Cellular Respiration & Metabolism

Metabolism refers to all the chemical reactions in the body that either create energy for the body to use or that require energy in order to build the structural and functional systems. Cellular respiration is one step in the metabolic reactions that provides energy for use by the body’s cells.

Catabolism

The metabolic reactions that create energy are called catabolism. This process begins during digestion when nutrients are broken down into glucose, amino acids and fatty acids that can be absorbed into the blood. However, they are still not in a chemical form that can be used at the cellular level. They need to be converted into ATP.

ATP

ATP is the acronym for adenosine triphosphate. ATP is the chemical form of energy used by every cell in the body. As it is used, it breaks down and is recycled to be used again for the production of more ATP.

Cellular Respiration

Cellular respiration is the metabolic process that converts biochemical energy from glucose into ATP. This is accomplished through a series of chemical reactions called oxidation and reduction reactions. During oxidation, molecules lose hydrogen and electrons. A reduction is the opposite reaction in which another molecule gains the hydrogen and electrons. Cellular respiration is a complicated chemical process that has three phases: Glycolysis, the Krebs Cycle and the electron transport chain.

Glycolysis

In this phase, glucose goes through a series of chemical reactions that result in converting each molecule of glucose into two molecules of pyruvate. Two molecules of ATP are also released. Glycolysis does not require oxygen to produce pyruvate, but what happens next depends on it. In the presence of oxygen, pyruvate enters a reaction in which it attaches to coenzyme A and becomes acetyl-coenzyme A. It must be in this form to enter the Krebs Cycle.

The Krebs Cycle

Acetyl-coenzyme A enters the mitochondria of the cell and the Krebs Cycle begins. During this phase, the acetyl-coenzyme A combines with oxaloacetic acid to form citric acid, which is why the Krebs Cycle is also called the citric acid cycle. The molecules of citric acid go through a series of reactions in which the acids are oxidized (lose hydrogen) and the hydrogen is picked up by coenzymes. The hydrogen, in the form of NADH and FADH, enters the next phase.