Glucose - Ah, Sugar Sugar!

I love a good meal. Cooking is one of my favorite pastimes. I especially like to make cookies and cakes. I prepare a mean cheesecake! It is always a holiday favorite. But man does not live by cheesecake alone. Our cells primarily use sugar, or more specifically glucose, as food. We take in proteins, fats and carbohydrates as food or calorie sources and our body uses them as building blocks or as a means to supply or store glucose.

Glucose is a simple sugar with a chemical formula of C₆H₁₂O₆. The name "glucose" comes from the Greek word glukus, meaning "sweet" and the suffix "-ose" denoting a sugar. It exists in a number of isomers but the one we utilize is D-glucose or dextrose. You might remember this as the main building block of cellulose from the Cotton-Picking Carbohydrate blog. Our bodies can not metabolize cellulose to produce glucose as ruminants (animals that chew the cud) can due to their multiple stomachs. We get our glucose from other sugars, most notably sucrose or table sugar, or from more complex carbohydrates such as starches.

In our bodies glucose is metabolized by cells either through aerobic or anaerobic respiration. Aerobic (with oxygen) is the most utilized and yields the most energy as Adenosine triphosphate or ATP. Anaerobic is only used when insufficient oxygen is available to support aerobic respiration. The complete cellular respiration reaction includes glycolysis, pyruvate decarboxylation and the Krebs Cycle. Ultimately, glucose is metabolized to just water and carbon dioxide.



Glucose metabolism and various forms of glucose during the process

• Glucose-containing compounds are digested and taken up in the intestines, including starch, glycogen, di- and mono-saccharides.
  
• Glucose is stored mainly in the liver and muscles as glycogen.
  
• Glucose is distributed and utilized in tissues as free glucose.
  

Now just because glucose is our primary energy source, it is not a license to eat another donut. Our body is using glucose constantly, more or less at any moment depending on our metabolic rate. Thus when we are asleep, our metabolic rate and our use of glucose is down. When we are running a marathon, it goes up considerably. It would be impossible to supply a steady stream of glucose to our cells under all situations by just eating sugar. Our bodies need to store and release the glucose in just the right amounts and at just the right time. Thus some of the calories we eat are stored as glycogen, a protein with many branched chains of glucose molecules attached, waiting to be used as glucose. Glycogen is synthesized in the liver and muscle tissue as a storage depot for quick release glucose.

Our bodies also store fat as adipose tissue to be used as a slow release energy source. Fat in the form of triglycerides, an ester derived from glycerol and three fatty acids, can be used to generate glucose. Fat also is metabolized by the Krebs Cycle to generate ATP without glucose.

In order for our bodies to use glucose, it must get into the cell. This is the job of insulin, a protein hormone created in the pancreas and released as needed to maintain proper blood sugar concentration. Our cells can not absorb the glucose from the blood unless insulin is present. When a cell has insulin attached to its surface, the cell activates other receptors designed to absorb glucose from the bloodstream into the inside of the cell.

As you can see our bodies would not be able to go without glucose. It is the starting point for energy creation for almost all of our bodies functions. Without it, life would not be so "sweet!"

Psalm 119:103 - "How sweet are your words to my taste, sweeter than honey to my mouth! (NIV)"