Energy Production and Metabolism

Energy Production and Metabolism Indian Medical PG Question 1: Organ that can utilize glucose, fatty acids and ketone bodies is:

• A. Liver
• B. Brain
• C. Skeletal muscle (Correct Answer)
• D. RBC

Energy Production and Metabolism Explanation: ***Skeletal muscle*** - Skeletal muscle is highly adaptable and can utilize **glucose**, **fatty acids (FAs)**, and **ketone bodies** as fuel sources, especially during prolonged exercise or starvation. - Its metabolic flexibility allows it to switch between these substrates depending on their availability and the body's energy demands. *Liver* - The liver is central to metabolism but primarily **produces ketone bodies** from fatty acids rather than utilizing them as a major fuel source for its own energy needs. - While it uses glucose and FAs, its role in ketone body metabolism is largely synthetic. *Brain* - The brain preferentially uses **glucose** as its primary fuel. - During prolonged starvation, it can adapt to utilize **ketone bodies** as an alternative fuel source, but it does not significantly use fatty acids directly. *RBC* - Red blood cells (RBCs) lack mitochondria and therefore rely exclusively on **anaerobic glycolysis** for energy, metabolizing only **glucose**. - They cannot utilize fatty acids or ketone bodies.

Energy Production and Metabolism Indian Medical PG Question 2: Which of the following enzymes is not targeted by hypolipidemic drugs?

• A. HMG Co A reductase
• B. Lipoprotein lipase
• C. Acyl CoA, cholesterol acyl transferase 1
• D. Peripheral decarboxylase (Correct Answer)

Energy Production and Metabolism Explanation: ***Peripheral decarboxylase*** - **Peripheral decarboxylase** (also known as DOPA decarboxylase) is involved in the synthesis of dopamine from L-DOPA and is a target for drugs used in **Parkinson's disease**, not hypolipidemic drugs. - Its inhibition by drugs like **carbidopa** or **benserazide** prevents the peripheral conversion of L-DOPA to dopamine, increasing L-DOPA availability for the brain. *HMG Co A reductase* - **HMG-CoA reductase** is the rate-limiting enzyme in cholesterol biosynthesis and is the primary target for **statins** (e.g., atorvastatin, simvastatin). - Statins effectively lower **LDL cholesterol** by inhibiting this enzyme, reducing endogenous cholesterol production. *Lipoprotein lipase* - **Lipoprotein lipase (LPL)** activity can be enhanced by certain hypolipidemic drugs, such as **fibrates**, which activate **PPAR-α**. - Increased LPL activity leads to enhanced hydrolysis of **triglycerides** from VLDL and chylomicrons, reducing triglyceride levels in plasma. *Acyl CoA, cholesterol acyl transferase 1* - **Acyl-CoA:cholesterol acyltransferase (ACAT) inhibitors** were developed as potential hypolipidemic agents to prevent cholesterol esterification and absorption. - While not widely used clinically due to efficacy and side effect profiles, **ACAT1** is involved in cholesterol esterification in the intestine and liver, making it a target for reducing cholesterol absorption.

Energy Production and Metabolism Indian Medical PG Question 3: 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?

• A. Cyanide (Correct Answer)
• B. Carbon dioxide
• C. Oligomycin
• D. Ouabain

Energy Production and Metabolism Explanation: ***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.

Energy Production and Metabolism Indian Medical PG Question 4: Which of the following processes does not occur in mitochondria?

• A. Fatty acid oxidation
• B. Electron transport chain
• C. Glycogenolysis (Correct Answer)
• D. Citric acid cycle (Kreb's cycle)

Energy Production and Metabolism Explanation: ***Glycogenolysis*** - **Glycogenolysis** is the breakdown of **glycogen** into glucose, which primarily occurs in the **cytosol** of cells, mainly in the liver and muscles. - This process is crucial for maintaining blood glucose levels and providing energy during periods of fasting or increased demand, and it does not take place within the mitochondria. *Fatty acid oxidation* - **Fatty acid oxidation**, also known as beta-oxidation, is a mitochondrial process that breaks down fatty acids into **acetyl-CoA** for energy production. - This occurs extensively within the mitochondrial matrix, producing ATP. *Electron transport chain* - The **electron transport chain** is located in the **inner mitochondrial membrane** and is the final stage of aerobic respiration, producing the majority of ATP. - It involves a series of protein complexes that transfer electrons to oxygen, creating a proton gradient for ATP synthesis. *Citric acid cycle (Kreb's cycle)* - The **citric acid cycle**, or **Krebs cycle**, is a central metabolic pathway that occurs in the **mitochondrial matrix**. - It oxidizes acetyl-CoA, derived from carbohydrates, fats, and proteins, to produce ATP, NADH, and FADH2.

Energy Production and Metabolism Indian Medical PG Question 5: Enzyme activated by decrease in Insulin: glucagon ratio:

• A. PFK
• B. Glucose 6 phosphatase (Correct Answer)
• C. Glucokinase
• D. Hexokinase

Energy Production and Metabolism Explanation: ***Glucose 6 phosphatase*** - A decreased **insulin:glucagon ratio** signifies a catabolic state, promoting glucose release into the blood. - **Glucose-6-phosphatase** is the key enzyme in **gluconeogenesis** and **glycogenolysis** in the liver, dephosphorylating **glucose-6-phosphate** to **free glucose**, which can then be exported from the liver. *PFK* - **Phosphofructokinase (PFK)** is a key regulatory enzyme in **glycolysis**, which is inhibited in a state of low insulin:glucagon ratio. - Its activity would decrease, not increase, to reduce glucose utilization. *Glucokinase* - **Glucokinase** phosphorylates glucose to **glucose-6-phosphate** in the liver, trapping it for metabolism; its activity is increased by high insulin levels. - In a low insulin:glucagon ratio, its activity would be reduced to conserve glucose. *Hexokinase* - **Hexokinase** phosphorylates glucose in most peripheral tissues but has a lower Km for glucose than glucokinase, becoming saturated even at low glucose concentrations. - Its activity is not primarily regulated by the insulin:glucagon ratio; it is generally involved in glucose uptake for cellular energy needs.

Energy Production and Metabolism Flashcard 1 of 5

Question: _____ is an inhibitor of ATP synthase of the ETC

Answer: Oligomycin

Energy Production and Metabolism Flashcard 2 of 5

Question: When insulin acts on muscle tissue, it causes _____ glycogen storage and increased protein synthesis

Answer: increased

Energy Production and Metabolism Flashcard 3 of 5

Question: Aerobic metabolism of glucose produces _____ net ATP via the glycerol-3-phosphate shuttle (muscle)

Answer: 30

Energy Production and Metabolism Flashcard 4 of 5

Question: Pyruvate dehydrogenase is regulated via positive feedback by _____, Ca2+, and increased NAD+/NADH ratio

Answer: ADP

Energy Production and Metabolism Flashcard 5 of 5

Question: Lactic acidosis type _____ is due to anaerobic metabolism secondary to poor tissue perfusion.

Answer: A