Cellular respiration and fermentation are fundamental processes allowing organisms to utilize the energy stored in biological macromolecules. Prokaryotes carry out cellular respiration within the cytoplasm or on the inner surface of the cell, while eukaryotes perform cellular respiration in the mitochondria. This process involves a series of coordinated enzyme-catalyzed reactions that capture energy from biological macromolecules. Cellular respiration is a catabolic pathway that breaks down organic molecules and uses an electron transport chain for ATP production.
Glycolysis and Substrate-Level Phosphorylation
Glycolysis is a biochemical pathway that releases energy in glucose to form ATP from ADP and inorganic phosphate, NADH from NAD+, and pyruvate. It takes place in the cytoplasm of the cell and involves the splitting of glucose into pyruvate. Substrate-level phosphorylation, which refers to the substrate molecule being an organic molecule that is an intermediate during the breakdown of glucose, occurs during glycolysis and the Krebs cycle, producing small amounts of ATP.
The Krebs Cycle
In the Krebs cycle, carbon dioxide is released from organic intermediates, ATP is synthesized from ADP and inorganic phosphate, and electrons are transferred to the coenzymes NADH and FADH2. This is a chemical cycle involving steps that complete the breakdown of glucose molecules. Pyruvate is transported from the cytosol to the mitochondrion, where further oxidation occurs before pyruvate enters the mitochondrion, loses a carboxyl group, releases CO2, and is further oxidized to create an acetyl group. Subsequently, the acetyl group combines with CoA to form acetyl. Coa. When oxygen is present in the cell, pyruvate enters the mitochondrion to finish the oxidation process, releasing CO2, producing NADH, ATP, and FADH2. The Krebs cycle happens in the matrix of the mitochondrion and for every glucose molecule in the cycle happens twice. Each glucose molecule 2 turns of the cycle produce 6NADPH, 2 FADH2, and 2 ATP in total.
Electron Transport Chain and Oxidative Phosphorylation
The electron transport chain transfers energy from electrons in a series of coupled reactions that establish an electrochemical gradient across membranes. These reactions occur in chloroplasts, mitochondria, and prokaryotic plasma membranes. In cellular respiration, electrons delivered by NADPH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen. Aerobic prokaryotes also use oxygen, while anaerobic prokaryotes use other molecules.
By understanding the cellular respiration process and the Krebs cycle, organisms can efficiently utilize the energy stored in biological macromolecules to function and survive.
