Question

In order for glucose to be used as an energy source, it is necessary that
(a) Glucose is formed from fructose.
(b) Glucose be degraded to carbon dioxide.
(c) 2 molecules of ATP be invested in the system.
(d) None of these.

Answer 1

Hint: Sugars are especially essential molecules of fuel, and they are oxidized into carbon dioxide and water in small steps.- It is not necessary for glucose to be produced from fructose in order to use glucose as energy.

Complete answer:
- After glycolysis, four ATP molecules are produced, but the net benefit from glycolysis is two.
- This is because the first half of the glycolysis process uses 2 ATP molecules. Hence, 2 ATP molecules are essential for glycolysis to take place.
- In the series of reactions known as glycolysis, from the Greek glukus, "sweet," and lusis, "rupture," the breakdown of food molecules is the degradation of glucose. Glycolysis creates ATP without the presence of molecular oxygen.
- It exists in most cells in the cytosol.
- A glucose molecule with six atoms of carbon is converted into two molecules of pyruvate during glycolysis, each of which contains three atoms of carbon.
- Two ATP molecules are hydrolyzed for each glucose molecule in order to provide energy to drive the early steps, but four ATP molecules are formed in the later steps.
- Consequently, with each glucose molecule broken down, there is a net gain of two molecules of ATP at the end of glycolysis.
So, the correct answer is ‘(c) 2 molecules of ATP be invested in the system’.

Note:
- Although no molecular oxygen is involved in glycolysis, oxidation occurs when electrons are withdrawn from some of the carbons extracted from the glucose molecule by NAD+ (producing NADH).
- The stepwise design of the process makes it possible to release the oxidation energy in small packets, so that much of it can be stored in activated carrier molecules rather than emitted as heat as a whole.