Stages of Energy Generation from Food Oxidation

Energy Generation from Food Oxidation

• Energy from food is generated through three stages: digestion, metabolism, and oxidative phosphorylation.
• Digestion breaks down large food molecules into smaller units.
• Small molecules are further degraded to form acetyl CoA, producing some ATP.
• Complete oxidation of acetyl CoA occurs in the Citric Acid Cycle (Krebs Cycle), generating carbon dioxide and ATP.

Importance of Continuous Energy Input

• Continuous energy is essential for:
  • Performing mechanical work.
  • Active transport of molecules and ions.
  • Synthesizing macromolecules from smaller precursors.

Sources of Energy

• Phototrophs harness energy from sunlight through photosynthesis.
• Chemotrophs obtain energy by oxidizing carbon compounds.

Metabolic Pathways

• Metabolism consists of interconnected chemical reactions that convert biomolecules efficiently, avoiding harmful byproducts.
• Metabolic pathways can be categorized as:
  • Catabolism: Breaks down fuel molecules to generate ATP or ion gradients.
  • Anabolism: Requires energy input for the synthesis of molecules like glucose, fats, or DNA.

Amphibolic Pathways

• Amphibolic pathways can function as either anabolic or catabolic based on the cell's energy state.
• Each pathway has unique regulated or irreversible reactions.

Criteria for Metabolic Pathways

• Specific individual reactions yield definite products.
• The collective reactions of a pathway must be thermodynamically favorable.

Free Energy Changes

• Overall free energy change of a series of reactions equals the sum of individual free-energy changes.
• Unfavorable reactions can occur when coupled with favorable ones, maintaining a negative overall free energy.

Redox Reactions in Metabolism

• Oxidation of carbon fuels to carbon dioxide is paired with reduction reactions to regenerate ATP from ADP and inorganic phosphate (Pi).
• Oxidation: Loss of electrons.
• Reduction: Gain of electrons.
• Molecular oxygen is the final electron acceptor in carbon oxidation.

Substrate-Level Phosphorylation

• ATP acts as an activated carrier of phosphoryl groups, facilitating thermodynamically unfavorable reactions.
• Transfer of phosphoryl groups is exergonic, influencing protein energy and activity.

Activated Carriers of Electrons

• Nicotinamide adenine dinucleotide (NAD+):

  • Derived from niacin.
  • Accepts two electrons and a hydrogen ion, forming NADH.

• Flavin adenine dinucleotide (FAD):

  • Derived from riboflavin.
  • Accepts two electrons and protons, forming FADH2.

Role of NADPH

• NADPH serves as an electron donor in reductive biosynthesis.
• Distinct from NADH due to a 2’-hydroxyl group esterified with phosphate, enhancing recognition by enzymes.

Coenzyme A (CoA)

• CoA is an important carrier of acyl groups used in both catabolic and anabolic processes.
• Acyl groups bind to the terminal sulfhydryl group of CoA, forming acetyl CoA.
• The transfer of acetyl groups is energetically favorable.

Regulation of Metabolism

• Enzyme control is essential for maintaining homeostasis and regulating metabolism.
• Regulation occurs through:
  • Control of enzyme amounts via gene transcription and degradation.
  • Catalytic activity modification via allosteric control or reversible covalent modifications.

Learn about the three stages involved in the generation of energy from the oxidation of food, including digestion, conversion to acetyl CoA, and the production of ATP through the Citric Acid Cycle and oxidative phosphorylation.