Bioenergetics and ATP Production

Bioenergetics

• Bioenergetics is the transfer and utilization of energy in biological systems.
• Bioenergetics predicts if a process is possible, while kinetics measures the reaction rate.
• Enzymes do not change the overall change in energy (ΔG).

Free Energy

• Free energy (G) is useful for determining if a reaction will occur spontaneously.
• A negative ΔG indicates a spontaneous reaction, releasing energy (exergonic).
• A positive ΔG indicates a nonspontaneous reaction, requiring energy input (endergonic).
• Energy difference (ΔG): (Final E) - (Initial E)

ATP Production

• Substrate-level phosphorylation is a direct method of ATP production during a metabolic reaction.
• Oxidative phosphorylation is a process that involves the electron transport chain and chemiosmosis, resulting in the formation of ATP.
• ADP is converted to ATP in both substrate-level phosphorylation and oxidative phosphorylation.

Carbohydrate Metabolism

• Carbohydrates are a primary source of energy for the body.
• Glycolysis is the breakdown of glucose into pyruvate in the cytoplasm.
• Glycogen is a storage form of glucose primarily in muscle and liver.
• Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources.

Glycolysis

• Glycolysis produces ATP directly, NADH (electron carrier).
• Glycolysis provides intermediates for other metabolic pathways.
• Three rate-limiting and regulation steps are involved in glycolysis, to stop or start it based on the need of the cell.

TCA Cycle

• Citrate Cycle (CAC), Tricarboxylic acid (TCA) Cycle, Krebs Cycle are all terms for the same process.
• Pyruvate should be transported to mitochondria for the citric acid cycle process
• It's the link between the end products of glycolysis and further oxidation in the mitochondria.

Oxidative Phosphorylation and ETC

• The Electron Transport Chain (ETC) is a series of protein complexes that use energy from NADH and FADH2 to pump H⁺ (protons) across the inner mitochondrial membrane.
• Electrons are carried from NADH and FADH2 through ETC to cause a proton gradient (flow). ATP is synthesized by using energy of this flow.

Pentose Phosphate Pathway

• Provides important molecules like NADPH and Ribose-5-phosphate.
• It involves both oxidative (irreversible) and non-oxidative (reversible) reactions.
• Ribose 5-P : Nucleotide and Nucleic acid synthesis, and glycolysis intermediates.
• It produces important molecules and is crucial for cell operation.

Glycogen

• Glycogen is a storage form of glucose stored in muscle and liver.
• Glycogenolysis is the breakdown of glycogen to release glucose.
• Glycogenesis is the synthesis of glycogen from glucose.
• Glycogen plays an important role in maintaining glucose levels in the blood.

Gluconeogenesis

• Gluconeogenesis is the process of synthesizing new glucose from non-carbohydrate sources.
• It uses different enzymes and steps compared to glycolysis (opposite path to glycolysis in some places).
• Main differences are enzymes like PEP carboxykinase, and in some steps gluconeogenesis doesn't use the same enzymes.
• Important for maintaining blood glucose levels when other sources are unavailable.

Transfer of Cytoplasmic NADH to Mitochondria

• Two shuttles (Malate-Aspartate and Glycerol 3-phosphate) facilitate the transfer of electrons from cytoplasmic NADH to mitochondrial NAD⁺.
• Key difference between the two shuttles concerns the final electron acceptor (NAD⁺ or FAD⁺). In terms of the net gain of ATP from cytoplasmic NADH, the Malate-Aspartate shuttle produces more ATP than the Glycerol 3-phosphate shuttle.