Molecular Biology - Cell Respiration

Cell respiration is the controlled release of energy from organic compounds to produce $ATP$. $ATP$ from cell respiration is immediately available as a source of energy in the cell.

Anaerobic cell respiration gives a small yield of $ATP$ from glucose. In humans, the product is lactate ($C_3H_6O_3$); in yeast and plants, the products are ethanol ($C_2H_5OH$) and carbon dioxide ($CO_2$).

Aerobic cell respiration requires oxygen ($O_2$) and gives a large yield of $ATP$ from glucose. It involves the link reaction, the Krebs cycle, and the electron transport chain.

Oxidation and reduction are chemical processes involving the transfer of electrons. In cell respiration, glucose is oxidized (loses hydrogen/electrons) and oxygen is reduced (gains hydrogen/electrons).

Glycolysis occurs in the cytoplasm and breaks down one $C_6H_{12}O_6$ molecule into two molecules of pyruvate ($C_3H_4O_3$), producing a net gain of $2$ $ATP$ and $2$ $NADH + H^+$.

The link reaction moves pyruvate into the mitochondrial matrix, where it is decarboxylated and oxidized to form an acetyl group, which then attaches to Coenzyme A to form $Acetyl-CoA$.

The Krebs cycle occurs in the mitochondrial matrix. For every turn of the cycle, $2$ molecules of $CO_2$ are released, $3$ $NADH + H^+$ are produced, $1$ $FADH_2$ is produced, and $1$ $ATP$ is generated via substrate-level phosphorylation.

Chemiosmosis occurs in the inner mitochondrial membrane. The electron transport chain creates a proton ($H^+$) gradient in the intermembrane space, which drives $ATP$ synthesis via $ATP$ synthase.