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 functions is performed by biotin?

  1. Conversion of pyruvate to acetyl CoA

  2. Acts as a coenzyme for acetyl-CoA carboxylase

  3. Beta-oxidation of fatty acids

  4. Metabolism of nucleic acids
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Biotin is a critical coenzyme for acetyl CoA carboxylase, which is involved in the synthesis of fatty acids from acetate.

Multiple choice

Which one of the following is an inhibitor of oxidative phosphorylation?

  1. Fluroacetate

  2. Arsenite

  3. Malonate

  4. Piercidin A

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

Piercidin A inhibits NADH-CoQ reductase (Complex I) to block electron flow from the latter to CoQ. So oxidations of substrates such as pyruvate, isocitrate, α-ketogluterate, malate and 3-hudroxybutyrate, whose electrons enter the respiratory chain through complex I are prevented.

Multiple choice

The rate limiting step of glycolysis is controlled by

  1. Pfk - I

  2. Pfk - II

  3. Glyceraldehyde-3-phosphate dehydrogenase

  4. Hexokinase

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

Physiological concentration of ATP in cell inhibits Pfk-I allosterically and reduces its substrate affinity for fructose 6 phosphate. A 20% fall in ATP concentration rises the the rate of glycolysis 10-fold and Pfk activity to 50%. So low ATP/AMP ratio regulates the Pfk-I activity and thus, regulates glycolysis. Thus, Pfk-I is the enzyme for rate limiting step of glycolysis.

Multiple choice

In complex III, electrons are transferred _________.

  1. from NADH to CoQ

  2. from QH2 to Cytochrome C

  3. from FAD to CoQ

  4. from cytochrome C to O2

  5. from FMN to CoQ
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In complex III, electrons are transferred from ubiquinol (QH2) to cytochrome c by the enzyme cytochrome c reductase.

Multiple choice

Which of the following are yielded in a citric acid cycle?

  1. 3 NADH and 2 CO2

  2. 6 NADH and 2 CO2

  3. 6 NADH and 4 CO2

  4. 2 NADH and 4 CO2

  5. 2 NADH and 2 CO2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

NADH is yielded in three steps- (a) oxidation of isocitrate to oxalosuccinate (b) oxidation of α-ketogluterate to succinyl CoA and (c) oxidation of malate to oxaloacetate. Thus, 3 NADH molecules are formed and CO2 is produced during conversion of oxalosuccinate to α-ketogluterate and the latter to succinyl CoA. So in 1 cycle 3 NADH and 2 CO2 are formed.

Multiple choice

The final product of β-oxidation of a 16-carbon fatty acid is ________.

The metabolism of fatty acids occur by α and β-oxidation.

  1. 2 molecules of acetyl CoA

  2. 1 acetyl CoA and 14-carbon fatty acyl CoA

  3. Two acyl CoA

  4. 1 acetyl CoA

  5. 1 acyl CoA
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In each β-oxidation cycle, 2 carbons are lessoned from a fatty acyl CoA for the production of 1 molecule of acetyl CoA. In this way a 16-carbon fatty acid is oxidized by reduction of 2 carbon atoms at each cycle and finally the last fatty acyl CoA is none other than an acetyl CoA.

Multiple choice

Match the following: Pathways and rate limiting enzymes P. Glycogenesis a. Carbamoyl phosphate synthetase Q. Urea synthesis b. α-ketogluterate dehydrogenase R. TCA cycle c. Acetyl CoA carboxylase S. Purine Biosynthesis d. Glycogen synthase T. Fatty acid synthesis e. Glutamyl amido transferase

  1. P - a, Q - b, R - c, S - d, T - e

  2. P - d, Q - a, R - c, S - d, T - e

  3. P - d, Q - a, R - b, S - e, T - c

  4. P - e, Q - a, R - c, S - b, T - d

  5. P - a, Q - c, R - b, S - d, T - e
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rate limiting enzyme for glycogenesis is glycogen synthase,urea is carbamoyl phosphate synthetase, TCA cycle is α-ketogluterate dehydrogenase, purine biosynthesis is glutamyl amido transferase and fatty acid synthesis is Acetyl CoA carboxylase.

Multiple choice

Active glycogen synthase is converted to inactive form by phosphorylation of ____________.

Glycogen synthase enzyme catalyses the rate limiting step of glycogenesis.

  1. proline residues

  2. tyrosine residues

  3. serine residues

  4. threonine residues

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

Active glycogen synthase a is converted to inactive form glycogen synthase b by phosphorylation of its seven serine residues with ATP by different cAMP dependent protein kinase enzymes.

Multiple choice

The number of ATP molecules produced from a 16 carbon fatty acid is _______________.

The metabolism of fatty acids occur by α and β-oxidation.

  1. 129

  2. 131

  3. 106

  4. 108

  5. 130
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The ATP yield for every oxidation cycle is theoretically at maximum yield 17, as NADH produces 3 ATP, FADH2 produces 2 and a full rotation of the Citric Acid Cycle produces 12. In practice it is closer to 14 ATP for a full oxidation cycle as in practice the theoretical yield isn't attained, it's generally closer to 2.5 ATP per NADH molecule produced, 1.5 for each FADH2 Molecule produced and this equals to 10 per cycle of the TCA (according to the P/O ratio)Source ATP Total1 FADH2x 1.5 ATP = 1.5 ATP (Theoretically 2 ATP)1 NADHx 2.5 ATP = 2.5 ATP (Theoretically 3 ATP)1 acetyl CoAx 10 ATP = 10 ATP (Theoretically 12 ATP)TOTAL = 14 ATPFor a 16-carbon fatty acid, the number of ATPs generated:Source ATP Total7 FADH2 x 1.5 ATP = 10.5 ATP7 NADH x 2.5 ATP = 17.5 ATP8 acetyl CoA x 10 ATP = 80 ATP. Activation = -2 ATPNET = 106 ATPIn the first step of β-oxidation, the acyl CoA produced from a 16-C saturated fatty acid is transferred to mitochondria by carnitine carriers at the cost of 2 ATPs. So the net energy yield is 106 ATPs at the end of one complete β-oxidation of a 16-C fatty acid.

Multiple choice

Assertion (A): During aerobic respiration, lesser number of ATPs is produced in eukaryotes than in prokaryotes. Reason (R): In eukaryotes, some energy is lost when electrons are shuttled across the mitochondrial membranes that separate glycolysis (in cytoplasm) from the electron transport chain.

Directions: In the following question, there are two statements, Assertion (A) and Reason (R). Consider both the statements independently and mark your answers as under:

1. A and R both are correct and R is the correct explanation of A.
2. A and R both are correct and R is not the correct explanation of A.
3. A is correct and R is incorrect.
4. A is incorrect and R is correct.
5. A and R both are incorrect.

  1. A and R both are correct and R is the correct explanation of A.

  2. A and R both are correct and R is not the correct explanation of A.

  3. A is correct and R is incorrect.

  4. A is incorrect and R is correct.

  5. A and R both are incorrect.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

During aerobic respiration, lesser number of ATPs is produced in eukaryotes (34 molecules of ATP) than in prokaryotes (38 molecules of ATP). This is because of the reason that, In eukaryotes some energy is lost when electrons are shuttled across the mitochondrial membranes that separate glycolysis (in cytoplasm) from the electron transport chain. No such separate mechanism exists in prokaryotes.