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Encyclopedia about Chemistry

 

Proteins, fats and sugars

All living organisms need foodstuffs to continue living, or to continue their lives and keep surviving, thriving and in some cases, growing.

Proteins, fats and sugars are all of nutritional value to living organisms. All three have a great significance as the donors of building materials and providers of energy for both plants and animals.

All three are organic molecules, and they can all three be found as constituents of the foods that are derived from both plant and animal matter.

Sugars are most often found in nature in foodstuffs, those substances which are ingested. They take part in the synthesis of both DNA and RNA. Sugars can be divided into two groups: the simple sugars (monosaccharides) and more complex sugars (polysaccharides), which are composed of multiple units of monosaccharides.

Fats are energetically the most concentrated of all sustenance materials. They are found in both plant and animal organisms, serving these living organisms as a source of energy. Thanks to their chemical structure, they can provide organisms with the greatest amount of energy possible from the least amount of matter. Because most animals, including humans, need to keep a store of energy for times when it is needed, it is clear that these stores of fat cannot be shed at any time when an organism deems it so necessary. In other words, an organism cannot rid itself of fat just because it wants to. This explains why it is so difficult to lose unwanted weight, or fat. Fats are composed of tertiary alcohols. Plant fats are naturally-occurring liquids, with viscous qualities. Animal fats are, of course, solids at room temperature.

Proteins are composed of long chains of amino acids. Amino acids are molecules which are composed of one amino group and one carboxylic group. Proteins can be composed of more than 200 amino acids. Most of these are water soluble. Organic compounds contain a great number of proteins, so that living organisms are constantly, if only gradually, assimilating materials from outside their bodies. Proteins are one of these ingested substances. Of course, some of the substances ingested can be harmful. Among these are the heavy metals, including lead. It is also important for organisms to be wary of high temperatures (body temperature higher than 42° C is very dangerous for living organisms - excessive temperature). Another danger is organic solvents such as benzene, which can damage living systems and can destroy them completely if the concentration introduced is excessive.

Significance

Sugars, proteins and fats are extremely important, especially for the lives of human beings.

As chemical raw materials, fats serve in the production of basic cleaning materials and are an important component in many cosmetics. The significance of sugars as a chemical industry raw material is growing, because they are raw materials which are very easy to grow.

Cellulose is an irreplacable raw material in the production of paper. It is also used in the production of chemical fibres (viscoses).

Starches are finding ever greater uses in the production of artificial fibres and plastics, for example as thermoplastics.

Raw sugar is used in the production of alcohol which is finding use as an environmental motor fuel.

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Fats and oils

Fats are a necessary part of our diet. In nature, they can be found in every higher form of life, in every organic compound. They are energetically the richest of all biomaterials found in nature. For that reason, every organism builds up a supply of fats in its cells.

Fats and oils are esters of various carboxylic acids with glycerine. Glycerine has in its molecule three

hydroxyl groups. These can interact with both saturated and unsaturated carboxylic acids to form various lengths of molecules held together by ester bonds. Carboxylic acids bond using this esteric bond to the hydroxylic group of glycerine. This bond can be broken using a base. In the dissociation reaction that follows, the salt of an alkaline metal is formed, as is carboxylic acid and glycerine. Because glycerine can bond with three carboxylic acids, we call both fats and oils triglycerides.

Fats contain saturated carboxylic acids and are therefore solid. The length of their chain ranges between 16 and 18 carbon atoms. Animal fat mostly contains palmitic, stearic and oleic acids. Plant fats, on the other hand, contain unsaturated acids which animal cells are unable to synthesise.

Since these are essential to good health, animals must consume them in order to maintain normal life functions. A large number of unsaturated fatty acids reduces melting point. Fats are not soluble in water, but they are very soluble in organic solvents. Of all the various biomaterials, fats contain the most joules. The number of joules a material contains is equivalent to the amount of energy one unit of material can release. The joule is a fairly new quantity. In the past, calories were used to measure the amount of energy, but now, the new unit of measurement is the joule, thanks to international agreement. Both units, however, can be seen as the measure of energy a food or other substance contains on its packaging in supermarkets and grocery stores.

Fats are present in every plant and animal cell because they are an ideal source of energy, and a good reserve material as well. Fat content in plant seeds can range up to 50% (cocoa, nuts, rape). In the cells of animals, fat is often stored in the form of fat tissue.

Vitamins are another significant basic material for our bodies. There are two types of vitamins: those that dissolve in water, and those that dissolve in fat. This is another reason why fats are so significant for our bodies. They serve as a transportation system for some of the vitamins we ingest. An organism which is completely lacking in fat could also lack some of the vitamins necessary to our health, and could fall ill, on the one hand because of a lack of fats, on the other hand because vitamins ingested could not be dissolved, and could therefore not be used. For example, the vitamins contained in carrots could not be ingested if not for the presence of fats.

Oils are esters of glycerine with mostly unsaturated carboxylic acids. Under normal conditions they are found as liquids.

Because fats and oils are actually mixtures of esters, they do not have one clear boiling point. We speak rather of an area of boiling, an approximate temperature. This temperature is lower the more unsaturated bonds of carboxylic acids contained in the triglyceride. Fats and oils are lighter than water in their pure form. They are odourless and tasteless.

Fats and oils are used in the cosmetic industry, in the production of cleaning products and of course in the production of food products.

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Sugars

Sugars is the general term given to the widest variety of naturally-occurring substances.

In the past, hydrocarbons were incorrectly understood as the hydrates of carbon, hence the name hydrocarbons. The new name of this group is saccharides. Sugars are, however, chemically polyalcohols whose primary and secondary hydroxyl groups have oxidised to an aldehyde or ketone group.

Sugars are compounds whose chemical properties are similar to those of sugars. We can differentiate between monosaccharides, oligosaccharides and polysaccharides (sacharum = Latin sugar). Monosaccharides are simple sugars and represent the basic building block of oligosaccharides and polysaccharides. Monosaccharides can be synthetically produced by the oxidation of chain alcohols which have multiple hydroxyl groups. The product of this reaction is one aldehyde group.

According to the number of carbon atoms in a molecule, we can differentiate between biosams (2), triosams (3), tetrosams (4), pentosams (5), hexosams (6) and heptosams (7). Monosaccharides usually have a circular shape. The ring is composed of one atom of oxygen with 4 or 5 carbon atoms.

Biologically important hexosams include glucose and fructose. In glucose, the ring closes between carbon atoms C1 and C5. In fructose, the ring closes between atoms C2 and C6.

One of the most important monosaccharides is glucose, with the chemical formula C6H12O6. Most living organisms are able to break down glucose the fastest, using the energy its bonds contained.

Glucose is produced in plants from carbon dioxide and water thanks to the photochemical process known as photosynthesis. Plants then store glucose, usually changing it into starch, which is used as a reserve substance. Animals, on the other hand, use glycogen as an energy reserve. Glycogen is a polysaccharide, as is glucose.

Oligosaccharides are composed of two to ten molecules of monosaccharides which are bonded together by a glycosidic bond. Sucrose (beet sugar, raw sugar) is a disaccharide composed of one molecule of glucose and one molecule of fructose. The mutual bond lies between hydroxyl groups on atom C1 of glucose and the hydroxyl group of atom C2 of fructose. In the synthesis reaction which bonds these two groups, a water molecule is produced. This type of reaction is known as a condensation reaction. Another disaccharide is maltose. Maltose is produced during the digestion of starch and in the kernels of cereal grains. It is composed of two molecules of glucose.

Polysaccharides are composed of more than ten monosaccharides. They are biological macromolecules. The most significant polysaccharides found in nature are starch and cellulose. Starches are granary sugars in plants. They are composed of a molecule of glucose which is bonded with a glycosidic bond a -1,4- and occurs as amylose or amylopectin. Amylose is a molecule composed of around 10,000 molecules of glucose. Amylopectin is made of around 1 million glucose ligands. Contrary to amylose, it is branched. Cellulose is composed of glucose molecules, but of course, these are bonded together with glycosidic bonds b - 1,4. Cellulose is formed by an unbranched chain which is arranged in the cellular walls of plants, with 60-70 molecules grouped together, so-called microfibriles. Hydrogen bonds form between molecules of cellulose. Animals are not capable of breaking down the glycosidic bonds of cellulose b -1,4-. For this reason, cellulose is not a desirable foodstuff for animals, although its building blocks are molecules of glucose. Ruminants (livestock) can digest cellulose, because their stomachs include bacteria which can breakdown cellulose. This bacteria living in the stomachs of ruminants is an example of symbiosis.

Verification

The verification of glucose is carried out using a technique called the Fehling tests (a Fehling solution with mmj. Is made of copper sulphates and tartrate – salts of wine acids). After warming, the Fehling solution, which was blue, produces a reddish, cubic copper oxide precipitate.

Štarches are indicated with the help of a solution of mixed iodine in potassium iodide (a Lugol solution). In the presence of starch, the solution turns blue. This colouring comes about by the addition of iodine to the spirally-shaped starch. When heated, the spiralled structure straightens out, at which time molecules of iodine are released, and the blue colour disappears. When the solution is cooled, the blue colour reappears, because the helical structure is renewed, and iodine adds onto the compound.

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Proteins, the building blocks of life

Amino acids are among the organic compounds with multiple functional groups. They are important compounds found in living organisms, forming most importantly proteins. There are 20 amino acids which occur most frequently in nature. All amino acids have one carboxylic group (-COOH-) and one amino group (-NH2). Naturally-occurring amino acids have an amino group bonded to a carbon atom a - and are therefore called a -amino acids. The rest of the molecule ( R ) can have a variety of structures.This molecule rest is called a lateral chain. Synthetic amino acids can contain an amino group and other carbon atoms.

The naming of amino acids is derived from the names included in other hydrocarbon chain compounds. The simplest amino acid is glycine, which is derived from ethane and is therefore called acid a -aminoethane. With more complex amino acids, however, systematic names are used only rarely. It is more usual to use their trivial names, with the various prefixes of three letters added onto the beginning of glycin: gly, alanin, ala, leucin, leu, and so forth.

Amino acids can be categorised according to the chemical properties of their lateral chains. There are neutral amino acids, basic amino acids and acidic amino acids. Neutral amino acids have a hydrocarbon lateral chain which can be of either polar or non-polar character. Basic amino acids contain an extra amino group in their lateral chains. Acidic amino acids contain a carboxylic group in their lateral chains.

A condensation is a chemical reaction in which molecules in larger aggregates join together, and release water in so doing. Among the amino acids, condensation can come about when the bond between an amino group of an amino acid and the carboxylic group of a second amino acid join together.

This bond, the result of a condensation reaction of two amino acids, is called a peptide bond It is given by the chemical formula (-CO-NH-).

The bonding of a large number of amino acids can result in a long-chained amino acid. The synthesis of this type of chained molecule is called a polycondensation.

Thanks to its functional group, amino acids show some of the same characteristics as bases, as well as some of those characteristics shown by acids. Compounds which react as both bases and acids are called ampholytes. In an aqueous solution or in the solid phase of matter, the carboxylic group is negatively charged. If protons are released into solution, and an amino group accepts one of the protons, it becomes positively charged. Because amino acids are charged both positively and negatively at the same time, we call them amphions. In an acidic environment (low pH value due to the presence of excess positively charged protons), an amino group is able to accept one of these protons, so that a positively charged ion is produced. As long as the concentration of free protons drops below a certain value (pH increases), the carboxylic group loses its proton, becoming a negatively charged ion - an anion.

Appearance and significance

Peptides and proteins are molecules made of amino acids. They occur in living organisms and in every known group of natural substances, and they serve a number of purposes.

Peptides are chains which are composed of up to 100 amino acids, all bonded together by peptide bonds. Formation of the chain is possible thanks to the presence of both functional groups in the amino acid molecule. The beginning of the peptide chain always starts with an amino acid bond which has a free amino group (with N at the end). At the other end of the peptide chain is an amino group with a free carboxylic group (with C at the end). Peptides can be divided into oligopeptides (2-9 amino acids) and polypeptides (10-100 amino acids). Peptides are, for example, important as hormones which run our bodily functions.

Albumens and proteins

Albumens and proteins are macromolecules which are composed of more than 100 naturally-occurring amino acids. Amino acids bond one to the next, as in peptides bonded together with a peptide bond. A chain of proteins is composed of a certain number and order of 20 amino acids, which we call an amino acid sequence. When we combine the 20 most often occurring amino acids in all their myriad ways as macromolecules, we get an unbelievable amount of combinations, or of different proteins. Because proteins can form very long molecules, we call them macromolecules (makros = Greek big). Every protein has its typical amino acid sequence. These are called primary structure proteins. Protein molecules have a certain spatial structure as well. Their molecules can be spiral in shape, or they can have the shape of a folded leaf. These types of protein structures are called secondary structure proteins. This structure is typical for the fibrous proteins of animals. In globular proteins, the spiral structure and the folded structure are merged thanks to both structures serving mutually necessary functions. The result is the formation of a spherically shaped structure. This globular structure is a three-dimensional protein structure and is held in place with the help of van der Waals forces, which keep its ions attracted to sulphide bridges. Although fibrous proteins are not water soluble, globular proteins do mix with water.

Proteins are one of the most important constituents of the structure of living organisms. They form enzymes, antibodies and some hormones.

Proteins turn yellow in the presence of nitric acid (xanthoprotein reaction). If, however, nitric acid comes into contact with the skin, for example on the hand, a yellow-brown spot appears that will not wash off and will fade only very slowly. Proteins denature when heated or when in the presence of alcohol, because their three-dimensional structure is destroyed. The protein loses its solubility, and falls out of, or precipitates out of, solution.

Hydrolysis as the opposite of condensation

Protein and peptide chains can be dissociated, or broken down, into their basic building blocks, or into amino acids. In this reaction, the peptide bonds are broken, and water molecules are bonded onto their constituent parts. This is called a hydrolysis reaction, and it is the opposite of a condensation reaction. The hydrolysis of peptides and proteins takes place in the cells of living organisms, as well as when organisms digest foods in their digestive systems. Enzymes take part in this process as well, accelerating it in a way similar to that of a catalyst.

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