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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.
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