Aerobic respiration is a crucial metabolic process that converts biochemical energy from nutrients into adenosine triphosphate (ATP), with carbon dioxide (CO2) and water as byproducts. The process can be divided into several key stages, primarily the Krebs Cycle (also known as the citric acid cycle) and oxidative phosphorylation, which includes the electron transport chain (ETC).
The Krebs Cycle begins with the entry of two molecules of Acetyl CoA, which are derived from the breakdown of carbohydrates, lipids, or proteins. During this cycle, a total of four molecules of CO2 are produced, along with two ATP, two FADH2, and six NADH. The cycle regenerates oxaloacetate, which is essential for the continuation of the cycle.
Following the Krebs Cycle, the NADH and FADH2 produced are transferred to the electron transport chain during oxidative phosphorylation. Here, the electrons from NADH and FADH2 are passed through a series of complexes (from complex I to complex V), ultimately leading to the reduction of oxygen (O2) to form water (H2O). It is important to note that no additional CO2 is produced during this stage.
The theoretical yield of ATP from the complete oxidation of one glucose molecule through aerobic respiration can reach up to 38 ATP molecules, although the actual yield is often around 30-32 ATP due to various inefficiencies. Specifically, from the Krebs Cycle and oxidative phosphorylation combined, a total of 20 ATP can be generated, alongside the previously mentioned products: 2 FADH2 and 6 NADH.
In summary, aerobic respiration efficiently converts energy stored in nutrients into usable ATP, with the Krebs Cycle and oxidative phosphorylation playing pivotal roles in this metabolic pathway. Understanding these processes and their outputs is essential for grasping the overall energy metabolism in living organisms.