#biology #textbook #respiration

Aerobic respiration is a metabolic process used by cells to generate energy from glucose in the presence of oxygen. This process occurs in most living organisms, including animals, plants, and many microorganisms. It is the main method of energy production in cells that have access to oxygen and takes place primarily in the mitochondria of eukaryotic cells.

1. Glycolysis:

• Glucose (a 6-carbon sugar) is broken down into two molecules of pyruvate (a 3-carbon compound).

• This process generates a net gain of 2 ATP (adenosine triphosphate) molecules and 2 NADH (nicotinamide adenine dinucleotide) molecules.

• Glycolysis does not require oxygen and occurs in the cytoplasm.

2. Pyruvate Oxidation:

• Each pyruvate molecule is transported into the mitochondria and converted into acetyl-CoA (a 2-carbon molecule), releasing one molecule of carbon dioxide (CO₂) per pyruvate.

• NADH is also generated during this step.

3. Citric Acid Cycle (Krebs Cycle):

• Acetyl-CoA enters the citric acid cycle, where it is further broken down, and more CO₂ is released.

• The cycle generates additional NADH and FADH₂ (flavin adenine dinucleotide) molecules, along with 2 ATP molecules per glucose molecule (since 2 acetyl-CoA are produced from each glucose).

4. Electron Transport Chain (ETC) and Oxidative Phosphorylation:

• NADH and FADH₂ donate electrons to the ETC, which consists of a series of protein complexes embedded in the inner mitochondrial membrane.

• As electrons pass through the chain, they release energy that is used to pump protons (H⁺) across the mitochondrial membrane, creating a proton gradient.

• Oxygen acts as the final electron acceptor at the end of the chain, combining with protons and electrons to form water (H₂O).

• The energy from the proton gradient is used by ATP synthase to generate ATP. This process produces approximately 34 ATP molecules per glucose molecule.

Total ATP Yield:

• Glycolysis: 2 ATP

• Citric Acid Cycle: 2 ATP

• Electron Transport Chain: 34 ATP

• Total: Around 36-38 ATP molecules per glucose molecule.