All human activities are driven by energy that is produced within the the body. Cells of the human body depend on a molecule called adenosine tri-phosphate, or ATP, to provide energy. This is true for nerve cells which produce thought, muscle cells which produce movement and gland cells which produce hormones. ATP is produced from glucose through a process called metabolism.
ATP as an Energy Source
The ATP molecule contains one molecule of adenosine linked to three phosphate molecules. The phosphate molecules are all highly charged and in the natural state would repel each other. To create such a close packing of phosphate groups, a large amount of energy is required to build the ATP molecule. Since, as defined by the laws of thermodynamics, energy can neither be created nor destroyed, the energy used to build the ATP molecule remains present within the molecule and is released when ATP is broken down. Enzymes in our muscle, nerve and other cells can catalyze the breakdown of ATP and are called upon to release energy when needed.
Glucose
Glucose is a simple sugar, part of a class of molecules known as carbohydrates. The glucose molecule is the first component of the metabolic process through which ATP is produced within the body's cells. Through a stepwise series of chemical reactions called metabolism, glucose is converted into ATP. These reactions can occur in either the presence or absence of oxygen. Aerobic metabolism uses oxygen in the production of ATP while anaerobic metabolism does not.
Aerobic Metabolism
The most efficient way of converting glucose into ATP is through the metabolic pathway that uses oxygen in the final step. This oxygen-requiring series of chemical reactions is known as aerobic metabolism and can create a net of 36 molecules of ATP from each molecule of glucose. Aerobic metabolism produces carbon dioxide as its byproduct. Aerobic metabolism is the process favored in human cells.
Anaerobic Metabolism
The production of ATP from glucose is still possible in the absence of oxygen, although the anaerobic process yields just two ATP molecules from each molecule of glucose. The byproducts of anaerobic metabolism include alcohol and lactic acid. Many bacteria use anaerobic metabolism, and it is their production of alcohol through this process that converts the glucose in grape juice to the alcohol in wine.
Summary
Living organisms require ATP to serve as the energy source that drives their functions. Although glucose and ATP are not similar molecules, they are uniquely linked through the process of metabolism. Whether the metabolic pathway uses oxygen or not, glucose is always the starting point and ATP is the final end product.
References
- "Principles of Biochemistry - 4th Edition"; David L. Nelson; 2004
- "Exercise Science"; Warren Rosenberg and Ciaran Cullen; 2008
