an alkaline earth metal (M) as the cofactor. M is : Sr Be Mg Ca The incorrect statement regarding enzymes is Like chemical catalysts enzymes reduce the activation energy of bio processes. Enzymes are polysaccharides. Enzymes are very specific for a particular reaction and substrate. Enzymes are biocatalysts. Given below are two statements : Statement I : Low temperature preserves the enzyme in a temporarily inactive state whereas high temperature destroys enzymatic activity because proteins are denatured by heat. Statement II : When the inhibitor closely resembles the substrate in its molecular structure and inhibits the activity of the enzyme, it is known as competitive inhibitor. In the light of the above statements, choose the correct answer from the options given below : (1) Both Statement I and Statement II are true. (2) Both Statement I and Statement II are false. (3) Statement I is true but Statement II is false. (4) Statement I is false but Statement II is true.