The major energy L.:rrency of all cells is adenosine triphosphate (ATP). ATP plays a central ro:(.. ( energy currency in all organisms. So it appeared early in
the iNstor. .M ife e ability of ATP to store and release energy depends on the
uct.irr. ..f ATP. Each ATP molecule has three subunits:
. yarmic molecule composed of two carbon-nitrogen rings.
ox .hate groups in a linear chain.
Viecnao;srn of energy transfer by ATP
The covalent bond connects these phosphates. These bonds are high energy ind However, the energy is not localized in the bond. It spreads in the
e n– olecule. This energy is released as the phosphate bond breaks.
:1,-re Lands have low activation energy and break easily. The breaking of cr! releases about 7.3 kcal (7,300 calories) per mole of ATP.
ATP + 11,0 —> ADP P1 + energy (7.3 kcil/mole)
- lergy from ATP is used to drive endergonic reactions of the cells. The
- -1 L„—une, k. In‘wirnlocic Nnw ATPbecomes ADP (adenosine diphosphate). In some cases, ADP is hydrotyzed to AMP (adenosine monophosphate) as follows:
ADP + H20 AMP + Pi + energy (7.3 kcal/mole)
- Cells contain a reservoir of ADP and phosphate (Pi). ATP is constantly broken into ADP and phosphate. It drives many energy-requiring processes of the cells. It enables the animal to perform biological work. However, ATP cannot be stored for long time. ATP lasts only a few seconds before it is used to perform biological work. Thus, cells constantly recycle ADP.
- The cell removes energy from foodstuffs, stored fa li and starch. As a result the ADP and phosphate, recombine to form ATP. Thus 7.3 kcal of energy per mole is stored to each newly formed high-energy phosphate bond.
- Functions of ATP
ATP performs three functions in the cell:
- Mechanical work: It performs mechanical work like beating of cilia the ontraction of muscles, and the flow of cytoplasm within the cell and moveraent of chromosomes during cellular reproduction.
- Transport work: The pumping of substance across membrane against the dir.-ction of movement, i.e. Active transport.
- Chemical work: Supply of energy in endergonic energy. These reactions cannot proceed without energy.