Bioenergetics MCQ Quiz in मराठी - Objective Question with Answer for Bioenergetics - मोफत PDF डाउनलोड करा

The correct answer is B, D, and E

Explanation:

Statement A: Complex I (NADH: ubiquinone oxidoreductase) transfers electrons from NADH to oxygen.

• This statement is incorrect. Complex I, also known as NADH: ubiquinone oxidoreductase, transfers electrons from NADH to ubiquinone (Coenzyme Q), not directly to oxygen.
• In the electron transport chain, oxygen is the final electron acceptor, but it receives electrons via Complex IV, not Complex I. Complex I passes electrons from NADH to ubiquinone, which is then reduced to ubiquinol (QH₂). This process is also coupled with the pumping of protons (H⁺) from the mitochondrial matrix into the intermembrane space.

Statement B: Complex II (succinate dehydrogenase) transfers electrons from succinate to ubiquinone (Coenzyme Q).

• This statement is correct. Complex II (also known as succinate dehydrogenase) plays a dual role in the citric acid cycle and the electron transport chain.
• In the citric acid cycle, it catalyzes the conversion of succinate to fumarate, producing FADH₂. In the ETC, Complex II transfers the electrons from FADH₂ (produced in the citric acid cycle) to ubiquinone (Coenzyme Q). However, unlike Complex I, it does not pump protons across the membrane.

Statement C: The flow of electrons through Complex III pumps protons into the mitochondrial matrix.

• This statement is incorrect. Complex III (cytochrome bc₁ complex) pumps protons into the intermembrane space, not into the matrix. In the ETC, the primary role of Complex III is to transfer electrons from ubiquinol (QH₂) to cytochrome c while contributing to the generation of the proton gradient by pumping protons from the matrix to the intermembrane space. This proton gradient across the inner mitochondrial membrane drives ATP synthesis via ATP synthase.

Statement D: Complex IV (cytochrome c oxidase) catalyzes the transfer of electrons from cytochrome c to molecular oxygen.

• This statement is correct. Complex IV, also known as cytochrome c oxidase, is the terminal complex in the electron transport chain. It accepts electrons from cytochrome c and catalyzes the transfer of these electrons to molecular oxygen (O₂), the final electron acceptor in the chain. This results in the formation of water (H₂O). This step is essential for the maintenance of the proton gradient across the inner mitochondrial membrane.

Statement E: ATP synthase uses the proton gradient across the inner mitochondrial membrane to drive the synthesis of ATP from ADP and inorganic phosphate (Pi).

• This statement is correct. ATP synthase (Complex V) is a critical enzyme in oxidative phosphorylation. It uses the energy stored in the proton gradient (established by the ETC) across the inner mitochondrial membrane to drive the synthesis of ATP. Protons flow back into the mitochondrial matrix through ATP synthase, a process called chemiosmosis, which provides the energy needed to convert ADP and inorganic phosphate (Pi) into ATP.

The correct answer is B and D 

Explanation:

A. Increased blood glucose would decrease gluconeogenesis and increase glycogen synthesis: This statement is correct. When blood glucose levels are high, the body tends to store glucose as glycogen and reduce the production of glucose through gluconeogenesis. Insulin is released, which promotes glycogen synthesis (glycogenesis) and decreases gluconeogenesis.

B. Increased levels of fructose-1, 6-bisphosphate inhibit glycolysis: This statement is incorrect. Fructose-1,6-bisphosphate is an intermediate in glycolysis and generally acts to stimulate the process rather than inhibit it. In glycolysis, fructose-1,6-bisphosphate is formed from fructose-6-phosphate and later split into two three-carbon sugars that continue through the glycolytic pathway.

C. Increased blood glucagon inhibits glycogen synthesis and stimulates glycogen breakdown: This statement is correct. Glucagon is a hormone that is released when blood glucose levels are low. It signals the liver to break down glycogen into glucose (glycogenolysis) and to decrease glycogen synthesis. This increases blood glucose levels.

D. Increase in AMP levels inhibits glycolysis and stimulates gluconeogenesis: This statement is incorrect. AMP (adenosine monophosphate) is an indicator of low energy status in the cell. High levels of AMP activate glycolysis to produce ATP and inhibit gluconeogenesis, which consumes ATP.

Table: Regulators of Glycolysis

Conclusion: Therefore, the statements that are incorrect are B and D

The correct answer is Option 2 i.e. 3 NADH + 1 FADH2 + 1 GTP

Concept:

• Aerobic cellular respiration is made up of three parts: glycolysis, the citric acid (Krebs) cycle, and oxidative phosphorylation.
• In glycolysis, glucose metabolizes into two molecules of pyruvate, with an output of ATP and nicotinamide adenine dinucleotide (NADH).
• Each pyruvate oxidizes into acetyl CoA and an additional molecule of NADH and carbon dioxide (CO2).
• The acetyl CoA is then used in the citric acid cycle, which is a chain of chemical reactions that produce CO2, NADH, flavin adenine dinucleotide (FADH2), and GTP.
• In the final step, the three NADH and one FADH₂ amassed from the previous steps are used in oxidative phosphorylation, to make water and ATP.

These are the steps in cytric acid cycle: 

• Step 1: The first step is the condensation of acetyl CoA with 4-carbon compound oxaloacetate to form 6C citrate, coenzyme A is released. The reaction is catalysed by citrate synthase.
• Step 2: Citrate is converted to its isomer, isocitrate. The enzyme aconitase catalyses this reaction.
• Step 3: Isocitrate undergoes dehydrogenation and decarboxylation to form 5C α-ketoglutarate. A molecular form of CO₂ is released. Isocitrate dehydrogenase catalyses the reaction. It is an NAD⁺ dependent enzyme. NAD⁺ is converted to NADH.
• Step 4: 𝝰-ketoglutarate undergoes oxidative decarboxylation to form succinyl CoA, a 4C compound. The reaction is catalyzed by the α-ketoglutarate dehydrogenase enzyme complex. One molecule of CO₂ is released and NAD⁺ is converted to NADH.
• Step 5: Succinyl CoA forms succinate. The enzyme succinyl CoA synthetase catalyses the reaction. This is coupled with substrate-level phosphorylation of GDP to get GTP. GTP transfers its phosphate to ADP forming ATP.
• Step 6: Succinate is oxidised by the enzyme succinate dehydrogenase to fumarate. In the process, FAD is converted to FADH₂.
• Step 7: Fumarate gets converted to malate by the addition of one H₂O. The enzyme catalysing this reaction is fumarase.
• Step 8: Malate is dehydrogenated to form oxaloacetate, which combines with another molecule of acetyl CoA and starts the new cycle. Hydrogens removed, get transferred to NAD⁺ forming NADH. Malate dehydrogenase catalyses the reaction.

One turn of citric acid cycle produces 1GTP, 3 NADH, and 1 FADH₂ so, a total of 2 GTP, 6 NADH, and 2 FADH₂ are formed per glucose molecule as two citric acid cycles take place for each pyruvate molecule formed from a glucose molecule.

Explanation:

• Each pyruvate oxidizes into acetyl CoA and an additional molecule of NADH and carbon dioxide (CO₂).
• The acetyl CoA is then used in the citric acid cycle, which is a chain of chemical reactions that produce CO₂, NADH, flavin adenine dinucleotide (FADH₂), and GTP.
• One turn of citric acid cycle produces 1 GTP, 3 NADH, and 1 FADH₂
•  Total of 2GTP, 6 NADH, and 2 FADH₂ are formed per glucose molecule as two citric acid cycles take place for each pyruvate molecule formed from a glucose molecule.

​

Explanation:

Option 1:- 2 NADH + 2 FADH2 + 1 GTP  incorrect

One turn of citric acid cycle produces 1 ATP, 3 NADH, and 1 FADH2 

hence this option is incorrect.

Option 2:-  3 NADH + 1 FADH2 + 1 GTP  correct

The acetyl CoA used in the citric acid cycle, which is a chain of chemical reactions that produce CO2, NADH, flavin adenine dinucleotide (FADH2), and GTP. One turn of citric acid cycle produces 1 GTP, 3 NADH, and 1 FADH2. Total of 2GTP, 6 NADH, and 2 FADH2 are formed per glucose molecule as two citric acid cycles take place for each pyruvate molecule formed from a glucose molecule.

Hence this option is correct.

Option 3:- 3 NADH + 1 GTP incorrect

 This option is not have 1 FADH2  One turn of citric acid cycle produces 1 ATP, 3 NADH, and 1 FADH2

hence this option is incorrect.

Option 4:- 4 NADH + 1 FADH2 + 1 GTP incorrect

 this option have 4 NADH but  3 NADH is actually produce with 1 ATP, and 1 FADH2 as acetyl CoA used in the citric acid cycle.

hence this option is incorrect.

Hence Option 2 is correct option 

Concept:

• The oxidative phosphorylation process, also known as the electron transport chain, is a collection of four protein complexes that combine redox events to produce an electrochemical gradient that results in the production of ATP.
• Both photosynthesis and cellular respiration take place in mitochondria.
• In the former, energy is released together with the release of electrons from the breakdown of organic molecules.
• In the latter, after being activated by light, the electrons join the chain, and the energy released is used to create carbs.

Fig 1: ETS in mitochondria:

• Rotenone (a plant product commonly used as an insecticide) forms a complex with NADH dehydrogenase, inhibiting the oxidation of NADH to NAD and thus blocking the oxidation of glutamate, alpha-ketoglutarate, and pyruvate by NAD in the Electron transport system.

Fig 2: rotenone and ETS

Explanation:

Option 1: The P/O ratio is reduced from 3:1 to 2:1

•  P/O is the number of ATP molecules synthesized by oxidative phosphorylation for each pair of electrons (hence, not P/O2) passing from a particular substrate, typically NADH or succinate, via a respiratory chain, to O2. Knowledge of the P/O ratio is fundamental for understanding the ATP yield from cell fuels and is a core metabolic parameter.
• P:O = ADP phosphorylated molecules/ atoms of oxygen reduced
• Given the assumption that P/O has an integral value, most experimenters agreed that the P/O ratio for NADH must be 3. 
• However rotenone inhibits the ETS after NADH and consequently P/O ratio reduces from 3 to 2.
• This option is correct when the concept is taken into consideration as the P/O ratio is reduced

Option 2:  The rate of NADH oxidation is reduced to two-thirds of its initial value.

Fig 3: Path of electrons from NADH, succinate, fatty acyl–CoA, 
and glycerol 3-phosphate to ubiquinone.

• This option is false since NADH is reduced and not oxidized whereas other electron carriers get oxidized due to blockage of NADH dehydrogenase enzyme by Rotenone.

Option 3: Succinate oxidation remains normal

• The mitochondrial succinate dehydrogenase (SDH) complex catalyzes the oxidation of succinate to fumarate in the Krebs cycle, and feeds electrons to the respiratory chain ubiquinone (UQ) pool, however inhibition of Complex I (CI) by rotenone prevents accumulation of oxaloacetate which is a potent inhibitor of SDH. thus After inhibition of CI by rotenone, the oxidation of succinate increases due to excess of SDH.
• So this option is not true

Option 4: Electron flow is inhibited at complex II

• The succinate dehydrogenase enzyme (SDH) is also known as Complex II in the electron transport chain.
• Only FADH2 can supply it with electrons, which it then transfers to ubiquinone
•  ETC's only complex without a proton pump coupling is this one.
•  Rotenone can only inhibit NADH dehydrogenase and not FADH2 hence has no effect on the complex II system.
• Hence this option is untrue.

So the correct answer is option 1

The correct answer is B and D

Explanation:

Statement A: "High levels of glucose-6-phosphate inhibit glycolysis."

• Correct. High levels of glucose-6-phosphate signal that the cell has sufficient glucose and energy, which inhibits glycolysis to prevent the overconsumption of glucose and the production of pyruvate.

Statement B: "Increased concentrations of NADH stimulate gluconeogenesis."

• Incorrect. Increased levels of NADH actually favor glycolysis and inhibit gluconeogenesis. High NADH levels indicate a high energy state, promoting the conversion of glucose to pyruvate instead of the synthesis of glucose from non-carbohydrate precursors.

Statement C: "Increased glucagon levels lead to increased blood glucose by stimulating gluconeogenesis."

• Correct. Glucagon is a hormone that promotes gluconeogenesis in the liver, which increases blood glucose levels, especially during fasting or low-energy states.

Statement D: "Citrate accumulation signals the cell to increase glycolysis."

• Incorrect. Citrate is an intermediate of the citric acid cycle and serves as a signal that energy production is sufficient. High citrate levels actually inhibit glycolysis and stimulate gluconeogenesis and fatty acid synthesis instead.

Conclusion: The option that includes the INCORRECT statements is B and D

The correct answer is  Only Statements 1 and 2 are correct.

Explanation:

Statement 1: The enzyme phosphofructokinase (PFK-1) catalyzes the rate-limiting step in glycolysis and is allosterically regulated by AMP and ATP.

Phosphofructokinase-1 (PFK-1) is the most important regulatory enzyme in glycolysis. It catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate using ATP. This step is considered the rate-limiting step of glycolysis because it is highly regulated and controls the overall flux of the glycolytic pathway.

Allosteric regulation: PFK-1 is regulated by various molecules that reflect the energy state of the cell:

• AMP: Signals low energy levels and activates PFK-1 to increase glycolytic flux and generate more ATP.
• ATP: Signals high energy levels and inhibits PFK-1, thereby reducing glycolytic activity to prevent excessive ATP production.

Therefore, Statement 1 is correct.

Statement 2: Oxidative phosphorylation involves the transfer of electrons from NADH and FADH₂ to oxygen via the electron transport chain, coupled to ATP synthesis through a proton gradient.

Oxidative phosphorylation is the final stage of cellular respiration, occurring in the mitochondria. It involves two major components:

• Electron Transport Chain (ETC): Electrons from NADH and FADH₂ (produced in glycolysis, the citric acid cycle, and beta-oxidation) are transferred through a series of protein complexes (Complex I, II, III, and IV) embedded in the inner mitochondrial membrane. Oxygen is the final electron acceptor, forming water.
• Proton Gradient and ATP Synthesis: As electrons pass through the ETC, protons (H⁺ ions) are pumped from the mitochondrial matrix into the intermembrane space, creating a proton gradient. This gradient stores potential energy. The protons then flow back into the matrix through ATP synthase (Complex V), driving the synthesis of ATP from ADP and inorganic phosphate (Pi). This process is termed chemiosmosis.

Statement 3: In biological systems, group transfer reactions often involve the transfer of phosphate which play a significant role in metabolic pathways like glycolysis and the citric acid cycle.

This statement is incorrect because it suggests that group transfer reactions only involve the transfer of phosphate groups. While phosphate transfer (as seen in ATP hydrolysis and phosphorylation reactions) is critical, group transfer reactions also involve other types of groups such as methyl groups, acyl groups, and others. For example:

• Methyl transfer reactions are important in DNA methylation (regulation of gene expression).
• Acyl transfer reactions occur in the citric acid cycle where acetyl-CoA transfers an acetyl group to oxaloacetate.

Therefore, the correct statements are Statement 2 and 3

The correct answer is Flavin

Explanation:

In the electron transport chain (ETC), which is a series of electron carriers embedded in the inner mitochondrial membrane (or the cell membrane in prokaryotes) that facilitate the transfer of electrons from NADH and FADH₂ to oxygen, different types of electron carriers can transport one or two electrons.

• Cytochrome: Cytochromes are proteins that contain a heme group (an iron-containing porphyrin ring). They carry out one-electron transfers in the electron transport chain. The iron atom in the heme group alternates between Fe²⁺ (reduced form) and Fe³⁺ (oxidized form) as it accepts and donates electrons.
• Iron‐sulphur proteins (Fe‐S cluster): Iron-sulfur proteins contain clusters of iron and sulfur atoms that facilitate electron transfer. They typically perform one-electron transfers in the electron transport chain, with iron cycling between Fe²⁺ and Fe³⁺ states.
• Flavin: Flavins, such as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), are capable of undergoing two-electron transfers. They can be reduced or oxidized in two steps, each involving the transfer of one electron, ultimately allowing the transport of two electrons. This is due to their unique chemical structure, which can accommodate either one or two electrons.
• Cuproproteins: Cuproproteins contain copper ions as their electron-carrying cofactors. Like cytochromes, copper ions in cuproproteins usually undergo one-electron transfers, cycling between Cu⁺ (reduced) and Cu²⁺ (oxidized) states.

Thus, the correct answer is Flavin, due to its ability to carry two electrons as part of its normal function in the electron transport chain.

The correct answer is A and C

Concept:

• Pyruvate dehydrogenase is an important enzyme in cellular respiration that converts pyruvate into acetyl-CoA, a critical step linking glycolysis to the citric acid cycle.
• Feedback inhibition is a regulatory mechanism where the end products of a metabolic pathway inhibit an enzyme involved in that pathway, thus controlling the pathway's overall activity and maintaining homeostasis.
• In the case of pyruvate dehydrogenase, its activity is inhibited by its end products to prevent the overproduction of acetyl-CoA and NADH, which could disrupt cellular metabolic balance.

Fig: Pyruvate dehydrogenase complex reaction (Source)

Explanation:

• NADH: NADH is a product of the pyruvate dehydrogenase reaction. High levels of NADH indicate that the cell's energy needs are met, leading to feedback inhibition of pyruvate dehydrogenase to prevent the accumulation of excess acetyl-CoA and NADH.
• Acetyl-CoA: Acetyl-CoA is another product of the pyruvate dehydrogenase reaction. When acetyl-CoA levels are high, it signals that the citric acid cycle and downstream metabolic pathways have sufficient substrates, thereby inhibiting pyruvate dehydrogenase to prevent further production of acetyl-CoA.

Other Options:

•  FAD is not a direct product of the pyruvate dehydrogenase complex. While FAD is involved in other parts of cellular respiration (such as the citric acid cycle), it does not directly participate in the feedback inhibition of pyruvate dehydrogenase.
• Acetaldehyde is not a product of pyruvate dehydrogenase. It is involved in fermentation pathways under anaerobic conditions. Hence, it does not play a role in the feedback inhibition of pyruvate dehydrogenase.

The correct answer is A, B, D

​Explanation:

Pyruvate kinase (PK) is an enzyme that plays a crucial role in the final steps of glycolysis, which is the process of breaking down glucose to produce energy. PK catalyzes the conversion of phosphoenolpyruvate (PEP) to pyruvate, generating ATP in the process.

• ATP is an allosteric inhibitor of PK:  When ATP levels are high, it signals that the cell has sufficient energy, and thus the need for further ATP production via glycolysis decreases. ATP binds to an allosteric site on PK and inhibits its activity, preventing unnecessary breakdown of glucose. 
• Fructose 1,6-bisphosphate is an activator of PK: - Fructose 1,6-bisphosphate (F-1,6-BP) is an intermediate of glycolysis that acts as a feed-forward activator of PK. This ensures that the enzyme is activated when glycolysis is proceeding, promoting efficient energy production.
• Alanine is an allosteric modulator of PK: - Alanine is an amino acid that can signal the abundance of building blocks for protein synthesis. - When alanine levels are high, it inhibits PK activity as a feedback mechanism to prevent excess pyruvate production, which can be converted into alanine.

The correct answer is A-(iv), B-(i), C-(ii), D-(iii)

Concept:

• Oxidative phosphorylation is the process in cells through which ATP, the primary energy currency, is produced. This process takes place in the mitochondria and involves the electron transport chain (ETC) and ATP synthase.
• Various chemical agents can interfere with oxidative phosphorylation by targeting different components of the electron transport chain or ATP synthase, leading to the disruption of ATP production.

Explanation:

• Antimycin A (A): Blocks electron transfer from cytochrome b to cytochrome c1 (iv). This inhibition stops the electron flow in the ETC, halting ATP production.
• Oligomycin (B): Inhibits the F₀ component of ATP synthase (i). This prevents protons from passing through ATP synthase, stopping the synthesis of ATP.
• Valinomycin (C): Disrupts inner mitochondrial membrane potential (ii). By transporting potassium ions across the membrane, it dissipates the proton gradient, which is essential for ATP synthesis.
• Rotenone (D): Prevents electron transport from the Fe/S cluster to ubiquinone (iii). This action inhibits Complex I of the ETC, stopping electron flow and ATP production.