Adenosine Triphosphate (ATP)
- Living cells acquire energy by the breakdown of complex molecules such as polysaccharides, fats, proteins, alcohols etc.
- Phototrophs utilizes sunlight as the source of energy whereas chemotrops utilizes the chemical compounds as the source of energy.
- By the degradation of complex molecules a lot of energy is released which is captured in the cell in the form of chemical bonds that can be utilized readily when needed.
- The rest of the energy which is not captured in lost as heat.
- In the cell, the energy is captured in the form of adenosine triphosphate (ATP)
- ATP is nucleotide and it consists of adenine, pentose sugar ribose and a triphosphate unit.
Fig: Adenosine Triphosphate (ATP)
- The ATP is activated by cations such as Mg 2+ and Mn2+. ATP is complexed with these cations and activated.
- The energy is stored in its triphosphate moiety.
- Heterotrophic cells obtain free energy in chemical form by the catabolism of nutrient molecules and they use that energy to make ATP from ADP and Pi.
- The ATP thus formed, undergoes hydrolysis to ADP and Pi and release energy which is utilized for various purposes.
- Sometimes, ATP is hydrolysed to AMP and pyrophosphate(PP).
Role of ATP in the cell
- ATP plays a major role in anabolic reactions such as the synthesis of macromolecules from simple precursors. In the process, the terminal phosphate group or groups of ATP are transferred enzymatically to precursor building block molecules which thus become energized and prepared for their assembly into macromolecules.
- The performance of mechanical work in muscle contraction and other cellular movements also require ATP.
- The active transport of molecules and ions through membranes against the concentration gradient is only possible by the involvement of ATP i.e. ABC transport system (ATP binding cassette).
Fig: ATP binding cassette
- ATP is required for the biosynthesis of DNA [ DNA replication → DNA topoisomerase II or DNA gyrase of prokaryotes require ATP].
- It is also required for the synthesis of protein (during activation of amino acids).
Fig: Activation of amino acids