Energy Production and Metabolism Practice Questions

Q: Cancer cells preferentially utilize glycolysis for energy production even in the presence of adequate oxygen. What is this phenomenon called?

Warburg effect. ***Warburg*** - The **Warburg effect** describes how cancer cells preferentially use glycolysis for energy production even in the presence of oxygen, allowing them to thrive in **hypoxic conditions** [1]. - This metabolic adaptation supports **cell proliferation** and survival in tumor microenvironments where oxygen is limited [1][3]. - Cancer cells upregulate glucose uptake and express specific metabolic enzymes like the M2 isoform of pyruvate kinase that facilitate this altered metabolism [2][4]. *Wanton* - This term typically refers to recklessness or extravagance and is not used in the context of cancer metabolism or hypoxia. - There are no associations with **cancer cell adaptation** under adverse environmental conditions. *Wormian* - **Wormian bones** are extra bone pieces within sutures of the skull, unrelated to cancer cell metabolism or survival mechanisms. - This term does not connect to **hypoxia** or metabolic adaptations in cancer biology. *Wolf* - "Wolf" has no recognized connection to cancer cell biology, particularly regarding metabolic adaptations under **hypoxic stress**. - It does not imply any concept associated with how cancer cells cope with adverse conditions. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 307-308. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 308-310. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 290-291. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 26-27.

Q: What is the total number of dehydrogenases involved in the Krebs cycle?

4. ***4*** - There are four major **dehydrogenase enzymes** that catalyze oxidation-reduction reactions in the Krebs cycle. - These enzymes are **isocitrate dehydrogenase**, **α-ketoglutarate dehydrogenase complex**, **succinate dehydrogenase**, and **malate dehydrogenase**. *3* - This count is incorrect as it omits at least one key dehydrogenase involved in the Krebs cycle's oxidative steps. - A count of three would exclude one of the enzymes responsible for generating **NADH** or **FADH2**. *2* - This number is significantly underestimated, as the Krebs cycle involves multiple steps where a substrate is oxidized and a coenzyme is reduced. - Such a low number would fail to account for the multiple points of **NADH** and **FADH2** generation. *5* - This count is incorrect, as there are specifically four well-established dehydrogenase enzymes within the Krebs cycle responsible for the production of **NADH** or **FADH2**. - No additional dehydrogenase beyond the four listed plays a primary role in the canonical Krebs cycle.

Q: What is the primary role of molecular oxygen in the electron transport chain (ETC)?

Acting as the final electron acceptor. ***Acting as the final electron acceptor*** - **Molecular oxygen** is the terminal electron acceptor in the **electron transport chain**, combining with electrons and protons (H+) to form **water**. - Without oxygen, electron flow would cease, leading to a build-up of reduced electron carriers and halting ATP production via **oxidative phosphorylation**. *Transfer of electrons to CoQ* - **Coenzyme Q (CoQ)** accepts electrons from Complexes I and II but is an intermediate carrier, not the final destination. - The primary role of molecular oxygen occurs much later in the chain. *Transfer of electrons from cytosol to mitochondria* - This process involves specific shuttle systems (e.g., malate-aspartate, glycerol phosphate shuttle) but is distinct from oxygen's role within the ETC. - Oxygen's function is internal to the electron transport process in the mitochondrial matrix. *Facilitating ATP synthesis* - While oxygen's role as the final electron acceptor indirectly enables **ATP synthesis** by maintaining electron flow and the proton gradient, it does not directly synthesize ATP. - **ATP synthase** uses the proton gradient to produce ATP, a separate but dependent step.

Q: Which of the following metabolic processes is associated with increased Basal Metabolic Rate (BMR)?

Increased glycolysis. ***Increased glycolysis*** - Among the given options, **increased glycolysis** is the best answer as it represents **active catabolic metabolism** that generates ATP to meet energy demands. - While glycolysis itself doesn't directly increase BMR, **increased glycolytic activity occurs in metabolically active tissues** and reflects higher cellular energy turnover. - Tissues with higher metabolic rates (muscle, brain, liver) have increased glycolysis to meet their ATP demands, making this the most appropriate choice among the options provided. *Increased body fat store* - **Adipose tissue** is metabolically **less active** than lean tissue (muscle, organs). - Increased body fat typically results in a **lower BMR per unit body weight** because fat tissue has minimal metabolic activity compared to muscle. - Greater fat stores are associated with lower, not higher, metabolic rate. *Increased lipogenesis* - **Lipogenesis** (synthesis of fatty acids and triglycerides) is an **anabolic storage process**. - This process occurs during energy surplus and represents a state of **reduced energy expenditure** relative to energy intake. - Storage processes like lipogenesis are associated with **lower overall metabolic activity**, not increased BMR. *Increased glycogenesis* - **Glycogenesis** (synthesis of glycogen from glucose) is an **anabolic storage process** occurring primarily in liver and muscle. - This represents **energy storage**, not energy expenditure, and occurs during fed states when energy demands are being met. - Storage processes do not increase BMR; they indicate surplus energy being stored for later use.

Q: The electron transport chain is a series of redox reactions that result in ATP synthesis. Which of the following is a cytochrome complex IV inhibitor?

Cyanide. ***Cyanide*** - **Cyanide** is a potent inhibitor of **cytochrome c oxidase (Complex IV)** in the electron transport chain, binding to the ferric iron (Fe3+) in the heme group of the enzyme. - This binding prevents the transfer of electrons to **oxygen**, thereby halting cellular respiration and ATP production. *Carbon dioxide* - **Carbon dioxide** is a metabolic waste product and a component of the **bicarbonate buffer system**, but it does not directly inhibit cytochrome complex IV. - While high levels can affect physiological pH and enzyme function, its primary role is not as an electron transport chain inhibitor. *Oligomycin* - **Oligomycin** inhibits **ATP synthase (Complex V)** by binding to its Fo subunit, which blocks the flow of protons through the ATP synthase channel. - This prevents the synthesis of ATP but does not directly affect the electron transfer steps of cytochrome complex IV. *Ouabain* - **Ouabain** is a cardiac glycoside that inhibits the **Na+/K+-ATPase pump** in the cell membrane. - It does not have any direct inhibitory effect on the components of the electron transport chain, including cytochrome complex IV.

Q: In starvation, earliest to become depleted -

Carbohydrates. ***Carbohydrates*** - **Glycogen stores** (primarily liver and muscle glycogen) are the body's most readily accessible energy source and are depleted within hours of starvation. - The liver initially maintains blood glucose levels by breaking down **glycogen** before resorting to gluconeogenesis. *Proteins* - **Proteins** are conserved as much as possible during early starvation to preserve vital body functions. - Significant **protein breakdown** for energy (gluconeogenesis) typically occurs in later stages of prolonged starvation, after carbohydrate and most fat reserves are diminished. *Fats* - **Fats** (in the form of triglycerides stored in adipose tissue) become the primary energy source after glycogen stores are depleted. - While they provide a large energy reserve, their mobilization and utilization as fuel take longer than glycogen, and they are not the **earliest to be depleted**. *None of the options* - This option is incorrect because **carbohydrates** are indeed the earliest to be depleted during starvation.

Q: NADH CoQ reductase is inhibited by ?

Rotenone. ***Rotenone*** - **Rotenone** is a potent inhibitor of **NADH CoQ reductase**, also known as **Complex I** of the electron transport chain. - It blocks the transfer of electrons from **NADH** to **ubiquinone (CoQ)**, thereby halting oxidative phosphorylation. *Antimycin (inhibits cytochrome bc1 complex)* - **Antimycin A** specifically inhibits **Complex III (cytochrome bc1 complex)**, not **NADH CoQ reductase**. - Its action blocks electron transfer from **ubiquinol** to **cytochrome c**. *Atractyloside (inhibits ATP/ADP translocase)* - **Atractyloside** inhibits the **adenine nucleotide translocase (ATP/ADP translocase)**, which is responsible for exchanging ATP for ADP across the inner mitochondrial membrane. - It does not directly affect the electron transport chain components like **NADH CoQ reductase**. *Carbon monoxide (inhibits cytochrome c oxidase)* - **Carbon monoxide (CO)** is a classic inhibitor of **Complex IV (cytochrome c oxidase)**. - It binds to the **heme iron** of **cytochrome a3** with high affinity, preventing oxygen from acting as the final electron acceptor.

Q: Which of the following is not a cofactor required by pyruvate dehydrogenase?

Biotin. ***NAD*** - **NAD+ (Nicotinamide adenine dinucleotide)** is required by the dihydrolipoyl dehydrogenase (E3) component of the pyruvate dehydrogenase complex to accept electrons and form NADH. - This cofactor is crucial for the regeneration of the oxidized lipoamide, allowing the complex to continue its catalytic cycle. *FAD* - **FAD (Flavin adenine dinucleotide)** is also a cofactor for the dihydrolipoyl dehydrogenase (E3) enzyme, accepting electrons from reduced lipoamide before transferring them to NAD+. - It is tightly bound to the E3 enzyme and undergoes reversible oxidation-reduction during the reaction. *Biotin* - **Biotin** is primarily a cofactor for **carboxylase enzymes**, such as pyruvate carboxylase, which catalyzes the conversion of pyruvate to oxaloacetate. - It is **not involved** in the pyruvate dehydrogenase complex reaction, which is an oxidative decarboxylation, not a carboxylation. *CoA* - **Coenzyme A (CoA)** is essential for the pyruvate dehydrogenase complex, as it accepts the acetyl group from pyruvate to form **acetyl-CoA**. - Acetyl-CoA is the product of the reaction and serves as the entry molecule into the **Krebs cycle**.

Question 1

Sequence of complexes in the electron transport chain is -

Accepted Answer

NADH dehydrogenase → Q → Cytochrome bc1 → Cytochrome aa3 → O2

Answer

NADH dehydrogenase → Cytochrome aa3 → Q → Cytochrome bc1 → O2

Answer

NADH dehydrogenase → Q → Cytochrome aa3 → Cytochrome bc1 → O2

Answer

NADH dehydrogenase → Cytochrome bc1 → Q → Cytochrome aa3 → O2

Question 2

Cancer cells preferentially utilize glycolysis for energy production even in the presence of adequate oxygen. What is this phenomenon called?

Accepted Answer

Warburg effect

Answer

Hypoxic adaptation

Answer

Anoxic survival

Answer

Oxygen-independent metabolism

Question 3

What is the total number of dehydrogenases involved in the Krebs cycle?

Accepted Answer

4

Answer

3

Answer

2

Answer

5

Question 4

What is the primary role of molecular oxygen in the electron transport chain (ETC)?

Accepted Answer

Acting as the final electron acceptor

Answer

Transfer of electrons to CoQ

Answer

Transfer of electrons from cytosol to mitochondria

Answer

Facilitating ATP synthesis

Question 5

Which of the following metabolic processes is associated with increased Basal Metabolic Rate (BMR)?

Accepted Answer

Increased glycolysis

Answer

Increased body fat store

Answer

Increased lipogenesis

Answer

Increased glycogenesis

Question 6

The electron transport chain is a series of redox reactions that result in ATP synthesis. Which of the following is a cytochrome complex IV inhibitor?

Accepted Answer

Cyanide

Answer

Carbon dioxide

Answer

Oligomycin

Answer

Ouabain

Question 7

Which of the following statements best describes the role of inorganic phosphate in the Electron Transport Chain (ETC)?

Accepted Answer

Inorganic phosphate is essential for ATP synthesis in the ETC.

Answer

Generates ATP

Answer

Occurs in mitochondria

Answer

No role of inorganic phosphate

Question 8

In starvation, earliest to become depleted -

Accepted Answer

Carbohydrates

Answer

Proteins

Answer

Fats

Answer

None of the options

Question 9

NADH CoQ reductase is inhibited by ?

Accepted Answer

Rotenone

Answer

Antimycin (inhibits cytochrome bc1 complex)

Answer

Atractyloside (inhibits ATP/ADP translocase)

Answer

Carbon monoxide (inhibits cytochrome c oxidase)

Question 10

Which of the following is not a cofactor required by pyruvate dehydrogenase?

Accepted Answer

Biotin

Answer

CoA

Answer

NAD

Answer

FAD

Energy Production and Metabolism — MCQs

Energy Production and Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?