Free Enzymes MCQs with Answers
633 Enzymes MCQs from Biology, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
Enzymes are biological catalysts that lower activation energy without being consumed, and their specificity is explained by the lock and key and induced fit models. Work includes the effects of temperature, pH and substrate concentration on reaction rate, plus competitive and non-competitive inhibition and how these differ.
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- A. released when the products are formed
- B. stored in the bonds of the substrate
- C. needed to bring the reactants to the transition state so the reaction can proceed
- D. used by the enzyme to bind the substrate
Explanation: Even an energetically favourable reaction needs an initial input to break existing bonds and reach the unstable transition state, and that…
Correct answer: needed to bring the reactants to the transition state so the reaction can proceed- A. coenzyme
- B. cofactor
- C. prosthetic group
- D. zymogen
Explanation: A zymogen, or proenzyme, carries an extra length of polypeptide that blocks the active site, and removing it activates the enzyme once it…
Correct answer: zymogen- A. dehydrogenase
- B. hydrolase
- C. isomerase
- D. ligase
Explanation: Enzymes are usually named from the substrate or the reaction plus the suffix ase, so a dehydrogenase removes hydrogen, as succinate…
Correct answer: dehydrogenase- A. independent of enzyme concentration
- B. directly proportional to the enzyme concentration
- C. inversely proportional to the enzyme concentration
- D. zero
Explanation: With substrate always available, every additional enzyme molecule adds its own turnover to the total, so doubling the enzyme doubles the…
Correct answer: directly proportional to the enzyme concentration- A. always occurs at the active site only
- B. can be reversed by adding more substrate
- C. involves the loss of the enzyme's three dimensional shape and is usually permanent
- D. increases the rate of the reaction
Explanation: Denaturation unfolds the whole protein, so the enzyme is destroyed as a catalyst and no amount of substrate will restore it, whereas most…
Correct answer: involves the loss of the enzyme's three dimensional shape and is usually permanent- A. starch into maltose
- B. protein into amino acids
- C. fat into fatty acids and glycerol
- D. hydrogen peroxide into water and oxygen
Explanation: A single catalase molecule can decompose millions of molecules of hydrogen peroxide per minute, which is necessary because the peroxide…
Correct answer: hydrogen peroxide into water and oxygen- A. a cofactor
- B. a coenzyme
- C. a prosthetic protein
- D. a substrate
Explanation: Cofactor is the term for an inorganic helper, and zinc in carbonic anhydrase and magnesium in the kinases of respiration are standard…
Correct answer: a cofactor- A. minerals absorbed from the soil
- B. vitamins of the B group
- C. fatty acids stored in adipose tissue
- D. the amino acids of the enzyme itself
Explanation: NAD is made from niacin, FAD from riboflavin and coenzyme A from pantothenic acid, so a deficiency of these vitamins cripples respiration…
Correct answer: vitamins of the B group- A. immobilised enzymes work at a much lower temperature
- B. immobilisation changes their specificity
- C. the enzyme can be recovered and reused and does not contaminate the product
- D. immobilised enzymes need no substrate
Explanation: Fixing the enzyme to beads or a membrane lets the product flow past and be collected pure, while the expensive enzyme stays behind for the…
Correct answer: the enzyme can be recovered and reused and does not contaminate the product- A. raises Vmax and leaves Km unchanged
- B. raises both Vmax and Km
- C. lowers Km and leaves Vmax unchanged
- D. lowers Vmax and leaves Km unchanged
Explanation: Because the inhibitor binds elsewhere and cannot be displaced by substrate, a fraction of the enzyme is permanently out of action, so the…
Correct answer: lowers Vmax and leaves Km unchanged- A. trypsin
- B. DNA polymerase
- C. catalase
- D. RNA polymerase
Explanation: The pancreas exports trypsin into the duodenum, where it digests food outside any cell.
Correct answer: trypsin32. The protein part of a conjugated enzyme, which on its own is catalytically inactive, is called the
- A. prosthetic group
- B. apoenzyme
- C. holoenzyme
- D. co-substrate
Explanation: The apoenzyme needs its non-protein partner, the cofactor, to become the active holoenzyme.
Correct answer: apoenzyme- A. lipid molecules with enzyme activity
- B. synthetic polymers made in the laboratory
- C. RNA molecules that catalyse reactions
- D. proteins permanently fixed to ribosomes
Explanation: The discovery that certain RNA molecules can catalyse reactions, such as self splicing, showed that not all enzymes are proteins.
Correct answer: RNA molecules that catalyse reactions- A. -ose
- B. -in
- C. -ol
- D. -ase
Explanation: Enzyme names end in -ase added to the substrate or reaction type, giving urease, lipase and dehydrogenase.
Correct answer: -ase- A. instability at body temperature
- B. gradual consumption during the reaction
- C. very high turnover number
- D. resistance to all inhibitors
Explanation: The turnover number is how many substrate molecules one enzyme molecule converts per second, and carbonic anhydrase has one of the highest…
Correct answer: very high turnover number36. Enzymes that catalyse the splitting of bonds with the addition of water belong to the class called
- A. hydrolases
- B. ligases
- C. transferases
- D. isomerases
Explanation: Hydrolases, such as amylase, lipase and peptidase, break bonds by inserting water.
Correct answer: hydrolases- A. They are consumed during the reaction
- B. They allow energetically impossible reactions to occur
- C. They increase the energy content of the products
- D. They are regenerated unchanged at the end of the reaction
Explanation: An enzyme leaves the reaction exactly as it entered, which is why tiny amounts can process huge quantities of substrate.
Correct answer: They are regenerated unchanged at the end of the reaction- A. permanently denatures the enzymes of microbes
- B. greatly reduces the rate of enzyme controlled reactions
- C. kills all bacteria and fungi at once
- D. changes the pH of the food
Explanation: Cold reduces the kinetic energy of molecules so enzyme catalysed spoilage reactions slow dramatically, but the enzymes are not destroyed…
Correct answer: greatly reduces the rate of enzyme controlled reactions- A. allosteric site
- B. active site
- C. cofactor site
- D. regulatory site
Explanation: The active site is a cleft formed by the folding of the chain, whose shape and chemistry fit the substrate.
Correct answer: active site- A. the active site is completely rigid
- B. the substrate changes its shape before binding
- C. enzymes have no binding site at all
- D. the active site moulds itself around the substrate as it binds
Explanation: Koshland argued in 1966 that binding itself induces a conformational change that tightens the fit and stresses bonds in the substrate…
Correct answer: the active site moulds itself around the substrate as it binds