ADP (ADENOSINE DIPHOSPHATE): CHARACTERISTICS, STRUCTURE AND FUNCTIONS - GEOGRAFÍA - 2024

The adenosine diphosphate, abbreviated as ADP, is a molecule formed by one anchored to an adenine ribose phosphates and two groups. This compound is of vital importance in metabolism and in the flow of energy in cells.

ADP is in constant conversion to ATP, adenosine triphosphate and AMP, adenosine monophosphate. These molecules only vary in the number of phosphate groups they possess and are necessary for many of the reactions that occur in the metabolism of living beings.

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ADP is a product of a large number of metabolic reactions carried out by cells. The energy required for these reactions is provided by ATP, and by breaking it down to generate energy and ADP.

In addition to its function as a necessary building block for the formation of ATP, ADP has also been shown to be an important component in the blood clotting process. It is capable of activating a series of receptors that modulate the activity of platelets and other factors related to coagulation and thrombosis.

Characteristics and structure

The structure of ADP is identical to that of ATP, only it lacks a phosphate group. It has a molecular formula of C ₁₀ H ₁₅ N ₅ O ₁₀ P ₂ and a molecular weight of 427.201 g / mol.

It is made up of a sugar skeleton attached to a nitrogenous base, adenine, and to two phosphate groups. The sugar that forms this compound is called ribose. Adenosine is linked to sugar at its carbon 1, while phosphate groups do so at carbon 5. We will now describe each component of ADP in detail:

Adenine

Of the five nitrogenous bases that exist in nature, adenine - or 6-amino purine - is one of them. It is a derivative of purine bases, which is why it is often referred to as purine. It is made up of two rings.

Ribose

Ribose is a sugar with five carbon atoms (it is a pentose) whose molecular formula is C ₅ H ₁₀ O ₅ and a molecular mass of 150 g / mol. In one of its cyclic forms, β-D-ribofuranose, it forms the structural component of ADP. It is also the case for ATP and nucleic acids (DNA and RNA).

Phosphate groups

Phosphate groups are polyatomic ions formed by a phosphorous atom located in the center and surrounded by four oxygen atoms.

Phosphate groups are named in Greek letters depending on their closeness to ribose: the closest is the alpha (α) phosphate group, while the next is the beta (β). In ATP we have a third phosphate group, gamma (γ). The latter is the one that is cleaved in ATP to yield ADP.

The bonds that join phosphate groups are called phosphoanhydrics and are considered high-energy bonds. This means that when they break they release an appreciable amount of energy.

Features

Building block for ATP

How are ADP and ATP related?

As we mentioned, ATP and ADP are very similar at the structural level, but we do not clarify how both molecules are related in cellular metabolism.

We can imagine ATP as the "energy currency of the cell". It is used by numerous reactions that occur throughout our lives.

For example, when ATP transfers its energy to the protein myosin - an important component of muscle fibers, it causes a change in muscle fiber conformation that allows muscle contraction.

Many of the metabolic reactions are not energetically favorable, so the energy bill must be "paid" by another reaction: the hydrolysis of ATP.

Phosphate groups are negatively charged molecules. Three of these are bound together in ATP, leading to high electrostatic repulsion between the three groups. This phenomenon serves as energy storage, which can be released and transferred to biologically relevant reactions.

ATP is analogous to a fully charged battery, the cells use it and the result is a “half charged” battery. The latter, in our analogy, is equivalent to ADP. In other words, ADP provides the raw material necessary for the generation of ATP.

ADP and ATP cycle

As with most chemical reactions, the hydrolysis of ATP into ADP is a reversible phenomenon. That is, the ADP can "recharge" - continuing our battery analogy. The opposite reaction, which involves the production of ATP from ADP and an inorganic phosphate, requires energy.

There must be a constant cycle between the ADP and ATP molecules, through a thermodynamic process of energy transfer, from one source to the other.

ATP is hydrolyzed by the action of a water molecule and produces ADP and an inorganic phosphate as products. In this reaction energy is released. The breaking of the phosphate bonds of ATP releases about 30.5 kilojules per mole of ATP, and the subsequent release of ADP.

Role of ADP in coagulation and thrombosis

ADP is a molecule with a vital role in hemostasis and thrombosis. It has become clear that ADP is involved in hemostasis since it is responsible for the activation of platelets through receptors called P2Y1, P2Y12 and P2X1.

The P2Y1 receptor is a G-protein coupled system and is involved in platelet shape change, platelet aggregation, procoagulant activity, and fibrinogen adhesion and immobilization.

The second receptor that modulates ATP is P2Y12, and it appears to be involved in similar functions to the receptor described above. In addition, the receptor also activates platelets through other antagonists, such as collagen. The last receiver is P2X1. Structurally, it is an ion channel that is activated and causes the flow of calcium.

Thanks to the knowledge of how this receptor works, drugs have been developed that affect its functioning, being effective for the treatment of thrombosis. This last term refers to the formation of clots inside the vessels.

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