Physiology, Glucose

Excerpt

Glucose is a 6-carbon structure with the chemical formula C₆H₁₂O₆. Carbohydrates are ubiquitous energy sources for every organism worldwide and are essential to fuel aerobic and anaerobic cellular respiration in simple and complex molecular forms. Glucose often enters the body in isometric forms such as galactose and fructose (monosaccharides), lactose and sucrose (disaccharides), or starch (polysaccharides). Excess glucose is stored in the body as glycogen, a glucose polymer, utilized during fasting. In addition, glucose can be produced through gluconeogenesis, a process involving the breakdown of fats and proteins. Given the paramount importance of carbohydrates in maintaining homeostasis, numerous sources contribute to glucose production.

The sugar molecule travels through the blood to energy-requiring tissues when glucose is in the body. Glucose undergoes a series of biochemical reactions, releasing energy as adenosine triphosphate (ATP). ATP derived from these processes fuels virtually every energy-requiring process in the body. In eukaryotes, most energy derives from aerobic (oxygen-requiring) processes, which start with a glucose molecule. Glucose is initially broken down through the anaerobic process of glycolysis, producing some ATP and pyruvate as end products. Under anaerobic conditions, pyruvate converts to lactate through reduction. Conversely, under aerobic conditions, the pyruvate can enter the citric acid cycle to generate energy-rich electron carriers that produce ATP at the electron transport chain.