Question

Which of the following statements correctly describes some aspect of ATP hydrolysis being used to drive the active transport of an ion into the cell against the ion's concentration gradient? (see book section: Concept 8.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously and see book section: Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions)
A) The hydrolysis of ATP is endergonic, and the active transport is exergonic.
B) This is an example of energy coupling.
C) Both ATP hydrolysis and active transport are spontaneous because they result in an increase in entropy of the system.
D) Neither ATP hydrolysis nor active transport is spontaneous.
E) ATP is acting as a transport protein to facilitate the movement of the ion across the plasma membrane.

Answer 1

Answer:

B) This is an example of energy coupling

Explanation:

Energy coupling is a process by which cells carry out thermodynamically unfavorable, endergonic (energy-requiring) reactions to other exergonic (reactions that liberate free energy) reactions.

Reactions which are endergonic do not occur spontaneously as they result in a decrease in entropy and a positive free energy change, ∆G.

Exergonic reactions occur spontaneously as they result in an increase in entropy and have a negative free energy change, ∆G.

For example, the active transport of ions against their concentration gradients in cells is a non-spontaneous endergonic process which is coupled to the hydrolysis of ATP, an exergonic process in other for the reaction to proceed. ATP hydrolysis phosphorylates an amino acid side chain in the transport protein which then drives the forward process of transport of the ion.

Considering the above,

Option A: The hydrolysis of ATP is endergonic, and the active transport is exergonic is false because ATP hydrolysis is exergonic while active transport is endergonic.

Option B: This is an example of energy coupling is true.

Option C: Both ATP hydrolysis and active transport are spontaneous because they result in an increase in entropy of the system is false because only ATP hydrolysis is spontaneous

Option D: Neither ATP hydrolysis nor active transport is spontaneous is false because ATP hydrolysis is spontaneous.

Option E: ATP is acting as a transport protein to facilitate the movement of the ion across the plasma membrane is false because ATP is not a protein, rather it serves to activate the transport protein by phosphorylating it.