Cellular Respiration

Cellular respiration takes place for cells to use energy from food to function by producing ATP (Adenosine Triphosphate). The process can be divided into three parts: Glycolysis, citric acid cycle, and electron transport chain.

 

Glycolysis:

Glycolysis takes place in the cytoplasm. When glucose enters glycolysis, it is divided into two 3-carbon molecules called pyruvates. In this process, extra protons and electrons are given off. When the NAD+ molecule combines with two protons, it is reduced to NADH, which carries electron with high energy. Also, during this process, 2 ATP molecules are used and 4 are produced, making a total production of 2 ATP molecules.

Glycolysis is unique because all organisms are able to use this process. This is the only step in cellular respiration that does not require the presence of oxygen to take place.

Citric Acid Cycle:

In between the citric acid cycle and glycolysis, each pyruvate molecule undergoes a process, in which the end carbon of each pyruvate is removed along with oxygen to produce carbon dioxide. Then, the 2-carbon molecule binds to a coenzyme A to form acetyl CoA.

The molecule acetyl CoA enters the cycle with water and binds to another molecule to form a citric acid. At the same time, the hydrogen of the sulfhydryl group on CoA is replaced. The remainder of the sulfhydryl group undergoes eight steps in the cycle, giving off carbon dioxide at two points. Also, along the way, NADH, FADH2, two electron carriers are formed. ATP is also produced in this cycle through substrate phosphorylation.

Electron Transport Chain:

In total, 10 molecules of NADH and 2 molecules FADH2 will enter the electron transport chain. They are oxidized back to NAD+ and FAD again when they lose electron to the chemicals in the transport chain. Then the chemicals pass the electrons off to the next chemical. The final acceptor of the electrons is oxygen, which uses them to form water.

At three specific points of the chain, when the chemicals pass on electrons, they must also release a proton into the intermembrane space. In order to balance the concentration of H+ in the intermembrane space, these protons want to go back into the mitochondrial matrix. An enzyme called ATP synthase lets the protons pass through and forms ATP and water molecules by combining ADP and phosphate group. This method of making ATP is called chemiosmotic synthesis.