Life Cycle of Glucose

Glucose is probably the most important sugar to humans and the only one that can be utilized for nutrition. All cells in the body need glucose---especially the brain. Glucose, while not having a "life cycle" in the strictest sense, does undergo changes to be used as energy.

The Beginning

• In photosynthesis, sunlight and water turn carbon dioxide into glucose in plants. Plants store glucose as either starch or cellulose. Cellulose gives fruits and vegetables such as apples and celery their crunch.

Conversion

• Starch from the plant is consumed by animals and converted into glucose, to be used as energy, or glycogen, which is stored for later use.

Respiration

• When glucose is ready to be used for energy it undergoes respiration---the process that turns what we eat into energy to be used in the body. During glycolysis, which is the portion of respiration that happens in the absence of oxygen, glucose becomes pyruvate, a salt. Pyruvate is converted into acetyl-CoA, which provides balance between the metabolism of carbohydrates and fats.

Citric Acid Cycle

• Acetyl-CoA enters the citric acid cycle when it generates usable energy---including adenosine triphosphate (ATP), which is the energy currency of the body.

The End

• Acetyl-CoA is shuttled into the electron transport chain, a network of smaller reactions between an electron donor and an electron acceptor, wherein more ATP is produced and energy is released. The final product of the electron transport chain is water.