Sugars are used by many chemoheterotrophs as an important source of carbon and energy. Indeed, complete oxidation of glucose using oxygen as a terminal electron acceptor has a free energy change of –2,883.0 kJ/mol. What strategy do cells use to minimize the amount of that energy that is lost as heat during the catabolism of sugars?

Sugars are used by many chemoheterotrophs as an important source of carbon and energy. Indeed, complete oxidation of glucose using oxygen as a terminal electron acceptor has a free energy change of -2,883.0 kJ/mol. What strategy do cells use to minimize the amount of that energy that is lost as heat during the catabolism of sugars?

A. Energy is harvested using a series of smaller oxidations.

B. The cells employ high-capacity energy carriers (e.g., ΔG°' of hydrolysis ~ -1000 kJ/mol).

C. Oxidation is directly coupled to biomass synthesis.

D. The oxidation reaction occurs within insulated organelles.

E. Oxidations of sugars directly power membrane-bound ATP synthases.

Solution

The free energy of –2,883.0 kJ/mol is too high for single metabolic reactions in one go. In order to judicially use this energy, it is to be broken down into smaller units. Therefore, the glucose oxidation is broken down into a series of chain reactions by cell where at each stage a certain amount of energy in the form of energy molecules such as ATP, ADP ,NAD+ and NADH etc. is released.

Glucose oxidation is divided into three set of reactions – 1) glycolysis, 2) cytpchrome pathway and 3) kerb cycle with certain amount of energy released at each phase. The overall energy released in equal to –2,883.0 kJ/mol.

Hence, option A is correct