Re: Why is Glucose used as THE food molecule for the cell?

The glucose molecule consists of six carbon atoms. In the cytoplasm, the glucose is cut in two molecules, each consisting of three carbon atoms. During such reactions the cell gains energy which is saved in the form of macroergic bonds (ATP molecules). All these reactions run in the absence of oxygen (anaerobic reactions) and are called glycolysis. Two or three ATP molecules are synthesized from energy of one glucose.

The next reactions that can follow occur in mitochondria of eukaryotic cells as the so-called citrate cycle (Krebs' cycle). A small amount of macroergic bonds is formed within this cycle; nevertheless, protons are broken away. The protons are moved into the space between the inner and the outer membrane of the mitochondrion. Protons return through the inner mitochondrial membrane where enzymes, which exploit their energy to make new macroergic bonds, are localized. In mitochondria, 36 new ATP molecules are synthesized from energy of one glucose.

Thus, mitochondria produces much more energy than glycolysis.

The ATP molecule is an uniform source of energy in cells. Macroergic bonds can be formed in several other molecules (e.g. GTP). Various organic molecules can be utilized for the citrate cycle and release their own energy for synthesis of macroergic bonds, too. (Admin note: although brain cells can only use glucose for "food", all other cells can use several carbohydrates, proteins, and fats to produce the acetyl-Coenzyme A necessary to fuel the citrate cycle in the mitochondria)

Warmest personal regards Josef