Recall Which organelles are the sites of energy-yielding reactions?

Cellular respiration is an essential process that occurs in the cells of all living organisms. It is the way cells convert the energy stored in glucose into a form they can use, called ATP (adenosine triphosphate). This process requires oxygen and produces carbon dioxide and water as byproducts.
Cellular respiration takes place inside the mitochondria, often referred to as the powerhouse of the cell. This process involves several stages:

• Glycolysis
• Citric Acid Cycle (Krebs Cycle)
• Electron Transport Chain

During glycolysis, glucose is broken down into pyruvate in the cytoplasm, producing a small amount of ATP. The pyruvate then enters the mitochondria, where the Citric Acid Cycle occurs, releasing electrons that are transported through the Electron Transport Chain to generate a larger amount of ATP.

ATP, or adenosine triphosphate, is the energy currency of the cell. It is the molecule that cells use to store and transfer energy for their activities. The production of ATP is a critical function of cellular respiration, ensuring that cells have a continuous supply of energy.
Within the mitochondria, ATP production primarily occurs during the Electron Transport Chain stage. High-energy electrons, carried by molecules like NADH and FADH2, travel through proteins in the inner mitochondrial membrane.
These electrons release energy used to pump protons across the mitochondrial membrane, creating a gradient. The flow of protons back across the membrane through the enzyme ATP synthase drives the production of ATP from ADP (adenosine diphosphate) and inorganic phosphate (Pi).

Energy-yielding reactions are those reactions that result in the release of energy, which is then captured in the form of ATP. These reactions are a key part of cellular respiration and take place primarily in the mitochondria.
The steps leading to energy production include:

• Breaking down of glucose into pyruvate during glycolysis
• Oxidation of pyruvate in the Citric Acid Cycle
• Transfer of electrons through the Electron Transport Chain

The Citric Acid Cycle, also known as the Krebs Cycle, fully oxidizes the organic molecules and generates electron carriers NADH and FADH2. These carriers hold high-energy electrons that fuel the Electron Transport Chain. Here, the energy from electrons is used for proton pumping to create a proton gradient. This gradient is essential for the final synthesis of ATP.