Adenosine diphosphate

A nucleotide involved in energy transfer and metabolism

Adenosine diphosphate (ADP) is an important organic compound in metabolism and is essential to the flow of energy in living cells. ADP consists of three components: a sugar backbone attached to adenine and two phosphate groups bonded to the 5' carbon atom of ribose. It plays a critical role in cellular energy transfer and is involved in various biochemical processes.

Structure

ADP is composed of the nucleoside adenosine and two phosphate groups. The adenosine component consists of the adenine base attached to a ribose sugar. The two phosphate groups are connected by high-energy bonds, which are crucial for the molecule's role in energy transfer.

Function

ADP is primarily involved in the transfer of energy within cells. It is a product of adenosine triphosphate (ATP) dephosphorylation by ATPase enzymes. When ATP is hydrolyzed, it releases energy and converts into ADP and an inorganic phosphate (Pi). This reaction is reversible, allowing ADP to be converted back into ATP through phosphorylation, a process that occurs in the mitochondria during cellular respiration.

Role in Metabolism

ADP plays a central role in metabolism, particularly in the processes of glycolysis, the citric acid cycle, and oxidative phosphorylation. During glycolysis, glucose is broken down, and ADP is phosphorylated to form ATP. In the citric acid cycle, ADP is again phosphorylated to ATP, providing energy for various cellular activities.

Energy Transfer

The conversion of ADP to ATP is a key mechanism of energy transfer in cells. This process is facilitated by the enzyme ATP synthase, which is located in the inner mitochondrial membrane. The energy required for this conversion is derived from the proton gradient established across the membrane during electron transport.

Biological Significance

ADP is not only crucial for energy transfer but also plays a role in signal transduction and platelet activation. In signal transduction, ADP acts as a signaling molecule that can activate various pathways. In the context of platelet activation, ADP is released from activated platelets and contributes to the aggregation of platelets, a critical step in the formation of blood clots.

Gallery

• 

  Adenosine diphosphate structure

• 

  3D model of adenosine diphosphate

• 

  Conversion between ATP and ADP

• 

  Overview of glycolysis

• 

  ATP synthase mechanism

Related pages

• Adenosine triphosphate
• Cellular respiration
• Glycolysis
• Citric acid cycle
• Oxidative phosphorylation