Glucose-6-phosphate is a modified glucose molecule that your cells make from the glucose -- and in some cases, from other sugars -- that you eat. You need glucose-6-phosphate for a variety of reasons: it is an important reactant in many metabolic reactions and helps keep glucose inside your cells.
Chemistry
Glucose-6-phosphate shares much of its chemical structure and formula with glucose, which is a sugar. Technically, glucose is a monosaccharide, meaning that it's a sugar made up of a single ring structure. It has the chemical formula C6H12O6. Glucose-6-phosphate is identical to glucose, except that in place of one oxygen and hydrogen atom on glucose, glucose-6-phosphate has a phosphate group, or PO4.
Synthesis
Your cells make glucose-6-phosphate immediately from all glucose that enters the cell. Body cells use an enzyme called hexokinase to accomplish this reaction. Hexokinase is a protein that helps the reaction converting glucose to glucose-6-phosphate happen much faster than it otherwise would. One primary reason for converting all glucose to glucose-6-phosphate right away is that while glucose can escape a body cell, glucose-6-phosphate can't -- it's trapped inside.
Energy From Glucose
One of the things your cells do with glucose, once it's been transformed into glucose-6-phosphate, is burn it for energy. This takes place through a process called glycolysis, followed in most cases by another process called the Krebs cycle. Glycolysis results in a glucose molecule splitting into two smaller molecules called pyruvate -- this reaction yields energy that the cells can use for a variety of purposes. The Krebs cycle burns pyruvate into carbon dioxide, yielding more energy.
Synthesis of Glycogen
Another important use of glucose-6-phosphate is the generation of glycogen in your liver and muscle cells. Glycogen is a carbohydrate made up of long chains of glucose that the liver and muscles store so that they -- and the rest of the body cells -- have access to glucose during times of fasting. The enzymes that make glycogen require glucose-6-phosphate as a starting material.
From Other Sources
Glucose-6-phosphate is so important to your body cells that you can actually make it from non-glucose starting materials. For example, when you consume milk, you take in the sugar lactose, which consists of a molecule of glucose bound to a molecule of the related sugar galactose. Your cells can't convert galactose directly into glucose, but they can make it into glucose-6-phosphate, and can they either burn it for energy or use it to make glycogen.
References
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
