Glucose is the most common sugar found in the blood and is one of the main energy sources in the body. Most carbohydrates are broken down into glucose. It can be stored in the liver, muscle and other tissues, or used to produce energy-containing compounds, especially ATP. Glucose metabolism refers to the chemical reactions glucose undergoes in the cells in order to store or utilize it, also known as its metabolic pathways.
Storage and Gluconeogenesis
In a fed state, the body takes up glucose and other nutrients into the cells. Glucose is a single sugar molecule. In storage cells, the single sugar molecules of glucose can be linked together to form large, branched chains called glycogen. In a fasting state, the glycogen is broken down to keep the blood sugar elevated. In addition, tissues such as the liver can undertake gluconeogenesis, which is the synthesis of glucose from precursor molecules. Glucose travels in the blood and is taken up by cells under the influence of insulin.
Glycolysis
After glucose enters the cell, it enters a pathway known as glycolysis. Glycolysis is a series of nine chemical reactions in which glucose is split in half from a six-carbon molecule into two three-carbon molecules that undergo further changes. These changes result in the net synthesis of two ATP molecules per glucose molecule. ATP, or adenosine triphosphate, is an energy-carrying molecule stored by cells and used to perform work.
Tricarboxylic Acid Cycle
The last chemical synthesized by glycolysis is pyruvate. Pyruvate can be converted into lactic acid, or enter the tricarboxylic acid cycle, also known as the TCA cycle or Krebs cycle. This cycle creates more energy-carrying compounds, as well as electron-carrying compounds that are used by a part of the cell called the mitochondiria, which is able to synthesize many ATP molecules.
Oxidative Phosphorylation
Oxidative phosphorylation passes electrons from the molecules made in the TCA cycle through proteins in the mitochondria. These are used to fuel a protein called ATP synthase, which makes many molecules of ATP. One molecule of glucose can be used to make 32 to 38 molecules of ATP.
References
- "Lehninger Principles of Biochemistry"; David L. Nelson, et al.; 4th Ed., 2004
- "Molecular Biology of the Cell"; Bruce Alberts et al.; 4th Ed., 2002
