Energy Production and Metabolism Practice Questions

Q: Which of the following is not used in the citric acid cycle?

NADP. ***NADP*** - **NADP (nicotinamide adenine dinucleotide phosphate)** is primarily involved in anabolic reactions, such as fatty acid synthesis and the **pentose phosphate pathway**. - It is not a direct coenzyme or substrate involved in the oxidative reactions of the **citric acid cycle**. *NAD* - **NAD (nicotinamide adenine dinucleotide)** is a crucial coenzyme in the citric acid cycle, acting as an electron acceptor in several steps. - It is reduced to **NADH**, which then donates electrons to the electron transport chain for ATP production. *FAD* - **FAD (flavin adenine dinucleotide)** is another essential coenzyme in the citric acid cycle, reduced to **FADH2**. - **FADH2** transports electrons to the electron transport chain, contributing to ATP generation. *GDP* - **GDP (guanosine diphosphate)** is converted to **GTP (guanosine triphosphate)** in a substrate-level phosphorylation step during the conversion of succinyl-CoA to succinate in the citric acid cycle. - While not directly involved as an electron carrier, its phosphorylation is a key energy-generating step within the cycle.

Q: Which of the following organelles is primarily responsible for cellular respiration?

Mitochondria. ***Mitochondria*** - This organelle is often referred to as the "**powerhouse of the cell**" because it is the primary site of **ATP synthesis** through aerobic respiration. - Cellular respiration involves a series of metabolic reactions that convert nutrients into **adenosine triphosphate (ATP)**, providing energy for cellular functions. *Endoplasmic Reticulum* - The **endoplasmic reticulum** is primarily involved in **protein synthesis** (rough ER) and **lipid synthesis** and detoxification (smooth ER). - It does not play a direct role in the production of bulk cellular energy via cellular respiration. *Lysosome* - **Lysosomes** are responsible for **waste breakdown**, recycling cellular debris, and degrading foreign substances through their digestive enzymes. - They are not involved in the processes of cellular respiration or energy production. *Nucleus* - The **nucleus** contains the cell's **genetic material** (DNA) and controls cell growth, metabolism, and reproduction by regulating gene expression. - While it controls cellular processes, it does not directly perform cellular respiration.

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: Which of the following primarily occurs in the mitochondria?

ETC. ***Correct Option: ETC*** - The **electron transport chain (ETC)** is a series of protein complexes located **exclusively in the inner mitochondrial membrane**. - It occurs **solely in mitochondria** with no cytosolic component, making it the process that most "primarily" occurs in this organelle. - Its primary role is to generate a **proton gradient** through electron transfer, ultimately producing ATP via **oxidative phosphorylation**. - This is the definitive mitochondrial process among the options. *Ketogenesis* - **Ketogenesis** does occur entirely in the **mitochondrial matrix** of liver cells during fasting or low carbohydrate intake. - While mitochondrial, it is tissue-specific (primarily liver) and metabolically conditional (occurs during fasting states). - It involves synthesis of **ketone bodies** (acetoacetate, β-hydroxybutyrate) from acetyl-CoA. *Urea cycle* - The **urea cycle** is compartmentalized between the **mitochondrial matrix** and **cytosol** of liver cells. - First two steps (carbamoyl phosphate synthetase I and ornithine transcarbamylase) occur in mitochondria. - Remaining steps occur in cytosol, so it is NOT primarily mitochondrial. - Functions to detoxify **ammonia** by converting it to urea. *Steroid synthesis* - **Steroid synthesis** primarily occurs in the **smooth endoplasmic reticulum**. - Only specific steps (e.g., cholesterol side-chain cleavage by CYP11A1) occur in mitochondria. - Most of the steroidogenic pathway is extra-mitochondrial.

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: 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.

Question 1

Which of the following is not used in the citric acid cycle?

Accepted Answer

NADP

Answer

NAD

Answer

FAD

Answer

GDP

Question 2

Which of the following statements about the electron transport chain is false?

Accepted Answer

Complexes are arranged in a decreasing order of redox potential

Answer

6 Hydrogen ions are translocated when FADH2 electrons get into electron transport chain.

Answer

Mitochondrial Glycerol phosphate dehydrogenase sends its electron directly to Q

Answer

10 Hydrogen ions are translocated when NADH enters into an electron transport chain

Question 3

Which of the following organelles is primarily responsible for cellular respiration?

Accepted Answer

Mitochondria

Answer

Endoplasmic Reticulum

Answer

Lysosome

Answer

Nucleus

Question 4

Regarding energy production by the electron transport chain, which is true?

Accepted Answer

The complexes are arranged in an increasing order of redox potential

Answer

The complexes are arranged in an increasing order of energy level

Answer

The complexes are arranged in an increasing order of ability to accept electrons

Answer

The complexes are arranged in an increasing order of oxidation state

Question 5

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 6

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 7

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 8

Which of the following primarily occurs in the mitochondria?

Accepted Answer

ETC

Answer

Ketogenesis

Answer

Urea cycle

Answer

Steroid synthesis

Question 9

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 10

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)

Energy Production and Metabolism — MCQs

Energy Production and Metabolism — MCQs

On this page

Practice by Chapter

Want unlimited practice?