Question

discussed two different methods of energetic coupling between exergonic and endergonic reactions. In your own words, describe each of these energetic coupling mechanisms and provide a specific example of each.

Answer 1

Ans: Energy coupling occurs between exergonic and endergonic reactions

1. Linking of an energetically favorable reaction like ATP hydrolysis with an energetically unfavorable endergonic reaction. The mechanism involved is through a shared intermediate like the product of one reaction is used as a reactant in the second reaction.

For example- Conversion of glucose to sucrose molecule with the use of ATP.

Here, ATP hydrolyzes and transfers a phosphate group to glucose and this reaction is favored energetically. The exergonic reaction of ATP hydrolysis is coupled with the endergonic reaction of converting glucose to be used in metabolic pathway during cellular respiration

2. By changing the shape of ion channels- ATP hydrolysis transfers one of its phosphate groups to the pump protein forming a phosphorylated “intermediate” form of the pump which is unstable. so it becomes more stable by changing shape, opening towards the outside of the cell, and releasing ions outside.

Example- Na+/K+ pump.