Question

The energetics of glycolysis can be described using a roller coaster analogy. Initial energy is invested in glycolysis through phosphorylation (and hydrolysis of ATP). This is analogous to pulling the roller coaster up the hill. If glycolysis were a roller coaster, how would you envision the rest of the ride?

Answer 1

If investing energy is considered as pulling the coaster up the hill, then the initial steps of glycolysis when glucose is converted to glucose 6-phosphate and fructose 6-phosphate is converted to Fructose1,6-bisphosphate ATP is broken down to ADP and Pi and thus the roller coaster moves uphill. but in the next steps after production of two molecules of glyceraldehyde3-phosphate from fructose 1,6-bisphosphate, the glyceraldehyde 3-phosphate is converted to two molecules of1, 3,-diphosphoglycerate and in the process 2 NADH is made from 2 NAD+.

also in the next step from two molecules of 1, 3,-diphosphoglycerate to two molecules of  3- phosphoglycerate production 2 ATP molecules are made.

these two molecules of 3 phosphoglycerate changes to two molecules of 2 phosphoglycerate and subsequently to two molecules of phosphoenolpyruvate. these two molecules of phosphoenolpyruvate changes to 2 molecules of pyruvate and forms 2 ATP in the process. So total ATP formed is 4.

In the uphill task 2 ATP molecules were used, so the net gain of ATP from glycolysis is 4-2=2 ATP molecule. as ATP molecule is formed in the process, energy equivalents are made and so the roller coaster moves downhill, energy instead of being used is being made.

so the rest of the ride is down the hill, along the gradient.