Explain the glycolysis in detail.

Glycolysis is the breakdown of one molecule of glucose (6-carbon) into two molecules of pyruvic acid (3-carbon) in the cytoplasm, without the need for oxygen.

Steps:

1. Glucose is converted into glucose-6-phosphate, using 1 ATP.
2. Glucose-6-phosphate changes into fructose-6-phosphate.
3. Fructose-6-phosphate is converted into fructose-1,6-bisphosphate, using 1 more ATP.
4. Fructose-1,6-bisphosphate splits into two 3-carbon compounds: glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. The latter is converted into glyceraldehyde-3-phosphate, so we get 2 molecules of it.
5. Each glyceraldehyde-3-phosphate is oxidised to 1,3-bisphosphoglyceric acid; NAD takes up hydrogen to form NADH₂.
6. 1,3-bisphosphoglyceric acid gives 3-phosphoglyceric acid, forming ATP.
7. 3-phosphoglyceric acid changes to 2-phosphoglyceric acid, which loses water to form phosphoenolpyruvic acid.
8. Phosphoenolpyruvic acid gives pyruvic acid, forming ATP.

Net result per glucose: 2 ATP used, 4 ATP formed, so net gain is 2 ATP; also 2 NADH₂, 2 pyruvic acid and 2 water molecules.

In aerobic respiration, pyruvic acid enters the mitochondria for the Krebs cycle. In anaerobic conditions, it is converted into lactic acid or ethanol.