Short Questions and answers of Metabolism of Biomolecules
Topic - Carbohydrate metabolism : Glycolysis and its regulation
1. What is glycolysis?
Answer: Glycolysis is a fundamental metabolic pathway in which glucose is broken down into two molecules of pyruvate, generating ATP and NADH in the process.
2. Where does glycolysis take place in the cell.
Answer: Glycolysis occurs in the cytoplasm of the cell.
3. What are the main substrates and products of glycolysis?
Answer: The substrates of glycolysis are glucose, and the products are two molecules of pyruvate, two molecules of NADH, and a net gain of two ATP molecules.
4. What is the role of ATP in glycolysis?
Answer: ATP is both consumed and generated in glycolysis. Two ATP molecules are used in the early steps of glycolysis, and four ATP molecules are produced, resulting in a net gain of two ATP molecules.
5. What is the significance of NADH in glycolysis?
Answer :NADH is an important coenzyme that carries high-energy electrons. It is generated in glycolysis and plays a crucial role in the electron transport chain during oxidative phosphorylation, where it contributes to the production of ATP.
6. How is glycolysis regulated?
Answer: Glycolysis is regulated at key steps to maintain energy balance in the cell. It is primarily regulated by feedback mechanisms and allosteric regulation. Some key regulatory points include the enzymes phosphofructokinase and pyruvate kinase, which are inhibited by ATP and stimulated by ADP and AMP.
7. What is the role of hexokinase in glycolysis?
Answer: Hexokinase is the enzyme responsible for the first step of glycolysis, where it phosphorylates glucose to form glucose-6-phosphate. This step requires ATP, and it traps glucose within the cell, as glucose-6-phosphate cannot easily exit the cell membrane.
8. Why is the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate a key regulatory step in glycolysis?
Answer: This conversion is catalyzed by the enzyme phosphofructokinase-1 (PFK-1) and is a highly regulated step in glycolysis. It is an important control point because it commits the cell to glycolysis and is inhibited by high levels of ATP and citrate, signaling that the cell has sufficient energy.
9. What happens to pyruvate produced in glycolysis under aerobic and anaerobic conditions?
Answer: Under aerobic conditions, pyruvate is transported into the mitochondria and enters the citric acid cycle (Krebs cycle) for further energy extraction. Under anaerobic conditions, pyruvate may be converted to lactate in some cells (lactic acid fermentation) or to ethanol and carbon dioxide in yeast and some bacteria (alcoholic fermentation).
10. What is the overall importance of glycolysis in metabolism?
Answer: Glycolysis is a central metabolic pathway that provides the cell with ATP and metabolic intermediates for various biosynthetic processes. It is the starting point for glucose catabolism and is essential for energy production in both aerobic and anaerobic conditions.
Topic- Gluconeogenesis, Glycogenolysis TCA cycle
Gluconeogenesis:
1. What is gluconeogenesis, and why is it important in carbohydrate metabolism?
- Gluconeogenesis is a metabolic pathway that synthesizes glucose from non-carbohydrate precursors, primarily amino acids and glycerol.
- It is crucial because it ensures a steady supply of glucose for the body, especially during fasting or low-carbohydrate conditions.
2. Where does gluconeogenesis primarily occur in the body?
- Gluconeogenesis mainly occurs in the liver and, to a lesser extent, in the kidneys.
3. What are the key substrates used in gluconeogenesis?
- Key substrates include lactate, amino acids (such as alanine), glycerol, and certain intermediates from the citric acid cycle (TCA cycle).
4. Explain the regulatory mechanisms of gluconeogenesis.
- Hormones like glucagon and cortisol stimulate gluconeogenesis, while insulin inhibits it. -These hormones act through intracellular signaling pathways to regulate the activity of key enzymes involved in gluconeogenesis.
Glycogenolysis:
5. What is glycogenolysis, and how does it relate to glycogen?
- Glycogenolysis is the breakdown of glycogen, a branched polymer of glucose, into individual glucose molecules. This process releases glucose to maintain blood sugar levels.
6. Where does glycogenolysis occur, and why is it essential?
- Glycogenolysis mainly occurs in the liver and muscle cells. It is essential for providing a rapid source of glucose when the body's energy demands increase, such as during exercise.
7. What triggers the activation of glycogenolysis?
- Hormones such as epinephrine (adrenaline) and glucagon activate glycogenolysis in response to the body's need for energy.
TCA Cycle (Citric Acid Cycle):
8. What is the TCA cycle, and where does it take place in the cell?
- The TCA cycle is a central metabolic pathway that occurs in the mitochondria.
- It plays a crucial role in the oxidative metabolism of various organic compounds, including carbohydrates, fats, and amino acids.
9. What are the main products and intermediates of the TCA cycle?
- The main products are ATP, NADH, FADH2, and carbon dioxide (CO2). Key intermediates include citrate, isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, and malate.
10. How does the TCA cycle connect to other metabolic pathways, like glycolysis and fatty acid oxidation?
- The TCA cycle is at the crossroads of carbohydrate, fatty acid, and amino acid metabolism. Various molecules from these pathways feed into the TCA cycle, and its intermediates can be used as precursors for biosynthesis or energy production.
11. What is the role of oxygen in the TCA cycle?
- Oxygen is the final electron acceptor in the electron transport chain, which is closely linked to the TCA cycle. The TCA cycle generates NADH and FADH2, which are used in the electron transport chain to produce ATP when oxygen is available.
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