Glycolysis: Breaking Down Glucose for Energy

Glycolysis literally means 'sugar-splitting', and that's exactly what happens in your cell's cytoplasm. This process takes a 6-carbon glucose molecule and splits it into two 3-carbon pyruvate molecules, releasing energy your cells can actually use.

The process starts with glucose from your blood or stored glycogen getting 'pump-primed' with energy. Two ATP molecules are broken down to add phosphate groups to glucose, making it more reactive but also trapping it inside the cell - quite clever really!

Once activated, the phosphorylated glucose splits into two 3-carbon molecules called GP. Each GP gets oxidised, releasing hydrogen atoms that are picked up by the coenzyme NAD to form NADH. At the same time, four new ATP molecules are made through substrate level phosphorylation.

Key Point: Glycolysis uses 2 ATP but makes 4 ATP, giving you a net gain of 2 ATP molecules plus 2 NADH.

What happens to pyruvate depends entirely on oxygen availability. If there's plenty of oxygen around, pyruvate heads into the mitochondria for aerobic cellular respiration, where it can generate up to 32 ATP (recent estimates suggest 31). Without enough oxygen, cells switch to anaerobic fermentation in the cytoplasm, converting pyruvate to lactate in animals or ethanol in plants and microbes - but this only yields 2 ATP total.