Cellular Respiration: Glycolysis

Slide 2 Notes

Glycolysis is only one segment of cellular respiration (Pruitt, Underwood, 2005). Glycolysis is the most primitive of the types of cellular respiration. Glycolysis does not required oxygen so it is called anaerobic. There are four major steps in glycolysis. The process begins with a molecule of glucose. The glucose molecule is exposed to 2 ATP molecules which results in the glucose molecule picking up two phosphates. The result of this reaction is fructose diphosphate and two ADP molecules. Then fructose diphosphate is split into 2 glyceraldehyde phosphate (Respiration, n.d.). Then a free floating phosphate is added to each molecule of glyceraldehyde phosphate and NAD+ picks up a particle of hydrogen from each molecule of glyceraldehyde phosphate. The result of both of these reactions are 2 3-diphosphoglycerate . Finally both molecules of 3-diphosphoglycerate are exposed to 2 ADP a piece which result in 4 ATP. The net result of glycolysis is 2 ATP and 2 NADH. 

Slide 3 Notes

During the first step in glycolysis there is actually a loss of two ATP. A phosphate is taken from both ATP in order to make the resulting fructose diphosphate more reactive. This step also releases two ADP into the cellular plasma which will be used later. 

Slide 4 Notes

The second step is simply splitting fructose diphosphate which makes 2 glyceraldehyde phosphate. By doing this glycolysis is able to double the amount of ATP produced. 

Slide 5 Notes

The third step entails harvesting a hydrogen molecule from each glyceraldehyde phosphate and adding it to NAD+ making NADH, which is used later on in cellular respiration. Also a free floating phosphate is added to glyceraldehyde phosphate to make 2 3-diphosphoglycerate.

Slide 6 Notes

In the final step ADP is used to harvest 2 phosphates from each 3-diphosphoglycerate.  The result of this reaction is 4 ATP molecules and pyruvate, which is used in the next step of cellular respiration. So in all the net result is 2 ATP, 2 NADH, and 2 pyruvate molecules. There is actually another step in glycolysis, but it is only used when oxygen is in short supply. Say that a runner is in a marathon. They have already ran for an hour and the runners cells are producing ATP (energy) at a rate that can keep up with the runner’s demands. There is a steep hill coming up soon. As the runner starts up the hill the demand for ATP outstrips the supply of oxygen, which is used to yield the bulk of ATP during cellular respiration. In that case the runner needs energy now but cannot get it through the rest of the cellular respiration cycle. So instead of glycolysis ending with pyruvate it is extended one more step to get more energy. A hydrogen molecule from NADH regenerates pyruvate making lactic acid, which in turn yields more energy. When too much lactic acid builds up in the runner’s cell the result is what we would call fatigue. But after the hill the runner slows back down to a normal pace and cellular respiration continues through the Krebs cycle and the electron transport chain.

References

Respiration. (n.d.) Retrieved January 16, 2007, from BioInquiries Website: http://higheredbcs.wiley.com/legacy/college/pruitt/0471473219/bioinquiries/ch10/bioinquiry_section_10_3.html

Pruitt, P.L., Underwood, L.S. (2005). BioInquiry: Making Connections in Biology. Danvers, MA: Wiley.

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