Chemical element with atomic number 15
Phosphorus (P) is an essential mineral that exists in all living cells of both animals and plants, including humans. In the human body, phosphorus accounts for about 1% of body mass, excluding fat, with 85% of it being found in bones and teeth, while the remaining 15% is distributed in blood and soft tissues. [1] Phosphorus, which has an atomic number of 15, has 8 electrons in its filled inner shell and 5 electrons in its outer shell, allowing it to form 5 covalent bonds by donating these electrons. Due to its high reactivity, pure phosphorus rarely exists in nature, and it typically exists in biological systems as phosphoric acid (H3PO4). In aqueous solution, it loses all three protons (H+) and becomes ionized, forming phosphate, which is represented by the phosphate group ([PO4]3−) commonly seen in biochemistry. This occurs because protons are typically removed at physiological pH (pH 7, neutral). Phosphorus that is not bonded to carbon-based organic molecules is referred to as inorganic phosphate, usually denoted as Pi. Phosphates are soluble in water and carry a negative charge.
Phosphorus has a variety of allotropes, which are forms that differ in their atomic arrangement, leading to diverse properties and appearances. These include white phosphorus (or yellow phosphorus), red phosphorus, black phosphorus, and violet phosphorus. White phosphorus is the most reactive, highly flammable, and toxic; it ignites spontaneously upon contact with oxygen, producing light as it burns until the oxygen is depleted. Due to its lethal flammability, white phosphorus has been used to produce the terrifying chemical weapon known as "white phosphorus munitions." Red phosphorus is the red part of match heads. The name "phosphorus" is derived from the Greek words "phos," meaning light, and "phoros," meaning to carry, conveying the idea of a substance that emits light.
Looking into the history of phosphorus discovery, it is said that a German alchemist accidentally discovered it while experimenting in search of the philosopher's stone that could turn base metals into gold. He heated large amounts of his own urine, and as a result, a white powder was left behind, which was phosphorus. This is notable because phosphorus is excreted through urine, highlighting the wisdom of utilizing human and animal urine for agriculture long before the advent of synthetic fertilizers, which contain the essential three elements for plant growth: nitrogen (N), phosphorus (P), and potassium (K).
What roles does phosphorus play in the human body?
Phosphorus is often said to be a key element essential for sustaining life. Why is that? By examining the actual roles that phosphates play in the human body, one can fully appreciate their importance.
1. It forms the backbone that supports the structure of DNA and RNA.
All genetic information for proteins is encoded within the structure of DNA, and RNA copies the necessary genetic information from DNA to send to the ribosome for specific protein synthesis. The outer helical framework that supports the structure of DNA and RNA is formed by the connection of phosphates and pentoses. We will look at the details of this connection later.
2. It generates and stores energy.
It is well known that ATP is the energy storage medium used by the human body. Adenosine is formed by combining the nitrogen base adenine with the pentose sugar ribose, and when three phosphate groups are attached to this, it becomes ATP (Adenosine tri-phosphate), as the name suggests. ATP is a high-energy phosphate bond, as it takes a lot of energy to maintain this state where three negatively charged phosphate groups are forcibly attached to it. If even one of the three phosphate groups is removed in a state similar to a spring being forcibly pressed by the force that repels the same poles, a tremendous amount of energy will be released in the process, and this is the principle by which the human body utilizes this energy. In order to use this energy, we continuously synthesize ATP through a process called cellular respiration in factories called mitochondria. Because this process absolutely requires oxygen, the process of ATP production is also called 'cellular respiration'. If we are unable to breathe for any reason, we will lose life because we will not be able to produce ATP.
It is well known that ATP is the energy storage molecule used by the human body. Adenosine is formed when the nitrogenous base adenine combines with the pentose ribose, and when three phosphate groups are attached to it, it becomes ATP (Adenosine tri-phosphate). ATP is a high-energy phosphate bond, as it takes a lot of energy to maintain this state,where ATP holds three negatively charged phosphate groups together. The repulsive force between like charges is suppressed, creating a state similar to a compressed spring; if even one of the three phosphate groups is removed, an enormous amount of energy is released in the process. This is the principle by which the body utilizes energy. To harness this energy, we continuously synthesize ATP through the process of cellular respiration in the mitochondria. Since this process requires oxygen, the ATP production process is also referred to as "cellular respiration." If for any reason we are unable to breathe, we cannot produce ATP, leading to the loss of life.
3. It forms metabolic intermediates involved in metabolic processes.
Phosphates are also involved in the metabolism of carbohydrates and lipids. Some representative intermediates include glucose-6-phosphate (G6P), which is the first step in the glycolysis process that breaks down glucose; dihydroxyacetone phosphate (DHAP), which is one of the intermediate steps in the breakdown of glucose itto pyruvate; and phosphoenolpyruvate (PEP), which is the final precursor in this pathway. Examining glycolysis reveals that phosphates appear in numerous steps throughout the process.
4. It forms coenzymes and cofactors.
Phosphorus is essential for the production of various coenzymes that are absolutely necessary for enzymes to function properly. Some of the most important coenzymes in human biochemical processes include NAD+, FAD, NADP, coenzyme A (CoA), and thiamine pyrophosphate, so important that just hearing their names is enough to recognize them.
5. It is a mechanism that regulates and controls the biochemical process of protein phosphorylation.
In the process of protein synthesis, RNA copies genetic information from DNA and sends it to the ribosomes, the factories for protein production. Afterward, proteins undergo a process called folding to acquire their three-dimensional shapes, which define their functions. However, there are ways to adjust and control proteins that have already completed the synthesis process, and one of them is a process called phosphorylation. This powerful mechanism can activate or inhibit proteins within various cellular processes, much like turning a switch on or off. In fact, the reason I wrote this article was to gain a detailed understanding of the phosphorylation process. We will explore this in more detail later.
6. It is a component of cell membrane phospholipids.
I have already expressed admiration for the unique structure and function of cell membranes several times. The reason that cells, which are mostly composed of water in their cytoplasm, can form a clear and distinct boundary with the aqueous environment outside is due to their lipid bilayer structure. This thin cell membrane allows cells to maintain their unique identity and function separate from the outside. In this context, the head portion of the phospholipid is composed of a polar phosphate group, which interacts well with the polar aqueous environment without conflict.
Cell membrane phospholipids come in various types. For reference, in the illustration above, the hydrophobic head of the cell membrane phospholipid is simply represented as a phosphate group, but in reality, it is common for other molecules to be attached to this phosphate. The most typical form is when choline is attached to the phosphate, which is called phosphatidylcholine (PC). It is also necessary to pay attention to the cell membrane phospholipid phosphatidylinositol (PI), which exists in very small amounts in the cell membrane but plays a very important role as a second messenger in the intracellular signaling system. It is a form in which an inositol sugar is bound to phosphate, and will be discussed again in the signaling pathway in the future.
[References]
[1] Phosphorus
https://ods.od.nih.gov/factsheets/Phosphorus-HealthProfessional/
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