How do you that bite of food into a chemical that a cell can recognize and use as energy ? the first step is altering the food into its component chemical compounds and then getting those molecules into your cells. That process is called digestion. Once inside ypur cells, the process of turing that bite of food into useful energy by celluler respiration begins. The process of digestion results with carbohydrates and other molecules being removed from the consumed food and transported into the bloodstream. From there, nutrients, like the carbohydrate glucose, will leave the bloodstream though a capillary wall and enter a tissue cell. Once inside the cell, celluler respiration will completely oxidize the glucose molecule, releasing high-energy electrons. The overall goal is to make ATP, a storage from of energy for most cells. Cellular respiration is a four-stage process that begins with glycolysis. Glycolysis literally means "splitting sugars" and it is the first step of cellular respiration, occurring in the cytoplasm of teh cell. Glycolysis consists of two distinct phases; an energy investment phase and an energy harvesting phase. In the energy investment phase, two ATP molecules transfer energy to the glucose molecole, forming a 6carbon sugar diphosphate molecule. This molecule splits, and the energy-harvesting phase begins. During this phase, the two 3-carbon molecules are converted to pyruvate, and ATP is formed. Glycolysis is a ten step reaction that involves the activity of multiple enzymes and enzyme assistants. In yhe process, a net of two moleculea of ATP, two molecules of piruvate and two "high energy" electron carrying molecules of NADH are produced. When oxygen is present, the pyruvate molecules and NADH enter the mitochondria and the next stage of cellular respiration begins. The stage of cellular respiration involves the movement of pyruvate into the mitochondria, where it undergoes oxidation. Each pyruvate molecule in converted into a compound called acetyl CoA. In the process of pyruvate oxidation, electrons are transferred to NAD producing NADH and a carbon in lost, forming of carbon dioxide. The next stage is the citric acid cycle, also called the Krebs cycle. Here, acetyl CoA will bond with a starting compound called oxaloacetate, and yhrough a series of enzymatic redox reactions, all carbons, hydrogens, and oxygens in pyruvate ultimately endbup as carbon dioxide and water. The pathway is called a cycle because oxaloacetate is the starting and ending compound of the pathway. For every glucose that enters hlycolysis the cycle completes twice, once for each for each molecules of pyruvate that entered the mitochondria. During pyruvate oxidation and the citric acid cycle a net of 8 NADH, 2 FADH, 2 ATP, and 6 CO2, are produce for each glucose molecules. In order to understand how the majority of the energy is produced by aerobic respiration, we need to follow the NADH and FADH2 molecules to the stage, the eoectron transport chain. The electron transport chain is a series of membrane-bound carriers in the mitochondria that pass electrons from one to another. As the electrons are transferred between the membrane proteins, the cell is able to capture energy and use it to produce ATP molecules. Proteins in the chain pump hydrogen ions across a membrane. When the hydrogen ions flow back across the membrane through an ATP synthase complex, ATP id synthesized by the enzyme ATP synthase. Oxigen acts as the terminal electron acceptor. By accepting electrones, oxygen is reduced to form water, a by product of the electron transport chain. All the high energy electron carriers from the previous stages of cellular. Respiration bring their electron into the chain. From this, the bulk of the ATP from the entirety of cellular respiration is produced : a net of 32-36 ATP. In summary, we have seen how the four stages of cellular resoiration are responsible for converting.
