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CHEMICAL COMPOSITION OF A CELL AND ITS PHYSICAL AND CHEMICAL PROPERTIES

The elemental composition of the cell (protoplasm). To clearly imagine the biological and physicochemical properties of tissues, it is necessary to know the chemical composition of the protoplasm of the cell. In addition to water, there are a large number of elements in the protoplasm. The finest chemical studies have found that out of 104 elements of D. I. Mendeleev's periodic system, 96 are part of the protoplasm. Four elements — carbon, oxygen, hydrogen and nitrogen — make up about 96% of the body weight of a person or animal. The other four elements — calcium, phosphorus, potassium, and sulfur — account for only 3%, and all the rest — about 1%. The content of individual elements in the protoplasm is a fraction of a percent, and some of them are found in some cells, others in others. So, for the cells of the thyroid gland, the presence of iodine, which is not available in the cells of other organs, is characteristic. Thus, already in the elemental composition of living features of community and differences of individual cells are found.

A special group consists of the so-called trace elements. Their common features are, firstly, that they have an effect in extremely insignificant doses (within 10 ~ 8-10 ~ 12%); secondly, each of them acts specifically and cannot be replaced by another element. There is reason to believe that trace elements are catalysts that play an important role in the conversion of substances in the cell. It has been established that a number of trace elements are involved in intracellular metabolism, affecting growth and development, participating in the synthesis of hormones and vitamins. So, copper together with proteins forms enzymes, and iodine, barium, cobalt, manganese, zinc, aluminum accelerate the work of some enzymes. Individual trace elements alter the physical state of colloidal solutions. For example, aluminum increases viscosity and lowers permeability.

Substances that make up the cell. A variety of chemical elements are in the cells in the form of organic and inorganic compounds.

Organic matter is that substrate without which a special form of matter motion called life is impossible. The reasons for this lie in the structural features of organic substances related to polymers. The polymer molecules are gigantic and consist of hundreds and thousands of simpler compounds called monomers. The latter, connecting with each other, form long chains. This structure allows polymers to combine the properties of stability and variability. Huge polymer molecules are not subject to Brownian motion, and therefore spatial organization of complex chemical reactions is possible based on them. Changing the sequence of monomers and the spatial distribution of polymer chains affects the properties of the substance.

The most important organic substances are: proteins, fats, carbohydrates, nucleic acids and adenosine triphosphoric acid (ATP).

Squirrels. The elemental composition of proteins is represented by carbon (about 50%), oxygen (approximately 25%), nitrogen (on average 16%), hydrogen (up to 8%) and sulfur (0.3–2.5%). In some proteins, phosphorus, iron, magnesium, manganese, and other macro- and microelements are present in small quantities. Proteins make up 50–70% of the dry matter of the animal’s body. It is with proteins that the basic manifestations of cell life are inextricably linked; protein features to a greater extent determine the properties of individual

cells, tissues, organs and whole organisms. Regarding protein, F. Engels also wrote: “Everywhere we meet life, we find that it is associated with some kind of protein body, and everywhere we meet some kind of protein body that is not in the process of decomposition, we are we encounter exceptions and phenomena of life ”*.

The biological role of proteins consists primarily in the fact that they underlie the structure of various components of cells and tissues, and specialized structures, thanks to proteins, carry out their basic functions. So, muscle proteins are responsible for the ability of these tissues to contract, erythrocyte proteins - for their ability to transport oxygen, etc. Having both stability and variability as polymers, proteins are responsible (along with nucleic acids) for the constancy of various structures and processes, occurring in the cell, and for their ability to change limitedly. The latter enables living things to adapt to changing living conditions.

Proteins are composed of amino acid residues joined by peptide bonds. In total, approximately 20 different amino acids enter proteins. The sequence of alternation of these twenty monomers gives an extremely large number of combinations of various protein molecules and thereby determines the specificity and biological activity of proteins. Amino acids are derivatives of carboxylic acids in which one or more hydrogen atoms are replaced by an amino group (—NH2). The amino acids that make up proteins are a-amino acids in structure, that is, the amine group is attached to the carbon atom closest to the carboxyl. In cases where the amino acid contains two amino groups, the second is attached to the extreme carbon atom. Since both acidic (carboxyl — COOH) and basic (amino — NH2) groups are simultaneously present in amino acids, they belong to amphoteric compounds, that is, they are capable of reacting either as acids with alkalis or as alkalis with acids depending on the state of the medium in which the reaction occurs.

The most important property of amino acids, which determines the possibility of protein formation, is the ability to combine by forming a bond between the carboxyl and amine groups of two amino acids with the release of water. This method of combining amino acids is called a peptide bond:

-H20

CH3 — CH (NH2) —COOH + HHN — CH2 — COOH— *

alginine | | glycine

- ^ CH3 — CH (NHg) - jCa ^ NHJ —CH2 — COOH

alanyl glycine

The combination of two amino acids is called a dipeptide, three is called a tripeptide, and a peptide consisting of a small amount of amino acids is called an oligo peptide.

If the number of amino acids in a molecule is large, then the substance is called a polypeptide.

Proteins are distinguished between simple and complex. Simple ones include those that consist only of amino acids (amino acid residues): albumin, globulins (milk, egg, whey), fibrinogen, myosin, etc. Complex proteins, or proteides, consist of proteins and non-protein part (simple

tic group). All proteids are divided into groups depending on the nature of the non-protein part.

L Glycoproteins are complex compounds where the protein is tightly bound to carbohydrates. These include mucin, which includes an amino-containing carbohydrate - glucosamine, and mucoids containing amino sugar

- chondrazamine.

2. Phosphoproteins - the protein is bound to phosphoric acid by an ether bond. Phosphoproteins are milk casein and chicken vitellin.

3. Lipoproteins - proteins associated with fat-like substances, lipoids. Membranes of almost all cellular structures and organelles are formed from lipoproteins: nucleus, mitochondria, lamellar complex, cytoplasmic reticulum, lysosome and membrane of secretory granules.

4. Chromoproteins are compounds consisting of a protein bound to a non-protein pigment. These include hemoglobin (protein - globin and pigment - heme), with the help of which oxygen and carbon dioxide are transferred by blood, myoglobin - respiratory pigment of muscle cells and the combination of chlorophyll with protein - with its help plants absorb carbon dioxide.

5. Nucleoproteins - a compound of proteins with nucleic acids. Their acidic character is determined by the presence of phosphoric acid, which is very important in many processes in a living organism.

6. Metalloproteins - compounds of proteins and metals. These are mainly proteins with enzymatic properties: catalase, peroxidase, cytochromes containing iron, etc.

The chemical, physico-chemical and biological properties of proteins are determined not only by the composition of amino acids and the sequence of their compounds in the protein molecule, but also by the configuration of the polypeptide chains in the whole molecule as a whole. Particles of some proteins have a rounded (ellipsoidal) shape — globular proteins (albumin, globulin, hemoglobin, pepsin, etc.). Particles of other proteins - fibrillar (myosin, keratin, collagen, ellastin, etc.) are represented by the finest threads and fibers.

In recent years, the internal structure of protein molecules has been established by x-ray diffraction analysis. Proteins have been shown to have primary, secondary, tertiary and quaternary structures. The primary structure is understood to mean the sequence of arrangement of amino acid residues in the polypeptide chain of a protein molecule. Spiralization, that is, twisting into a spiral of a polypeptide chain of a protein molecule with the formation of hydrogen bonds between CO - and hydrogen peptide bonds, represents the secondary structure of the protein. The tertiary structure of the molecule is its spatial arrangement (packaging), which, together with the secondary structure, gives the active center of the protein molecule a certain position of the functional groups, which provides affinity for one or another substrate. The quaternary structure of a protein is a combination of several polypeptide chains connected by weak (non-covalent) bonds, representing a single molecular formation in structural and functional terms.

The molecular weight of proteins is extremely large and, depending on the type of protein, ranges from tens of thousands, reaching in some cases several million.

In the cells there are hydrophilic proteins that easily bind to water, giving colloidal solutions, and hydrophobic proteins that do not enter

in conjunction with water. Some proteins form crystals. Well crystallized, for example, hemoglobin of red blood cells.

Being united by the principle of chemical structure, the qualities of proteins found in nature and within the same organism are extremely diverse. This is primarily due to the different set and different combination within the protein molecule of individual amino acids, that is, the primary structure of the protein. The number of combinations of all these elements is huge. A variety of proteins also depends on its secondary and tertiary structures. As a result, not only animal and plant cell proteins are different, but also cell proteins of different tissues of the same organism. So, it is assumed that in humans there are over 100,000 types of proteins. However, the closer the organic forms are genetically closer to each other, the smaller the qualitative differences between their proteins.

Carbohydrates in the cell are found in the form of monosaccharides (simple carbohydrates) and polysaccharides (polymeric carbohydrates). The monomers of the latter are sugars. A typical monosaccharide is glucose, or grape sugar, which is in the form of a solution in the cell. Polysaccharides are widely distributed in animal and plant organisms in the form of fiber, starch, glycogen, mucopolysaccharides. Most polysaccharides, since they are poorly soluble in water, form clusters visible under the microscope in the cell.

In the body, carbohydrates, firstly, play the role of energy substances, since the energy released during their oxidation and glycolysis is used by the body to carry out a number of biological processes. Some carbohydrates are part of proteins, enzymes, nucleic acids and other biologically active substances. Acid mucopolysaccharides are part of the connective tissue (hyaluronic acid), cartilage (chondroitinseric acid), liver, muscles (heparin), etc. A number of carbohydrates are involved in the construction of cell membranes and organelles. The carbohydrate content in the cell can vary greatly depending on the type and physiological state of the cell. In general, their number in animal cells is lower than in plant cells.

The lipids that make up the cell are divided into two groups: neutral fats and lipoids (fat-like substances). Neutral fats are composed of glycerol and fatty acids. Lipoids, like fats, are soluble in organic solvents but have different chemical structures.

Lipids in the cell play both the role of reserve nutrients and the plastic material that builds the body of the cell. As spare substances, fats are of exceptional value due to the fact that they combine high calorie content with low density. In case of high energy costs, reserve fats are mobilized by the body and are eliminated from the cell without harm to the vital functions. Oxidizing, such fats emit a huge amount of energy, which is used to carry out a number of physiological processes. Spare fats often accumulate in the cell in significant quantities. After special staining, they are clearly visible under the microscope. The plastic material is mainly fat-like substances. They are part of organelles, membranes and other parts of the cell. Since these substances are constructive, their destruction leads to disruption of cell activity.

Fig.
1. The structure of a small section of a DNA molecule:

D - deoxyribose (carbohydrate); F - phosphate. Purine nitrogen bases: A - • adenine, G - guanine; pyrimidine: C - cytosine, T - thymine; / - phosphate-carbohydrate chain; 2 — hydrogen bond between nitrogenous bases; 3 - the border of one nucleotide of DNA; 4 - nitrogenous bases connected by a hydrogen bond; 5 - imaginary axis of the DNA molecule.





Two types of nucleic acids are known: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both acids are macromolecular compounds, the molecule of which is formed from a huge number of monomers called nucleotides. They are able to form chains longer than the amino acids in the protein. As a result, the molecular weight of nucleic acids is higher than that of proteins, and their molecules can be seen with an electron microscope.

The composition of nucleotides includes: phosphoric acid, sugar, a nitrogenous base. The sugar base in DNA is represented by deoxyribose, and in RNA by ribose. The nitrogen bases in DNA and RNA are two purines - adenine and guanine and two pyrimidines - cytosine and thymine (DNA), cytosine and uracil (RNA). Thus, for RNA and DNA, the three types of nucleotides are the same, and the fourth is different. When a DNA molecule is formed (Fig. 1), the nucleotides bind to each other using phosphate. The result is a chain. DNA consists of two similar chains that are connected to each other via hydrogen bonds. In this case, four nucleotides are combined with each other as follows. A nucleotide with a purine nitrogenous base of one chain is necessarily connected to a nucleotide containing a pyrimidine base in another chain, with adenine connecting only with thymine, and guanine only with cytosine. Such connections are called complementary.

The double chain of the DNA molecule is twisted in the form of a long spiral and. In some periods of life, DNA cells are capable of self-reproduction; in other periods, it becomes the matrix on which the RNA molecule is built.

Self-reproduction begins with the breaking of hydrogen bonds (Fig. 1, 2) with the participation of enzymes, and the double DNA strand is divided into two single ones. Each of the single chains completes the second by joining on the basis of complementary bonds of free nucleotides from the environment. As a result, two completely identical molecules are formed from one. This process is called reduplication. The discovery of reduplication is one of the greatest achievements of molecular biology. In cell division, two completely similar DNA molecules are distributed between daughter cells. DNA molecule is relatively

Fig. 2. Scheme of DNA reproduction and RNA formation (synthesis):

1 - part of the original DNA molecule; 2 - two single values, DNA nucleotide after breaking of hydrogen bonds; 3 and 4 - two “daughter” DNA molecules formed due to completion of “a” and “b” single chains of the original DNA molecule; DNA nucleotides: with purine nitrogenous bases (indicated by flags); 5 — with adennum; 6 - with guanine; with pyrimidine nitrogenous bases (indicated by a pentagon); 7 - with timshum; 8 - with cytosine; 9 - the beginning of the formation of RNA. Free RNA nucleotides from karyoplasma are complementary to a single DNA strand (matrix); 10 - “hybrid” molecule, consisting of a single DNA strand (matrix) and the RNA chain formed on it (c) \ And - the RNA molecule is already separated from its matrix. RNA nucleotides: with purine nitrogenous bases (flags in the figure); 12 - with adenine; / 3rd guanine; with pyrimidine nitrogenous bases (pentagons in the figure); 14 - with uracil; 15 - with chntozin; a, b — complementary nucleotide chains of the original DNA molecule; a ', b' - DNA nucleotide chains newly completed on the basis of complementary bonds; in -•

RNA nucleotide chain.

stable, its molecular weight is 6-8-10 million. In the period between cell divisions, DNA molecules produce RNA molecules.

RNA consists of one nucleotide chain and each is negatively charged. Due to the repulsion of identical charges, the RNA chain is in an extended state, forming irregular folds. If the charges are removed by any agents, then the RNA chain coagulates.

RNA formation begins with the separation of a double strand of DNA into single ones. The nucleotides of a single DNA strand are joined by nucleotides complementary to them from the environment; only adenine instead of thymine (as in the formation of DNA) joins uracil. Между присоединенными нуклеотидами устанавливается связь, после чего вся цепочка новообразованной РНК отходит от ДНК, а последняя «штампует» новую молекулу РНК (рис. 2). РНК передает информацию о последовательности нуклеотидов в ДНК и непосредственно участвует в синтезе бел ков. В клетке находится несколько разновидностей РНК: транспортная — наиболее низкополимерная; информационная — более высокополимерная и рибосомаль-ная — самая высокополимерная РНК (с молекулярной массой 1,5—2 млн.). Все они участвуют, хотя и по-разному, в синтезе белков.

Аденозинтрифосфорная кислота (АТФ), так же как белки и нуклеиновые кислоты, — обязательная составная часть всех живых организмов. Биологическая роль этого соединения определяется присутствием двух фосфорсодержащих групп. Под воздействием фермента эти группы одна за другой легко отщепляются с освобождением большого количества свободной энергии, которая используется для осуществления различных физиологических функций клетки. Таким образом, АТФ является аккумулятором энергии.

Неорганические вещества главным образом представлены водой и различными минеральными вещеествами. Вода — необходимая составная часть клеток. Она находится в свободном и связанном состоянии. Свободная вода (95%) — растворитель. В форме водных растворов в клетку поступает ряд веществ из внешней среды, и с водой из клетки выводятся продукты обмена. Свободная вода образует также среду, в которой протекают многие реакции, а благодаря своей теплоемкости предохраняет клетку от резких колебаний температуры. Связанная вода вместе с другими веществами участвует в образовании ряда морфологических компонентов клетки. Она входит в состав сольватных оболочек и удерживается молекулами белка при помощи водородных связей. Значение воды в жизни клеток ярко демонстрируется тем фактом, что смерть при ее отсутствии наступает раньше, чем при отсутствии пищи. Количество воды в клетке колеблется от 60 до 80%. Это зависит от вида клетки, ее состояния и возраста. Так, в эмбриональных тканях воды значительно больше, чем в клетках взрослого организма.

Минеральные вещества вместе с органическими участвуют в обмене веществ. Среди минеральных веществ особенно большое значение имеют соли. Наиболее распространены в животных тканях соли угольной, соляной, серной и фосфорной кислот. Минеральные соли, растворимые в жидкостях, обусловливают осмотическое давление, от которого зависит проникновение веществ из клетки и внутрь нее, перемещение веществ внутри клетки и другие явления. Соли влияют на коллоидное состояние высокомолекулярных веществ клетки, что отражается на ее физических свойствах. Растворимые минеральные вещества поддерживают кислотно-щелочное равновесие, определяя таким образом реакцию среды, которой в значительной мере определяется течение сложных превращений веществ, связанных с осуществлением жизненных процессов в клетке. Например, белки, обладающие амфо-терными свойствами, в кислой среде ведут себя, как щелочи, а в щелочной — как кислоты. Некоторые минеральные вещества приобретают большое значение в соединениях с органическими веществами. В отдельных тканях минеральные вещества играют механическую роль, придавая им прочность и крепость.

Все названные выше элементы и вещества образуют в клетке сложную единую систему, в которой изменение одних компонентов влечет за собой изменение других частей этой системы.

Физическое состояние веществ, составляющих клетку. Клетка является неоднородной системой. Разные ее компоненты имеют различное агрегатное состояние и обладают поэтому различными показателями вязкости, эластичности, электропроводности, преломления и пр. Многие из этих свойств непостоянны и меняются с изменением состояния химических веществ. Некоторые вещества находятся в клетке в виде истинных растворов, когда растворенное вещество находится в состоянии молекул или ионов. Большинство веществ в клетке образует коллоидные растворы, то есть растворы, в которых частицы рассеянного вещества достигают относительно больших размеров — от 1 до 100—500 нм (миллимикрон). Чем меньше частица, тем выше сила адсорбции — способность частиц удерживать другие вещества. Адсорбция играет важную роль в жизни клетки. С адсорбции в клетке начинается большинство реакций, связанных с дыханием, питанием и другими процессами. Это же явление обусловливает согласованное действие различных ферментов, в результате чего усиливается или замедляется обмен веществ и пр.

Коллоидные растворы представляют всегда двухфазную систему: одна фаза — растворитель (дисперсионная среда), а другая — рассеянные в растворителе коллоидные частицы (дисперсная фаза). Диспергированные частицы

Fig. 3. Схема строения геля:

1 — мицелла; 2 — часть ее, лишенная соль-ватной оболочки; 3—сольватная оболочка; 4 — дисперсионная среда.

Fig. 4. Схема коацервации:

1 — коллоидная частичка; 2 — плотный

слой и 3 — разреженный слой сольватной

оболочки; 4 — дисперсионная среда.

мицеллы имеют разнообразную форму (шарообразную, овальную, удлиненную). Благодаря одноименному электрическому заряду и сродству к растворителю мицеллы находятся во взвешенном состоянии. Коллоиды, устойчивость которых обусловлена только зарядом, называются гидрофобными.

В отличие от них гидрофильные коллоиды более устойчивы, так как их мицеллы способны притягивать к себе молекулы воды, образующие вокруг них водный чехол (сольватная оболочка). Он вместе с зарядом препятствует слипанию мицелл. В том случае, когда дисперсная фаза распадается на отдельные мицеллы, коллоидный раствор приобретает более или менее вязкую консистенцию. Тогда говорят, что коллоидный раствор находится в состоянии золя (solvo— растворять).

При снятии заряда с частичной потерей водной оболочки мицеллы гидрофильных коллоидов сливаются, но лишь теми участками, где нет водной оболочки. В результате дисперсная фаза образует подобие решетки, в петлях которой находится растворитель. Таким образом, в данном случае дисперсная фаза и дисперсионная среда не отделяются одна от другой. Этот процесс называется желатинизацией, а сам раствор — гелем или желем (рис. 3). В результате желатинизации вся клетка в целом или отдельные ее части приобретают консистенцию плотного студня и становятся упругими и эластичными, подобно застывшему желатину. Процесс желатинизации обратим. При простом встряхивании или других воздействиях мицеллы, образующие дисперсную фазу геля, снова приобретают заряд, связь их нарушается и раствор разжижается, то есть гель снова переходит в золь. Этот процесс называется тиксотропией. Переход золя в жель (гель) и обратно происходит, например, при амебовидном движении клеток. Под влиянием электролитов, высоких температур и других внешних воздействий коллоиды могут терять заряд, но тогда частицы слипаются одна с другой и выпадают в осадок, то есть происходит разделение дисперсной фазы от дисперсионной среды. Этот процесс называется коагуляцией (coagulatio — свертывание). В результате коагуляции нередко в клетке образуются видимые под микроскопом структуры: зернистость, нитчатостьидр. Процессы коагуляции наблюдаются при неблагоприятных воздействиях и могут быть обратимы, но при смертельных изменениях клетки этот процесс становится необратимым.

В коллоидных растворах может происходить также коацервация. При этом мицеллы утрачивают наружный слой сольватной оболочки и сливаются при помощи ее внутренних слоев. В результате образуются крупные агрегаты — коацерваты, которые, однако, не сливаются друг с другом, как при коагуляции (рис. 4). Коацерваты в отличие от коагулята и геля имеют жидкую консистенцию. В клетке они имеют вид гранул. Часто гранулы коацерватов образуются под влиянием внешних агентов (некоторые красители), проникших в клетку. Это является защитной реакцией нормальной клеткич При ее повреждении коацервации и гранулообразования в ответ на введение инородных веществ не происходит. Коацервация, согласно гипотезе А. И. Опарина, сыграла важную роль в процессе возникновения жизни. В зависимости от физиологического состояния клетки (подвижности, интенсивности процессов питания и выделения, степени раздражимости), а также под влиянием воздействий внешней среды в коллоидных системах клетки процессы коагуляции, желатинизации и тиксотропии непрерывно сменяют друг друга. В живой клетке благодаря особой, исторически сложившейся организации живого вещества эти процессы могут быть пространственно разобщены и совершаться одновременно. Таким образом, цитоплазма клетки и отдельные ее частицы в одни периоды жизни являются жидкими, в другие — плотными.
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ХИМИЧЕСКИЙ СОСТАВ КЛЕТКИ И ЕЕ ФИЗИКО-ХИМИЧЕСКИЕ СВОЙСТВА

  1. PHYSICAL AND CHEMICAL PROPERTIES OF MILK
    Density - the mass of milk at 20 ° C, enclosed in a unit volume (kg / m3). In cows, it ranges from 1027— SHZkoz ^ 1027 ^ 1038, sheep ~ ^ ~ 1034-1038, mares - 1033-1035, buffalo - 1028-J.030. This property of milk is determined by the densities of its components (kg / m3): milk fat - 920, lactose - 1610, protein - 1390, salts - 2860, dry milk residue - 1370, dry fat-free residue -
  2. INFLUENCE OF DIFFERENT FACTORS ON DAIRY PRODUCTIVITY, CHEMICAL COMPOSITION AND PROPERTIES OF MILK
    Milk productivity, organoleptic, physico-chemical and technological properties of milk depend on the period of lactation, breed, age, quality of feeding, conditions, health status, milking, exercise, season, individual characteristics of lactating animals. Lactation periods. Lactation, in terms of changing the composition and properties of milk, can be divided into 3
  3. The chemical composition of water. Water pollution: physical, chemical, bacteriological. Self-cleaning ability of water sources
    The chemical composition of water. In nature, water almost always contains more or less mineral salts dissolved in it. The degree and mineral composition of water is determined by the nature of the soil or soils adjacent to aquifers or surface water sources. The amount of mineral salts contained in the water is expressed in mg / L. Organic matter Of these, the most important
  4. Физико%химические особенности
    Studying the anatomy of virions has provided a lot of useful information about the chemistry and molecular biological properties of elementary viral components. Sometimes this information made it possible to understand the purpose, the biological (physiological) meaning of the formation of various viral structures. Химическая структура вирусов по элементарному составу не позволяет выделить какие либо
  5. Physicochemical and physiological regulation of CBS
    In the body, the constancy of pH is supported in two ways: physicochemical (due to the adequate functioning of the buffer systems) and physiological. In addition to buffer systems, the physicochemical aspects of the regulation of CBS include the close interaction between the acid-base and electrolyte balance. The most important function in the physiological regulation of CBS is performed by the respiratory and urinary
  6. PHYSICAL AND CHEMICAL INDICATORS
    The species of animal meat can be determined by the melting temperature and the coefficient of refraction (refraction) of fat. These fat constants depend on the ratio in fat of saturated (saturated) and unsaturated (unsaturated) fatty acids. In addition, they put a reaction on glycogen, a precipitation reaction and determine the iodine number. Determination of the melting point of fat. Capillary diameter
  7. Experimental physiological, physicochemical direction
    In Russia, the founder of pathological physiology as an independent science and subject of teaching was an experimental physiologist, student I.M. Sechenova V.V. Pashutin, who headed the Department of General Pathology of the Medical Faculty of Kazan University since 1874, and since 1878 the St. Petersburg Medical and Surgical Academy. V.V. Pashutin published in 1878 and 1881. "Lectures of General Pathology
  8. CHEMICAL COMPOSITION
    The chemical composition of meat is very complex and depends on the type of animal, age, gender, fatness, level of feeding and other factors. The chemical composition of animal meat changes significantly in severe pathological conditions. The chemical composition of meat includes: water, proteins, fats and lipoids, carbohydrates, extractive substances, minerals, vitamins, enzymes and hormones. Chemical composition
  9. Organoleptic and physico-chemical characteristics of beef stew of different producers
    Shikhaleva K.A., Evangelist I.A. Supervisor: Associate Professor, Department of General Chemistry and Environmental Monitoring Gumenyuk O.A. Federal State-Funded Educational Institution of Higher Professional Education “Ural State Academy of Veterinary Medicine”, Troitsk Out of more than 100 canned goods, meat processing enterprises produce mainly the least labor-intensive products, such as stewed beef. Braised beef is
  10. Soil chemistry
    It has now been established that the human body contains about 60 different chemical elements, which is about 0.6% of the total weight. The presence of trace elements, even in small amounts, is constantly associated with their role in the absorption of nitrogen and photosynthesis. Only to maintain the normal composition of human blood, about 25 microelements are needed, and their composition includes breast milk
  11. CHEMICAL COMPOSITION
    The chemical composition of honey is very complex and diverse (table. 29). It contains over 100 components necessary for the body. These substances can be represented as follows: As can be seen from the table, the main components of honey are fruit (fructose) and grape (glucose) sugar. As a rule, there is more fruit sugar (40%) than grape sugar (35%). Amount of fruit and grape
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