Biology

Cellular Respiration and Enzymes

1,721 Questions

Explore key concepts of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain. These questions also cover ATP production, anaerobic respiration, and essential metabolic pathways. This topic forms a core part of the biology syllabus for many competitive examinations.

Glycolysis and metabolic pathwaysKrebs cycle processesElectron transport chainATP production countAnaerobic respiration products

Cellular Respiration and Enzymes Questions

Multiple choice

Which of the following enzymes acts on peroxide as an acceptor?

  1. Superoxide dismutase

  2. Cytochrome c oxidase

  3. Nitrate reductase

  4. Catalase

  5. Glutathione reductase
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Catalase belongs to Category EC 1.11 of oxidoreductases (EC 1), which act on peroxide as an acceptor. Catalase catalyses the decomposition of hydrogen peroxide to water and oxygen.

Multiple choice

Which of the following enzymes acts on the aldehyde or oxo group of donors?

  1. Pyruvate dehydrogenase

  2. Alcohol dehydrogenase

  3. NADH dehydrogenase

  4. Malate dehydrogenase

  5. Glycerol dehydrogenase
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pyruvate dehydrogenase belongs to Category EC 1.2 of oxidoreductases (EC 1), which act on the aldehyde or oxo group of donors. Pyruvate dehydrogenase performs the first two reactions within the pyruvate dehydrogenase complex: decarboxylation of pyruvate and reductive acetylation of lipoic acid.

Multiple choice

Dehydrogenase subclass of enzymes belongs to the class

  1. hydrolase

  2. oxidoreductase

  3. ligase

  4. transferase

  5. isomerase
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Oxidoreductase class of enzymes acts as catalysts in reactions involving oxidation-reduction. Subclasses belonging to this type of enzymes include oxidase, hydroxylases, oxygenases, peroxidases, dehydrogenase, reductase, etc.

Multiple choice

Which type of ATPases hydrolyse extracellular ATP?

  1. A-type ATPases

  2. P-type ATPases

  3. E-type ATPases

  4. V-type ATPases

  5. F-type ATPases
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

E-type ATPases (stands for ‘Extracellular’) are the class of cell surface enzymes which hydrolyse NTPs like extracellular ATP and NDPs. The most likely substrates are extracellular ATP, UTP, ADP and ATP.

Multiple choice

ATP synthasome is

  1. another name for ATP synthase

  2. used for reoxidation of malate to oxaloacetate

  3. used for converting ribose 5-phosphate into glyceraldehyde 3-phosphate

  4. used for forming ATP from ADP and Pi

  5. phosphate translocase and adenine nucleotide translocase taken together
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Phosphate translocase is second transport system. It is a symporter which transfers one H+ and one H2PO4- into matrix. Adenine nucleotide translocase is first transport system. It is combined in inner mitochondrial membrane. It is a membrane protein (antiporter) which is used for carrying Pi and ADP into matrix and ATP into cytosol. Both  the translocases taken together are known as ATP synthasome.

Multiple choice

Which one of the following is an inhibitor of FO portion of ATP synthase?

  1. Fluoro-aluminate

  2. Azide

  3. Tentoxin

  4. DCCD

  5. Efrapeptin
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

DCCD is an inhibitor of FO portion of ATP synthase. DCCD stands for Dicyclohexylcarbodiimide is an organic molecule by which protonated carboxyl groups can be covalently modified. DCCD, when combined with ATP synthase, reacts with carboxyl group of residual amino acid of subunit c at pH greater than 8 and hence, protonated at such high pH.

Multiple choice

Malonic acid affects succinic dehydrogenase for oxidising succinic acid. Malonic acid is a

  1. non-competitive inhibitor

  2. feedback inhibitor

  3. suicide inhibitor

  4. competitive inhibitor

  5. uncompetitive inhibitor
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Malonic acid is an example of competitive inhibitor because malonic acid affects succinic dehydrogenase for oxidising succinic acid to fumaric acid. The enzyme succinic dehydrogenase is prevented by malonic acid due to its structural similarity with succinic acid. Therefore, there is a competition between malonic acid and succinic acid for binding on the active site of the enzyme succinic dehydrogenase.

Multiple choice

Directions: For naming and classification of enzymes, IUB has created a systematic method. They have classified the enzymes depending on the kind of reactions the enzymes catalyse. The enzymes are classified into 6 classes.

Which of the following enzymes are responsible for catalysing the breaking down of substrate by hydrolysis?

  1. Isomerases

  2. Lyases

  3. Hydrolases

  4. Ligases

  5. Transferases
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Hydrolases are those enzymes which are responsible for catalysing the substrate’s lysis with the addition of water or by hydrolysis. They help to transfer the functional group towards water. Some of the substrates are peptide, ester, halide, glycosyl, etc.

Multiple choice

Directions: The process by which enzymes are converted to inactive substances with the help of compounds thereby severely affecting the enzymatically catalysed reaction rate is called enzyme inhibition.

Which type of inhibition takes place at the enzyme’s active site?

  1. Competitive inhibition

  2. Feedback inhibition

  3. Uncompetitive inhibition

  4. Non-competitive inhibition

  5. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Competitive inhibition takes place at the enzyme’s active site. The inhibitor’s structure bears close resemblance with the structure of substrate. It forms EI complex instead of ES complex after combining with the enzyme.

Multiple choice

Directions: The process by which enzymes are converted to inactive substances with the help of compounds thereby severely affecting the enzymatically catalysed reaction rate is called enzyme inhibition.

Sulpha drugs play an important role in the metabolism of p-amino benzoic acid. These drugs follow the standard of

  1. non-competitive inhibition

  2. feedback inhibition

  3. suicide inhibition

  4. competitive inhibition

  5. uncompetitive inhibition
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Antibacterial drugs like sulpha drugs are competitive inhibitors which play an important role in the metabolism of p-amino benzoic acid or PABA. Bacteria synthesise folic acid from p-amino benzoic acid. Sulpha drugs are structurally similar to PABA and therefore sulpha drugs behave as the enzyme inhibitor and are placed at the enzyme’s active site.

Multiple choice

ATP is produced in mitochondria as a result of oxidative phosphorylation and transferred to the cytoplasm but inner membrane of mitochondria is impenetrable to charged species. Two transport systems are used for transferring Pi and ADP into the matrix. ATP is transferred to the cytosol.

What is the function of ATP synthase?

  1. It is used for catalysing reversibly the formation of l-malic acid from glyoxylate and acetyl-CoA.

  2. It transfers one H+ and one H2PO4- into matrix.

  3. It reduces oxaloacetate to malate in gluconeogenesis.

  4. It acts as the catalyst during isomerisation of ribulose 5-phosphate to ribose 5-phosphate.

  5. It acts as the catalyst to form ATP using ADP and Pi.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

ATP synthase is a complex mitochondrial enzyme that is enclosed in a membrane. It acts as the catalyst to form ATP from ADP and Pi and also helps to transfer protons from positive side (intermembrane space) to the negative side (matrix) of the membrane.

Multiple choice

ATP is produced in mitochondria as a result of oxidative phosphorylation and transferred to the cytoplasm but inner membrane of mitochondria is impenetrable to charged species. Two transport systems are used for transferring Pi and ADP into the matrix. ATP is transferred to the cytosol.

Which of the following is the first transport system?

  1. Phosphate translocase

  2. Adenine nucleotide translocase

  3. Malate synthase

  4. Malate dehydrogenase

  5. Phosphopentose isomerase
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Adenine nucleotide translocase is the first transport system. It is combined in inner mitochondrial membrane. It is a membrane protein (antiporter) which is used for carrying Pi and ADP into matrix and ATP into cytosol.