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sharikendrick eNotes educator| Certified Educator

Adenosine Triphosphate (ATP)

ATP molecules are used for energy by cells. You can think of ATP as a molecule that stores energy in its bonds. When ATP bonds are broken, energy is released for cells to use. Cells are able to create ATP molecules for energy through the metabolism of glucose.

Origins of Glucose

  • Plant Cells: Plant cells can produce glucose molecules through the process of photosynthesis. During photosynthesis, plant cells are able to convert light energy from the sun into glucose molecules. The process of photosynthesis occurs in a plant cell organelle called the chloroplast.
  • Animal Cells: Animal cells acquire glucose through the consumption of food by the organism. 

Metabolism of Glucose into Energy Stored in ATP Molecules

  1. Glycolysis: Glycolysis begins the process of glucose metabolism. The process of glycolysis occurs in the cytoplasm, fluid which fills the innercellular space. During this process, each glucose molecule is converted into two molecules of pyruvate. 
  2. Cellular Respiration: Cellular respiration occurs in the mitochondria. During this process, oxygen from the environment is used to convert a pyruvate molecule into three molecules of carbon dioxide. The energy that is created during this process is stored in ATP molecules. There are three sub-pathways that occur during cellular respiration: pyruvate oxidation, the citric acid (Krebs) cycle, and the electron transport chain.
  3. Fermentation: Fermentation occurs in the cytoplasm of the cell in the absence of oxygen. During this process, a pyruvate molecule is converted to lactic acid or ethanol. These reacctions result in the production of ATP molecules. The process of fermentation is much less efficient at producing ATP molecules than the process of cellular respiration. 

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