Glycolysis

Glucose + 2ATP + 4ADP + 2NAD+ ------> 2 Pyruvates + 2ADP + 4ATP + 2NADH

Overview

The purpose of glycolysis is to break down Glucose (6C) into 2 Pyruvate (3C). ATP is added to Glucose twice acting as activation energy, giving one phosphate to the glucose each. With one less phosphate, ADP leaves. Glucose with one phosphate on each end becomes Fructose-1,6-bisphosphate. This molecule is very unstable and will quickly split into G3P and DHAP. DHAP will be converted into G3P which will leave you with two G3P. The rest of the process will happen twice, once to each of the G3P. NAD+ is added to oxidize G3P, this process releases energy as ATP. H2O is taken out of the molecule and it becomes PEP. The phostphate group from PEP is transferred to ADP which produces ATP. This leaves one Pyruvate (3C) per G3P, so 2 Pyruvate in total. Glycolysis is only able to trap 2.1% of the energy that is available in Glucose because it is anaerobic (No oxygen involved).

The basic reactants and products of Glycolysis

Steps (Simplified)

  1. Glucose Activation: Two phosphates are added to glucose from 2ATP, the end product is fructose-1,6-bisphosphate

  2. Sugar Splitting: Because Fructose-1,6-bisphosphate is unstable, it splits into G3P and DHAP (which will also be converted to G3P).

  3. Oxidation: The two G3P are oxidized by NAD+, becoming NADH. This releases energy as one ATP per G3P.

  4. Formation of ATP: The phosphate groups on the molecule are given to ADP which makes one more ATP per G3P.

When?

Glycolysis is the first stage in cellular respiration. Because it is anaerobic it can be used as a quick energy source in a situation such as a short distance sprint. It produces a small amount of ATP so it isn't sufficent for multicellular organisms, but it is enough for a microorganism like bacteria.

Where?

Unlike the three other stages of cellular respiration which take place in various places in the mitochondria, Glycolysis takes place in the cytoplasm of the cell.

ATP Cost/Gain

Two ATP are used up in the process of Glycolysis and 4 ATP are produced. Two NADH (which account for 3ATP) are produced. This gives a net gain of 2ATP and 2NADH

Possible Pathways

The pyruvate made through glycolysis can go through a few different cycles depending on if you're using aerobic or anaerobic respiration

Anaerobic

The pyruvates can be used to create lactate (gaining hydrogen) in animals or ethanol (losing carbon) in plants. The lactate can be converted back into pyruvates later on and can then go through the rest of the aerobic cycle.

Aerobic

The pyruvates will go through the Kreb's cycle in order to produce more ATP and NADH. Both of these products will then go through the Electron Transport Chain to trap all of the possible ATP from Glucose

This video is very helpful if you need more help :)