Properties and biological functions of water PDF

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Properties and biological fuctions of water...

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Properties and biological functions of water

Summary Water is a substance of capital importance for life with exceptional properties due to its composition and structure. It is a simple molecule made up of three small atoms, one oxygen and two hydrogen, with polar bonds that allow hydrogen bonds to be established between adjacent molecules. This bond is of great importance because it gives water properties that correspond to a higher molecular mass. Hence its high melting and boiling points, essential for water to be in a liquid state at Earth temperature. Its high specific heat makes it an exceptional buffer and regulator of thermal changes, keeping body temperature constant. The high value of the heat of vaporization allows to eliminate, by means of sweat, large amounts of heat preserving us from "heat stroke". Another property that makes this molecule unique is its wide capacity as a solvent for polar substances. Taking into account that we are mostly water, almost all of the chemical reactions produced within us are carried out in an aqueous medium. Nutrient and metabolite transport and excretion of waste substances also takes place through water.

Introduction Water, an extremely simple compound, is nevertheless a substance with such exceptional and unique characteristics that without it life would be impossible. Man needs water to carry out his vital functions, to prepare and cook food, for hygiene and domestic uses, to irrigate the fields, for industry, for power plants: in short, to live. In man, water is the liquid in which the life process takes place and, in fact, the survival of cells depends on their ability to maintain cell volume and homeostasis. It is fundamental for practically all the functions of the organism and is also its most abundant component. However, although we depend on it, our body is not able to synthesize it in sufficient quantities or store it, so it must be ingested regularly. Therefore, water is a true nutrient that must be part of the diet in much greater amounts than any other nutrient. There are organisms capable of living without light, even without oxygen, but none can live without water. As Hildreth Brian wrote, "A man can live days without eating, but only 2-5 days without water." We can lose almost all the fat and almost half of the protein in our body and we are still alive, but the loss of only 1-2% of the body water affects thermoregulation and the cardiovascular and respiratory systems and greatly limits physical capacity. and mental; increased hypohydration can have fatal consequences. In addition, we must not lose sight of the fact that in nature there is never found the water of chemicals, that is, pure, odorless, colorless and tasteless water. River water, groundwater, rainwater and the water we drink always contain other dissolved substances that, even in small quantities, provide organoleptic and nutritional qualities, so water should also be considered a food, a component more of our diet, a fundamental ingredient in the kitchen, Knowing the dependence that living beings have on water and the importance it has had in the History of Humanity, it is worth asking what makes it such a special substance and so different from others. The secret of its exceptional characteristics lies precisely in its composition and structure, which give it the greatest number of anomalous physical and chemical properties among common substances, and this personality is responsible for its essentiality in homeostasis, structure and function of cells. and body tissues. When compared to molecules of similar molecular weight and composition, water has unique physical properties, a consequence of its polar nature and its ability to form hydrogen bond bonds with other molecules.

Composition and structure Water is a simple molecule made up of small atoms, two hydrogen and one oxygen, linked by very strong covalent bonds that make the molecule very stable. It has an irregular distribution of electronic density, since oxygen, one of the most electronegative elements, attracts to itself the electrons of both covalent bonds, so

that the highest electron density (negative charge) is concentrated around the oxygen atom and near of hydrogens the least (positive charge). The molecule has an angular geometry (the two hydrogen atoms form an angle of about 105º), which makes it a polar molecule that can join many other polar substances.

The electrostatic attraction between the positive partial charge near the hydrogen atoms of one water molecule and the negative partial charge near the oxygen of another, allows the union of neighboring water molecules by means of a very special chemical bond and of exceptional importance for the life and that explains the wide range of its physical and chemical properties: the hydrogen bridge. Bonding only requires that the electronegative atom (oxygen in the case of water) that attracts hydrogen be small, possess a pair of non-bonding electrons, and a geometry that allows hydrogen to bridge the two electronegative atoms. Each water molecule can potentially form 4 hydrogen bonds with as many water molecules, giving rise to a relatively ordered reticular tetrahedral structure, responsible for its peculiar physical-chemical properties. This attraction is strong because the water molecules, being small, can get much closer than larger molecules and are firmly attracted by their great polarity. The energy of a waterwater hydrogen bridge is about 5.5 kcal / mol; in addition, the Van Der Waals interactions between nearby molecules must be taken into account. Consequently, it is difficult for them to separate and thus prevents them from escaping as steam. This makes the water have a great intermolecular cohesiveness, conditioning its

high boiling point, melting point and high specific heat. Breaking these bridges, which are many in a body of water, requires a lot of energy and therefore the water has such a high boiling point. This is the reason why water is liquid in the wide range of temperatures in which life's reactions take place and not a gas as it would be due to its low molecular weight. The boiling point of a compound is a function of its molecular mass. The water would have a boiling point of about -100ºC (173K) (dotted red line) and, therefore, we would not find liquid water in nature, only in a gaseous state. However, the boiling temperature of H2O is + 100ºC (373K). The explanation for this apparently anomalous value lies in the fact that water molecules, thanks to hydrogen bonds, attract so strongly that they do not behave as isolated molecules but as much larger molecules, so that they have a molecular mass apparent higher. The transitory nature of hydrogen bridges, which are continually forming and breaking, allows the mobility of molecules, contributing to the water being liquid at room temperature. Hydrogen bridges are essential for life as they not only confer structural resistance to water but also to many other molecules. For example, they play a crucial role in the structure of DNA, binding the nitrogenous bases and, in proteins, allow the reversible changes that make their functions possible.

Physical and chemical characteristics. Biological functions This unique composition and structure gives the water some very important physical and chemical characteristics in its biological functions, especially those related to its solvent, transport, structural and thermoregulatory capacity.

Remember that the functions of biological systems can always be explained in terms of physical and chemical processes. The thermal behavior of water is unique and thanks to this, water is the main responsible for the body's thermoregulatory system, keeping body temperature constant, regardless of the environment and metabolic activity. This is one of its most important functions. It has a high thermal conductivity that allows rapid and regular distribution of body heat, avoiding temperature gradients between different areas of the body and favoring heat transfer to the skin to be evaporated. Its high specific heat [1 kcal / kg ºC = 4180 J / kg · K], a consequence of the great capacity to store energy in hydrogen bridges, makes it an exceptional buffer and regulator of thermal changes. Although it accepts or transfers a large amount of heat, its temperature changes very little, thanks to its great capacity to store heat. Man's metabolic apparatus for the digestion and processing of nutrients and for muscular contraction is highly endergonic, releasing large amounts of heat that must be dissipated to maintain homeothermia. For example, the thermogenic effect of food digestion is 10-15% of the caloric content of a mixed diet. Muscle contraction is even a major contributor to the body's heat load, as the transformation of chemical energy (ATP) into mechanical energy is very ineffective, releasing 70-75% of energy as heat (11). Thus, during exercise, when the need to use mechanical energy increases, the heat production is also greater. In these cases, to prevent a dangerous increase in temperature, Water absorbs heat wherever it is generated and dissipates it in the body's liquid compartments, minimizing the risk of localized heat damage to enzymes or protein structures. Hence the importance of the large amount of water in the body and also that this amount does not decrease below certain limits. Its thermoregulatory function is also related to another of its physical characteristics that gives it its cooling effect: its high heat of vaporization [at 25ºC is 540 kcal / L], a consequence of the attraction between adjacent water molecules (strength of the bridges of hydrogen) that give liquid water a great internal cohesion. Water, to evaporate, absorbs more heat than any other substance. For every liter of sweat or respiratory water that the body vaporizes, about 540 kcal of body heat dissipates, achieving effective cooling. Thus, in the face of an extra load of heat, it dissipates by evaporating relatively small amounts of water, protecting us from dehydration. It is important to note that although sweat is a very effective way to remove heat, it can lead, when prolonged, to to excessive water loss that, if not replaced, can cause serious problems. In fact, the body needs to balance losses by ingesting liquids in order to continue maintaining the ability to regulate body temperature. When sweat losses dangerously exceed intake, the circulatory system is unable to cope with the situation and blood flow to the skin is reduced. This results in less sweating and therefore less ability to lose heat. Under these conditions there is an increase in body temperature that can have fatal consequences. the body needs to balance losses by ingesting liquids in order to

continue maintaining the ability to regulate body temperature. When sweat losses dangerously exceed intake, the circulatory system is unable to cope with the situation and blood flow to the skin is reduced. This results in less sweating and therefore less ability to lose heat. Under these conditions there is an increase in body temperature that can have fatal consequences. the body needs to balance losses by ingesting liquids in order to continue maintaining the ability to regulate body temperature. When sweat losses dangerously exceed intake, the circulatory system is unable to cope with the situation and blood flow to the skin is reduced. This results in less sweating and therefore less ability to lose heat. Under these conditions there is an increase in body temperature that can have fatal consequences.

Water has a high surface tension value, leaving the surface molecules strongly attracted, although some substances can break this attraction. This is the case of soap that foams or bile salts that facilitate the digestion of fats. The emulsified fat droplets are then organized into micelles that increase absorption (create a greater diffusion gradient) and facilitate the entry of other nutrients. In the intestine, fat droplets are observed in the form of an emulsion, but also as micelles, much larger in size than the emulsified droplets and always in greater quantity, which bring the lipids that transport the enterocyte closer to being absorbed. In this way, bile salts improve digestibility and also the absorption of fat and other nutrients.

It also has exceptional and unique solvent properties. Due to its small size, the polar nature of its H - O bonds, its angular structure, and its ability to form hydrogen bonds, water is a highly reactive molecule that can dissolve a wide variety of ionic (hydrophilic) substances and molecular, but also prevents the dissolution of other apolar (hydrophobic), an effect that is also very important for life. The body is essentially an aqueous solution in which a large amount of solutes (proteins, vitamins, glucose, urea, sodium, chlorine, potassium, O2, CO2, etc.) are distributed in the different compartments. Thanks to its solvent capacity, its high dielectric constant and its low degree of ionization (Kw = 10–14), water is the medium in which all metabolic reactions take place, participating in many of them as substrate or as product. An example is the hydrolysis reactions that occur in the digestion or oxidation of macronutrients (12). In ionic solutions, the high heat of hydration (energy that is released when the ions are surrounded by water molecules), provides great stability to the solution. Furthermore, due to its high dielectric constant (K = 80 at 20ºC), ionic solutions conduct the electric current; hence its importance, for example, in nerve transmission.

The importance of water for human beings The importance of water for the human being is evident as the percentage of water in our body almost reaches two thirds. It is present in body tissues and in vital organs. It is a fundamental element for vital bodily processes. Without drinking water, we could not survive beyond three or four days. It is essential for the development of organic processes such as digestion, as well as for the absorption and elimination of waste. It structures the circulatory system and distributes nutrients to the entire body through the blood. Other benefits of water for our body include maintaining somatic temperature by eliminating excess heat with its exit in the form of perspiration and steam through the skin, relieving fatigue, avoiding headaches or reducing the risks of heart problems. On the other hand, the importance of water is also found in the activities carried out by the human being. Thus, it is used for agriculture in 70%, in 15% in industry and the other 15% for domestic use. The importance of water in all living things is crucial. It is an element of nature that integrates natural ecosystems and is fundamental for the maintenance and survival of life throughout the planet. Without water, it would not be possible for the biological processes necessary for the reproduction of life to take place.

Water is the most abundant component in organic media and, on average, all living things are 70%. It is not just about the need to drink, to hydrate, but the water is regulating the terrestrial ecosystems, maintaining a necessary balance for animal and plant subsistence. Without in the water, the stability of the functioning between living beings and their environment would be weakened....