Introduction to Glycolysis

What Are the Processes Involved?

Several processes occur sequencially in the pathway.

1. The six carbon monosacharide is split into two molecules of three carbon monosacharide.
2. The triose is oxidised at one end (carbon 1).
3. The oxidised triose is reduced at the other end (carbon 3).

During stage two ATP is synthesised from ADP. One mole of ATP is made for each mole of triose processed. Two moles of ATP for each hexose. Because the oxidation step is balanced with a reduction step a small amount of oxidising agent can be recycled indefinately.

Stage One - Lysis

This is acheived in several separate steps. Spliting glucose does not provide any free energy change but allows subsequent reactions to be doubled up. I.e. a rearrangement of atoms is done on both halves of glucose with a single set of enzymes.

Video for Windows Animation of Lysis 28k

Quicktime Animation of Lysis 92k

(All the intermediates and the product are phosphorylated but these phosphate groups have been ommited from the animation for clarity.)

Stage Two - Oxidation

Carbon one of the triose glyceraldehyde is oxidised. The aldehyde group becomes a carboxyl group and so the product is glycerate. There is a sufficient free energy change in this process for it to linked to the production of ATP from ADP and phosphate. If you count the oxygen atoms you will see that the product has one extra - this has not come from molecular oxygen but from water. The oxidising agent is NAD+

Video for Windows Animation of Oxidation 32k

Quicktime Animation of Oxidation 156k

(Intermediates are phosphorylated and the product undergoes acid disociation, so this animation is a bit of a simplification.)

Stage Three - Reduction

Over serveral steps carbon three of the oxidised triose is reduced. The hydroxyl group is removed. The product is lactate. Reduction occurs in anaerobic conditions because NADH needs to be recycled for use in the previous stage

(In aerobic conditions the oxidised triose is oxidised further and passed onto the TCA Cycle as acetate. )

Video for Windows Animation of Reduction 29k

Quickime Animation of Reduction 159k

(The actual product is the other optical isomer of lactate. This process occurs in several steps and this results in a change of position for the hydroxyl group on carbon 2.)