Glucose is a sugar, a type of dietary carbohydrate your body uses as an energy source. Lactate, a product of glucose metabolism, is a compound your cells synthesize when they lack sufficient oxygen to fully break down glucose to release the energy it contains. The production of lactate serves both as a defense mechanism for your muscles and as a type of energy reserve. Glucose and lactate are therefore interrelated and essential molecules in your body.
Background
Your body derives 4 calories of energy from each gram of glucose you consume, and it does this through glycolysis, a cellular process. In glycolysis, a glucose molecule undergoes a series of biochemical reactions, with the help of a variety of enzymes, to create several intermediate molecules until the compound pyruvate is formed. In the process, adenosine triphosphate, or ATP, is also released, and your cells use ATP in the generation of energy. Depending on the availability of oxygen in your cells, pyruvate can be further metabolized to release more energy or can become reduced to lactate.
Aerobic Reaction
When your cells are well-oxygenated, pyruvate continues on in a process called the "tricarboxylic acid" cycle. This TCA cycle begins once pyruvate, generated by glycolysis, converts to acetyl-CoA, a molecule. Acetyl-CoA enters the TCA cycle and goes through several steps, catalyzed by different enzymes, ultimately to produce ATP and carbon dioxide. The TCA cycle also generates additional molecules that require oxygen to produce even more ATP, and therefore all these reactions occur in an aerobic, or oxygen-dependent, environment.
Anaerobic Reaction
Your cells work under anaerobic conditions when they lack sufficient oxygen to keep up with the demands of the TCA cycle. For example, when you exercise rigorously and continuously, your muscles require glycolysis to proceed at a rapid rate to meet the energy demands of your activity. Eventually, your breathing cannot keep up with your cells’ need for oxygen. At this point, you switch from aerobic energy production to anaerobic as pyruvate is unable to convert to acetyl-CoA and instead undergoes a reduction reaction to lactate. Lactate then accumulates in your muscle tissue.
Considerations
Both glucose and lactate offer benefits to your body. Glucose supplies a ready source of energy when your respiration can keep up with your physical demands. Lactate, once oxygen becomes available again, converts back to pyruvate and can enter the TCA cycle for energy production. Lactate also serves as a protective mechanism for your muscle tissue. The presence of this acidic compound results in a painful burning sensation in your muscles and encourages you to back off on your exercise intensity so you do not permanently damage your muscle fibers by overworking them.
References
- University of Illinois McKinley Health Center: Macronutrients: the Importance of Carbohydrate, Protein, and Fat; March 2008
- The Medical Biochemistry Page: Glycolysis; Michael King; August 2011
- Rensselaer Polytechnic Institute: Glycolysis and Fermentation; Joyce Diwan
- “Scientific American”; Why Does Lactic Acid Build Up in Muscles? And Why Does It Cause Soreness?; Stephen Ross; January 2006
- The Medical Biochemistry Page: TCA Cycle; Michael King; August 2011
