1. Define metabolic pathways. What are anabolic and catabolic reactions?
Answer:
Metabolic Pathways:
Metabolic pathways are a series of interconnected biochemical reactions that occur within a cell to sustain life. These pathways are responsible for the transformation of molecules to maintain cellular functions, growth, and reproduction.
Anabolic Reactions:
Anabolic reactions involve the synthesis of complex molecules from simpler ones, requiring an input of energy, typically in the form of ATP. Examples include protein synthesis, DNA replication, and photosynthesis.
Catabolic Reactions:
Catabolic reactions break down complex molecules into simpler ones, releasing energy that is often captured as ATP. Examples include glycolysis, beta-oxidation of fatty acids, and cellular respiration.
2. Compare anabolic and catabolic reactions with examples.
Answer:
| Feature | Anabolic Reactions | Catabolic Reactions |
|---|---|---|
| Function | Builds complex molecules | Breaks down complex molecules |
| Energy Usage | Consumes energy (endergonic) | Releases energy (exergonic) |
| Examples | Protein synthesis, Photosynthesis | Glycolysis, Cellular respiration |
| Purpose | Growth, repair, storage of energy | Energy production, resource mobilization |
3. What is the significance of ATP in anabolic and catabolic pathways?
Answer:
ATP (adenosine triphosphate) is the energy currency of the cell:
- In Anabolic Reactions: ATP provides the energy needed for synthesizing complex molecules, such as proteins, nucleic acids, and lipids.
- In Catabolic Reactions: ATP is generated by breaking down molecules like glucose and fatty acids. This energy is then utilized by anabolic pathways and other cellular processes.
4. Explain the concept of energy coupling in metabolic pathways.
Answer:
Energy coupling is the process by which energy released from catabolic reactions is used to drive anabolic reactions. For instance, the energy from ATP hydrolysis (a catabolic process) powers biosynthesis (an anabolic process). This interdependence ensures efficient energy utilization within cells.
5. Describe the role of enzymes in metabolic pathways.
Answer:
Enzymes act as biological catalysts in metabolic pathways. They:
- Lower the activation energy required for reactions.
- Ensure specificity, allowing only the desired reaction to occur.
- Facilitate the regulation of metabolic pathways via feedback inhibition and activation.
For example, hexokinase catalyzes the first step of glycolysis, ensuring glucose is efficiently converted into glucose-6-phosphate.
6. What is the importance of cofactors and coenzymes in metabolic reactions?
Answer:
Cofactors (metal ions like Mg²⁺) and coenzymes (organic molecules like NAD⁺ and FAD) assist enzymes by:
- Stabilizing enzyme-substrate complexes.
- Accepting or donating electrons or chemical groups.
For instance, NAD⁺ is reduced to NADH in glycolysis, acting as an electron carrier in subsequent pathways.
7. How is glycolysis an example of a catabolic pathway?
Answer:
Glycolysis is a catabolic pathway where one glucose molecule (6-carbon) is broken down into two molecules of pyruvate (3-carbon), generating:
- ATP: Two net molecules of ATP per glucose.
- NADH: Two molecules, which are used in the electron transport chain for further ATP synthesis.
8. Discuss the role of photosynthesis in anabolic pathways.
Answer:
Photosynthesis is an anabolic process where light energy is used to synthesize glucose from carbon dioxide and water. It consists of:
- Light-dependent reactions: Generate ATP and NADPH.
- Calvin Cycle: Uses ATP and NADPH to produce glucose, which is stored for energy.
9. Explain the beta-oxidation pathway as a catabolic process.
Answer:
Beta-oxidation is the catabolic process by which fatty acids are broken down in the mitochondria to produce acetyl-CoA. This acetyl-CoA enters the citric acid cycle, contributing to the production of ATP, NADH, and FADH₂.
10. What is the role of the urea cycle in metabolism?
Answer:
The urea cycle detoxifies ammonia, a byproduct of protein catabolism, by converting it into urea for excretion. This process is crucial for maintaining nitrogen balance and preventing ammonia toxicity.
11. Describe the importance of the citric acid cycle in catabolism.
Answer:
The citric acid cycle (Krebs cycle) oxidizes acetyl-CoA to CO₂, generating high-energy molecules:
- NADH and FADH₂ for ATP synthesis in the electron transport chain.
- ATP directly through substrate-level phosphorylation.
12. How does gluconeogenesis complement catabolism?
Answer:
Gluconeogenesis is an anabolic pathway that synthesizes glucose from non-carbohydrate precursors, such as lactate and amino acids. It replenishes glucose levels during fasting, ensuring a steady energy supply.
13. What is the significance of feedback inhibition in metabolic regulation?
Answer:
Feedback inhibition prevents overproduction by using the end product of a pathway to inhibit a key enzyme early in the process. For example, ATP inhibits phosphofructokinase during glycolysis.
14. How do anabolic and catabolic pathways contribute to homeostasis?
Answer:
Anabolic and catabolic pathways maintain cellular energy balance:
- Anabolism stores energy and builds necessary molecules.
- Catabolism releases energy when needed.
Together, they adapt to changing energy demands.
15. Explain oxidative phosphorylation as a catabolic process.
Answer:
Oxidative phosphorylation occurs in the mitochondria, where electrons from NADH and FADH₂ are passed through the electron transport chain, generating a proton gradient that drives ATP synthesis.
16. Compare the metabolic fates of carbohydrates, proteins, and fats.
Answer:
- Carbohydrates: Broken down into glucose → Glycolysis → ATP.
- Proteins: Degraded into amino acids → Deaminated → Enter pathways as intermediates.
- Fats: Hydrolyzed into glycerol and fatty acids → Glycerol enters glycolysis, fatty acids undergo beta-oxidation.
17. What role does NADH play in metabolism?
Answer:
NADH acts as an electron carrier, transferring electrons to the electron transport chain during catabolic pathways, ultimately generating ATP.
18. Describe the interconnection between anabolic and catabolic pathways in the liver.
Answer:
The liver integrates metabolism:
- Converts glucose into glycogen (anabolism).
- Breaks down glycogen to glucose during fasting (catabolism).
- Synthesizes fatty acids and metabolizes them for energy as needed.
19. How do hormones regulate metabolic pathways?
Answer:
Hormones like insulin and glucagon regulate metabolism:
- Insulin: Promotes anabolic pathways (glycogenesis, protein synthesis).
- Glucagon: Activates catabolic pathways (glycogenolysis, gluconeogenesis).
20. What is the role of AMP-activated protein kinase (AMPK) in metabolism?
Answer:
AMPK is a cellular energy sensor:
- Activates catabolic pathways to generate ATP.
- Inhibits anabolic pathways to conserve energy.
