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 Gibbs free energy (ΔG) of a reaction, they lower the activation energy
• A spontaneous reaction has a negative ΔG (exergonic), meaning it releases energy.
• A non-spontaneous reaction has a positive ΔG (endergonic), meaning it requires energy input.
• ATP (adenosine triphosphate) is a high-energy molecule that stores and releases energy for cellular processes.
• ATP provides energy for various cellular processes through the breakdown of its phosphate bonds.
• Different types of reactions can be coupled to facilitate unfavorable reactions.

ATP Production

• Substrate-level phosphorylation is a metabolic reaction that results in the formation of ATP. It occurs during glycolysis.
• Oxidative phosphorylation is a metabolic pathway that produces ATP through the oxidation of NADH and FADH2. It involves the electron transport chain (ETC).

Carbohydrate Metabolism

• Glycolysis is the metabolic pathway that breaks down glucose into pyruvate.
• Glycolysis produces ATP and NADH as energy carriers.
• Glycolysis produces intermediates that can be used in other metabolic pathways.
• Glycolysis takes place in the cytoplasm of the cell.
• Glycolysis takes place in two separate stages: the investment phase and the harvest phase.
• Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate precursors.
• There are three regulated steps in Glycolysis and they are often regulated in response to hormonal cues.

TCA Cycle

• The citric acid cycle, also called the tricarboxylic acid cycle or the Krebs cycle, is a central metabolic pathway for the oxidation of Acetyl-CoA.
• The TCA cycle is localized in the mitochondrial matrix.
• The TCA cycle generates high-energy electrons (NADH and FADH2) and CO2.
• Pyruvate is transported from the cytoplasm to the matrix in the mitochondria.
• The TCA cycle happens inside the mitochondria.

Oxidative Phosphorylation and ETC

• Electrons from NADH and FADH2 are transported through a series of protein complexes called the electron transport chain (ETC).
• The flow of electrons through the ETC creates a proton gradient across the inner mitochondrial membrane.
• ATP is synthesized by ATP synthase using the energy from the proton gradient.
• NADH produces more ATP than FADH2.

Pentose Phosphate Pathway

• The pentose phosphate pathway is an alternative pathway for glucose metabolism.
• This pathway produces NADPH, a reducing agent required in various biosynthetic reactions.
• This pathway produces Ribose 5 Phosphate, a precursor for nucleotide synthesis.
• This pathway has two phases. The oxidative phase and the non-oxidative phase.

Glycogen

• Glycogen is a storage form of glucose in animals.
• Glycogen is primarily stored in the liver and muscles.
• Glycogen synthesis and degradation are regulated processes.

Glycogen Metabolism

• Glycogen synthesis involves the activation of glucose and its incorporation into a glycogen molecule
• Glycogen degradation involves the cleavage of glucose from the end of a glycogen chain

Hormonal Regulation of Glycolysis

• Hormones like insulin and glucagon regulate glycolytic activity depending on the body needs.

Transfer of Cytoplasmic NADH to Mitochondria

• Cytoplasmic NADH cannot directly enter the mitochondria and must use a shuttle system.
• Two common shuttle mechanisms are the malate-aspartate shuttle and the glycerol 3-phosphate shuttle.