BACKGROUND KNOWLEDGE

Glycolysis

Essential knowledge

Glycolysis is used in the carbohydrate metabolism and produces 2 molecules of pyruvate. These molecules can then enter the Krebs Cycle for further aerobic respiration or pyruvate can be converted to lactate, if no oxygen is available for ATP production.

The main function of the glycolytic pathway is the formation of 4 molecules of ATP. Remember that 2 molecules of ATP are needed at the beginning of the pathway. Therefore, you will get a net gain of 2 ATP per molecule of glucose.

The processes of glycolysis all occur anaerobically, this is in the absence of oxygen. This is an advantage as ATP can still be produced at a fast rate, but at the cost of an accumulation of lactate. Lactate is also called lactic acid, and as the name suggests, it is acidic and can be toxic in the body at higher amounts. Note that in the absence of oxygen, pyruvate is not converted to AcetylCoA to enter the Krebs Cycle.

It is important to recognize that glycolysis is an anaerobic process (an = without, aero = air). This means that glycolysis does not need to use oxygen in any chemical steps and that it occurs whether or not oxygen is present. It does not mean that glycolysis does only occur in the absence of oxygen.

The key enzymes are located in the cytoplasm. This is always a popular exam question which is easy to answer - make sure you know it.

Glucose enters the cell by facilitated diffusion. To maintain the diffusion gradient into the cell at high blood glucose levels, glucose is phosphorylated to glucose-6-phosphate (G6P). This also has the advantage that glucose does not leave the cell when blood glucose levels are low. Remember the principles of the diffusion gradient across a cell membrane.

The major chemical steps which you would need to know for your exam are shown in figure 1-01. Look at the background knowledge part of glycolysis for more detail about each step by clicking on the button below. This helps you to remember the names of the molecules and it also explains what exactly they do.

You need to know the names and the amounts of the products of glycolysis, what is required for glycolysis and also what is happening to pyruvate once it has been produced. Make sure you know figure 1-01 very well, knowing all the information on it.

Figure 1-01: The glycolytic pathway with all the essential chemical steps.