Main Difference – ADP vs ATP
ATP and ADP are molecules containing a great amount of stored chemical energy. The Adenosine group of ADP and ATP is composed of Adenine although they also contain phosphate groups. Chemically, ATP stands for Adenosine Tri Phosphate and ADP stands for Adenosine Di Phosphate. The third phosphate of ATP is attached to the other two phosphate groups with a very high energy bond, and a large amount of energy is released when that phosphate bond is broken. ADP results in the removal of the third phosphate group from ATP. This is the key difference between ATP and ADP. However, compared to ATP, ADP molecule has much less chemical energy, because the high-energy bond between the last 2 phosphates has been broken. Based on the molecular structure of ATP and ADP, they have their own of ADP. In this article, let’s elaborate what are the differences between ATP and ADP.
What is Adenosine Tri Phosphate (ATP)
Adenosine triphosphate (ATP) is used by biological creatures as a coenzyme of intracellular chemical energy transfer within cells for metabolism. In other words, it is the main energy carrier molecule used in living things. ATP is generated as a result of photophosphorylation, aerobic respiration, and fermentation in biological systems, which facilitates the accumulation of a phosphate group to an ADP molecule. It consists of adenosine, which is composed of an adenine ring and a ribose sugar and three phosphate groups also known as triphosphate. Biosynthesis of ADP as a result of,
Glucose + 2NAD+ + 2 Pi + 2 ADP = 2 pyruvate + 2 ATP + 2 NADH + 2 H2O
Glucose = 2CH3CH(OH)COOH + 2 ATP
What is Adenosine Di Phosphate (ADP)
ADP consists of adenosine which is composed of an adenine ring and a ribose sugar and two phosphate groups also known as diphosphate. This is vital to the flow of energy in biological systems. It is generated as a result of de-phosphorylation of ATP molecule by enzymes known as ATPases. The breakdown of a phosphate group from ATP results in the release of energy to metabolic reactions. IUPAC name of ADP is [(2R,3S,4R,5R)-5-(6-aminopurin-9-yl)-3,4-dihydroxyoxolan-2-yl]methyl phosphono hydrogen phosphate. ADP is also known as adenosine 5′-diphosphate.
Difference Between ADP and ATP
ATP and ADP may have significantly different physical and functional characteristics. These can be categorized into following subgroups,
ATP: Adenosine Triphosphate
ADP: Adenosine Di Phosphate
ATP: ATP consists of adenosine (an adenine ring and a ribose sugar) and three phosphate groups (triphosphate).
ADP: ADP consists of adenosine (an adenine ring and a ribose sugar) and two phosphate groups.
Number of Phosphates Groups
ATP: ATP has three phosphate groups.
ADP: ADP has two phosphate groups.
ATP: Its chemical formula is C10H16N5O13P3.
ADP: Its chemical formula is C10H15N5O10P2.
ATP: The molar mass is 507.18 g/mol.
ADP: The molar mass is 427.201 g/mol.
ATP: The density of ATP is 1.04 g/cm3.
ADP: The density of ADP is 2.49 g/mL.
Energy State of Molecule
ATP: ATP is a high-energy molecule compared to ADP.
ADP: ADP is a low energy molecule compared to ATP.
Energy Releasing Mechanism
ATP: ATP + H2O → ADP + Pi ΔG˚ = −30.5 kJ/mol (−7.3 kcal/mol)
ADP: ADP + H2O → AMP + PPi
Functions in Biological System
- Metabolism in cells
- Amino acid activation
- Synthesis of macromolecules such as DNA, RNA, and protein
- Active transport of molecules
- Maintaining cell structure
- Contribute to cell signalling
- Catabolic pathways such as glycolysis, citric acid cycle and oxidative phosphorylation
- Blood platelet activation
- Play a role in mitochondrial ATP synthase complex
In conclusion, ATP and ADP molecules are types of “universal power source” and the key difference between them is the number of phosphate group and energy content. As a result, they may have substantially different physical properties and different biochemical roles in the human body. Both ATP and ADP are involved in the important biochemical reactions in the human body and thus they are considered as vital biological molecules.
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“Adenosine-diphosphate-3D-balls” By Jynto (talk) – Own work This chemical image was created with Discovery Studio Visualizer. (CC0) via Commons Wikimedia
“ATP-xtal-3D-balls” By Ben Mills – Own work (Public Domain) via Commons Wikimedia
“Adenosindiphosphat protoniert” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
“Adenosintriphosphat protonier” By NEUROtiker – Own work, (Public Domain) via Commons Wikimedia