Respiration can be defined as the oxidation of the end products of glycolysis with the storage of the energy in the form of ATP. Cellular respiration occurs when oxygen is available, and the products are carbon dioxide and water. There are three main pathways in the cellular respiration process. These are: oxidation, the citric acid cycle, and the respiratory chain. Pyruvate oxidation in eukaryotic cells occurs inside the mitochondrion in the inner membrane, and in prokaryotes on the inner face of the plasma membrane.

This step is the crucial link between the steps of glycolysis and cellular respiration. In this step, is oxidized into acetate. Pyruvate from the end of the glycolysis cycle diffuses into the mitochondria, where it gets oxidized. The three-carbon loses two of its hydrogen atoms and also a carbonyl grouping. A two-carbon acetyl group, free energy, and carbon dioxide are made. Coenzyme A links to the acetyl group, and captures the free energy that is there.

A little of the energy that was made gets saved when NAD+ is reduced to NADH+H+. Some of the rest of the remaining energy is stored temporarily when the acetyl group combines with CoA. Pyruvate dehydrogenase complex catalyzes the reaction. This catalyzing agent alone contains 72 polypeptide chains.

Acetyl coenzyme A is the product of this cycle, and moves into the citric acid cycle to continue the process. The citric acid cycle receives the acetyl CoA, and begins its system. This system occurs inside the mitochondrion matrix in eukaryotes and in the cytoplasm in prokaryotes. The inputs that start the CAC are water, acetyl, and oxidized electron carriers. For every acetyl group the cycle goes over, there are usually two carbons in the form of carbon dioxide removed, and four pairs of hydrogen atoms are used to reduce carrier molecules. The two-carbon acetyl group combines with the four-carbon and in turn form a six-carbon citrate.

The energy that was stored from before in the CoA drove that reaction. Here the coenzyme A goes away to be recycled, as it was just a carrier molecule for the acetyl group. In the next reaction, the citrate from before gets reorganized, and it becomes iso citrate. This then gets converted into alpha-Alea Gelvinketoglutarate when one carbon dioxide and two hydrogen's are taken away. This part of the reaction series makes a large drop in the free energy that is around. The energy that does get released gets stored in NADH+H+.

The next part of the reaction chain is when the five-carbon alpha-k molecule gets oxidized into a four-carbon molecule called succinate. Here again, carbon dioxide is released, some energy is preserved with the combination of CoA and succinate, and some of the oxidation energy is stored in NADH+H+ again. The energy that is in the CoA is then removed and used to make GTP from GDP and Pi. This is an example of on the substrate level. Next, ADP is used to make ATP by using GTP. More free energy gets released when the CoA gets oxidized to yield.

During this, two more hydrogen's are moved to an enzyme that has the carrier FAD. One more NAD+ reduction occurs and makes from ma late. Water is added, which makes an OH- group, and the hydrogen from the group gets taken off in the next step to make NAD+ reduce to NADH+H+. Water is used here, and in turn provides lots f energy because of its abundance. The finishing product that we have is, however, this process has to be repeated again. The final product gets to combine with another CoA and go around the whole circle again.

This happens two times per glucose that goes through glycolysis. The CAC reactions together are one of the most efficient energy gatherers of any of the systems along the process of respiration. The end outputs of the CAC are: 2 carbon dioxide molecules, ATP, 2 NADH and an FADH 2 molecule. From this phase, the respiratory chain takes over. The actions of the respiratory chain occur for prokaryotes on the inner face of the plasma membrane, and for eukaryotes inside the mitochondrion in the inner membrane. Another name for the respiratory chain is electron transport.

There are three large protein complexes that contain carrier molecules and their associate enzymes in the electron chain. These complexes are stuck to the folds of the mitochondrion membranes, or the crista e in eukaryotes or the plasma membrane of aerobic prokaryotes. A small protein, called cytochrome c, lays between the inner and outer mitochondrion membranes. Ubiquinone, or Q, is a little nonpolar molecule that is inside the hydrophobic inside of the phospholipid bi layer and moves freely inside it. NADH+H+ takes hydrogen's to the Q, using the protein complex NADH-Q reductase. This then passes the hydrogen's down to Q, which then makes QH 2.

NADH+H+ proteins shuttles electrons through the inner membrane of the mitochondria. There is a high concentration in the area between the two membranes. The lipid bi layer is impermeable to hydrogen's. The electrons are originally accepted fro NADH+H+ and taken in by NADH-Q reductase. More electrons come from succinate through FADH 2, which are accepted through succinate-Q reductase.

Both of those sets of electrons get put together into the Q. Then they move into the next step, which is where cytochrome c complex comes in. Cytochrome c oxidase gets the electrons and passes them through to the oxygen. Then the oxygen gets two hydrogen ions and this makes water. Electrons can be transported within every complex and from complex to complex. More electrons come from the past reactions of the CAC from the succinate to reaction step.

The usage of the three large protein complexes results in the pumping of protons across the membrane on the inner mitochondria. When the protons return across the membrane, ATP is produced. For every pair of electrons that go into the respiratory chain, there are three Atp made. This ending process is called ATP synthesis. The protons return to the outside because of the imbalance between the sides of the membranes.

They get back out by passing through ATP from the inner membrane. This generates ATP when the movement occurs. When the protons move back and forth, there is a difference in the electronic charges across the membranes, as well as a difference in proton concentration. The movement of the protons across the membrane and the reasons that it occurs is called the proton-motive force.

At the end of this total chain, there are 2 NADH produced (which came from glycolysis), 2 NADH (from oxidation), 6 NADH (from CAC), and 2 FADH 2 (from CAC). The coupling of the protons moving through and the formation of ATP is called the mechanism.