ATP

ATP (adenine triphosphate)

ATP is a nucleoside triphosphate used in cells, often called the "molecular unit of currency" of intracellular energy transfer. It belongs to a category of high energy compounds that release energy when the bond between the second and third phosphate is broken. The presence of these high energy bonds makes it possible for ATP to store and release energy for cellular reactions.

Its structure:

ATP is an energy store, because the last phosphate bonds are highly energetic when broken.

The hydrolysis of ATP to ADP is catalyzed by the enzyme ATPase and the removal of the terminal phosphate yields 30.6 kJ/mol of free energy. The second hydrolysis (ADP to AMP) also releases energy. AMP and ADP may be re-converted to ATP by the addition of phosphate molecules in a process called phosphorylation of which there are two main forms.

• Photophosphorylation – occurring during photosynthesis in chlorophyll-containing cells.
• Oxidative phosphorylation – occurring during cellular respiration in all aerobic cells.

Uses of ATP

1. Muscle contraction ATP provides the energy required for muscle fibers to slide past each other during contraction.
2. Active transport ATP powers the movement of substances against their concentration gradients across cell membranes.
3. Nerve impulse transmission ATP is used in the active transport of ions (e.g., sodium and potassium) necessary for generating and propagating nerve impulses.
4. Protein synthesis ATP supplies energy for the formation of peptide bonds during translation in ribosomes.
5. DNA replication ATP is required for the unwinding of DNA strands and the synthesis of new DNA strands.
6. Cell division ATP fuels processes like chromosome separation and formation of the spindle apparatus.
7. Photosynthesis In plants, ATP generated in the light-dependent reactions is used in the Calvin cycle to fix carbon.
8. Cellular respiration While respiration produces ATP, some is also used to regulate enzymatic steps in the process.

Examples

1. Energy Currency: Cellular processes like muscle contraction and active transport.
2. Phosphorylation: Activation of proteins and enzymes.
3. Signal Transduction: cAMP production in cell signaling pathways.
4. Metabolic Pathways: Glycolysis, Krebs cycle, and oxidative phosphorylation.
5. Synthesis: DNA and RNA synthesis.