Cellular Respiration: Turning Food into Energy

Cellular respiration begins in the cytoplasm with glucose molecules from the food we eat.The first step of glycolysis requires an energy investment of 2 ATP molecules.Through a series of enzymatic reactions, the 6-carbon glucose molecule is split into two 3-carbon pyruvate molecules.This process produces a net gain of energy. Four ATP molecules are generated.Additionally, two NADH molecules are produced, which will be used later in cellular respiration.After subtracting the 2 ATP invested, glycolysis produces a net yield of 2 ATP molecules.These pyruvate molecules will now enter the mitochondria for the next stage of cellular respiration.Inside the mitochondria, the next stage of cellular respiration takes place.Pyruvate from glycolysis enters the mitochondrial matrix and is converted into acetyl-CoA.Acetyl-CoA then enters the citric acid cycle, also known as the Krebs cycle, a series of chemical reactions that completely break down the carbon compounds.The cycle proceeds through eight major steps, each catalyzed by specific enzymes.Throughout the cycle, high-energy electron carriers NADH and FADH₂ are produced, along with carbon dioxide as a waste product.As the cycle continues, it generates more electron carriers that will be used in the next stage of cellular respiration.These electron carriers will now move to the inner mitochondrial membrane for the final stage of cellular respiration.The electron transport chain is located in the inner mitochondrial membrane.The chain consists of four major protein complexes that work together to create an electrochemical gradient.High-energy electron carriers NADH and FADH2 deliver electrons to the chain.As electrons move through the complexes, hydrogen ions are pumped from the matrix into the intermembrane space.ATP synthase acts like a molecular waterwheel, using the flow of hydrogen ions to generate ATP.ADP and phosphate enter ATP synthase from the matrix side.As hydrogen ions flow through ATP synthase, it powers the conversion of ADP to ATP.The newly formed ATP molecules are released into the matrix.This process of oxidative phosphorylation produces the majority of ATP molecules, generating up to 34 ATP per glucose molecule.At the end of the chain, oxygen accepts the electrons and combines with hydrogen to form water.