Glucose is a form of sugar and plays an important role in energy transformation in the body. You obtain glucose from eating plant-based foods, such as potatoes and grains; your body also stores glucose in your liver in the form of glycogen. Glucose is the primary building block of a chemical called adenosine triphosphate, or ATP -- the fuel that runs every process in your body -- in a process known as the Krebs cycle.
Krebs Cycle
When you eat, your digestive system breaks down carbohydrates into glucose, and absorbs the glucose into your bloodstream. All your cells absorb the glucose and convert it to a substance called pyruvate. Tiny structures called mitochondria take the pyruvate and combine it with oxygen to make ATP. Each glucose molecule makes two pyruvate molecules and each pyruvate molecule makes one unit of ATP.
Why Glucose is Used
Glucose is a very simple, single chain sugar known as a monosaccharide. Monosaccharides have very weak chemical bonds; this means they break apart easily. Your body has to use energy to make energy. The more energy it has to use in the transformation process, the less energy it has for other processes such as brain function or your heartbeat. Glucose also breaks down quickly so, in addition to using fewer resources to make ATP, it also makes ATP available to the body faster. Your body can also use fats and proteins in energy transformation, but not as efficiently.
Fat and Energy
In the absence of adequate glucose, your body breaks down fats to make ATP. Because fat is not accessible in its original form, your body has to first break the fat down into glycerol and fatty acids. The glycerol is a type of sugar and converts to pyruvate in the cell. Because the fatty acids are not sugars, the body has to break them down into acetyl CoA, a chemical that helps turn pyruvate into ATP. The extra steps involved in using fat in energy transformation take longer and require more of the body's resources.
Protein and Energy
In the absence of glucose and fat, your body breaks down protein to provide for energy. As with fat, protein is not accessible in its original form and needs to be broken down into amino acids. The body then needs to convert these amino acids into glucose to make the pyruvate required for ATP production. The extra steps required to use protein in energy transformation take longer and use more energy than glucose. Breaking down protein can also damage structures made of protein such as the heart, liver and other organs.
References
- "Principles of Anatomy and Physiology"; Gerard J. Tortora et al; 2010
- McGraw Hill: Anatomy and Physiology: How the Krebs Cycle Works
