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How Does Glycolysis Occur?

All life on Earth performs glycolysis to break down food (glucose and glycerol) and turn it into energy. Glycolysis is performed in the cytoplasm of the cell and produces a net product of two adenosine triphosphate (ATP) and two coenzyme nicotinamide adenine dinucleotide (NADH), turning glucose into two pyruvate acids. ATP transports chemical energy throughout cells for metabolic reactions and NADH forms water and energy stored as ATP.

Obtaining Glucose
- Getting glucose into an organism's cells is the first step of glycolysis. Animals obtain glucose by eating and plants through photosynthesis. When an animal eats, it directly takes in glucose into its system along with other nutrients. Glucose is stored in the body until it can be broken down and turned into energy. In plants, however, the method is different and plants obtain glucose via photosynthesis. Photosynthesis occurs when a plant takes in light, water and carbon dioxide and creates oxygen and glucose.
Breaking Down Glucose
- Glucose must be primed by expending two molecules of ATP before it can be broken down, which means that ATP must be stored and ready for use for the body to create more ATP. To prime the six carbon glucose molecules, each molecule of ATP transfers one phosphate, creating a six-carbon molecule with two phosphates. The two ATP molecules then become ADP, and the six-carbon molecule is then split in half to form two three-carbon sugar phosphate molecules.
Converting to Pyruvate Acid
- The next step in glycolysis requires that each three-carbon sugar phosphate molecule must transfer two electrons and one proton to one NAD each, which then forms two NADH. Oxidation causes the two three-carbon sugar phosphate molecules to transfer phosphate to ADP, transforming it back to ATP. These molecules add phosphate to two ADP molecules, in total creating four ATP molecules. The three carbon molecules without phosphate become pyruvate molecules, which are stored and can be burned for energy later on through the Kreb's Cycle, which is a cycle of reactions involved in producing high-phosphate compounds.
Final Outcome
- Because it takes two ATP molecules to begin glycolysis, when four ATP molecules are created, then the net number of ATP molecules are two. Phosphate added to NAD molecules creates two NADH. Finally, the six-carbon glucose molecule, which is the starting molecule in the glycolysis process, becomes two three carbon pyruvate molecules. The process of glycolysis therefore creates a small amount of energy, which can be transported and used throughout cells.

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