Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 8.3 ATP Powers Cellular Work by Coupling Exergonic Reactions to Endergonic Reactions
Adenosine triphosphate (ATP) is the primary energy currency of the cell, enabling the performance of various types of work by coupling energy-releasing processes to energy-consuming ones.
1. The Structure and Hydrolysis of ATP
Structure: ATP consists of the sugar ribose, the nitrogenous base adenine, and a chain of three phosphate groups.
Hydrolysis: The bonds between ATP's phosphate groups can be broken by hydrolysis, releasing energy:
ATP + H₂O → ADP + Pᵢ + Energy
This reaction releases approximately 7.3 kcal/mol under standard conditions.
2. How ATP Performs Work
Energy Coupling: ATP hydrolysis is used to drive endergonic reactions by transferring a phosphate group to another molecule, creating a phosphorylated intermediate.
Types of Cellular Work:
Chemical Work: Driving endergonic reactions such as the synthesis of macromolecules.
Transport Work: Pumping substances across membranes against their concentration gradients.
Mechanical Work: Facilitating processes like muscle contraction and movement of chromosomes during cell division.
3. The Regeneration of ATP
ATP Cycle: ATP is regenerated by the addition of a phosphate group to adenosine diphosphate (ADP):
ADP + Pᵢ + Energy → ATP + H₂O
This process is endergonic and requires energy derived from exergonic reactions, such as cellular respiration.
In a Nutshell
ATP serves as the main energy currency in cells, powering various types of work by coupling exergonic and endergonic reactions.
The continuous regeneration of ATP from ADP ensures a steady supply of energy to sustain cellular functions.