Download the presentation on the chemistry of enzymes. Enzymes. Properties and structure of enzymes. Ribozymes Despite the fact that most ribozymes are quite rare in cells, sometimes they are very important for their existence. on

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Enzymes or enzymes (from Latin fermentum, Greek ζύμη, ἔνζυμον - yeast, leaven) are usually protein molecules or RNA molecules or their complexes that accelerate (catalyze) chemical reactions in living systems. The reactants in a reaction catalyzed by enzymes are called substrates, and the resulting substances are called products. Enzymes are specific to substrates (ATPase catalyzes the cleavage of only ATP, and phosphorylase kinase phosphorylates only phosphorylase) Enzyme activity can be regulated by activators and inhibitors (activators - increase, inhibitors - decrease) Protein enzymes are synthesized on ribosomes, and RNA - in the nucleus. The terms “enzyme” and “enzyme” have long been used as synonyms (the first mainly in Russian and German scientific literature, the second in English and French). The science of enzymes is called enzymology, not fermentology (so as not to confuse the roots of the Latin and Greek words languages).

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Classification of enzymes

Based on the type of reactions they catalyze, enzymes are divided into 6 classes according to the hierarchical classification of enzymes (EC, Enzyme Commission code). The classification was proposed by the International Union of Biochemistry and Molecular Biology. Each class contains subclasses, so that the enzyme is described by a set of four numbers separated by dots. For example, pepsin has the EU name 3.4.23.1. The first number roughly describes the mechanism of the reaction catalyzed by the enzyme: EF 1: Oxidoreductases that catalyze oxidation or reduction. Example: catalase, alcohol dehydrogenase EC 2: Transferases that catalyze the transfer of chemical groups from one substrate molecule to another. Among transferases, kinases that transfer a phosphate group, usually from an ATP molecule, are especially distinguished. CF 3: Hydrolases that catalyze the hydrolysis of chemical bonds. Example: esterases, pepsin, trypsin, amylase, lipoprotein lipase EF 4: Lyases that catalyze the breaking of chemical bonds without hydrolysis with the formation of a double bond in one of the products. EC 5: Isomerases that catalyze structural or geometric changes in the substrate molecule. EC 6: Ligases that catalyze the formation of chemical bonds between substrates due to ATP hydrolysis. Example: DNA polymerase Being catalysts, enzymes accelerate both forward and reverse reactions, therefore, for example, lyases are able to catalyze the reverse reaction - addition at double bonds.

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Enzyme naming conventions

Enzymes are usually named by the type of reaction they catalyze, adding the suffix -ase to the name of the substrate (for example, lactase is an enzyme involved in the conversion of lactose). Thus, different enzymes performing the same function will have the same name. Such enzymes are distinguished by other properties, for example, by optimal pH (alkaline phosphatase) or localization in the cell (membrane ATPase).

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Functions of enzymes

Enzymes are proteins that are biological catalysts. Enzymes are present in all living cells and help convert some substances (substrates) into others (products). Enzymes act as catalysts in almost all biochemical reactions occurring in living organisms—they catalyze about 4,000 bioreactions. Enzymes play a vital role in all life processes, directing and regulating the body's metabolism. Like all catalysts, enzymes speed up both forward and reverse reactions, lowering the activation energy of the process. In this case, the chemical equilibrium does not shift either forward or backward. A distinctive feature of enzymes compared to non-protein catalysts is their high specificity - the binding constant of some substrates to protein can reach 10−10 mol/l or less. See also Catalytically perfect enzyme Enzymes are widely used in the national economy - food, textile industries, and in pharmacology.

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Kinetic studies

The simplest description of the kinetics of single-substrate enzymatic reactions is the Michaelis-Menten equation (see figure). To date, several mechanisms of enzyme action have been described. For example, the action of many enzymes is described by the ping-pong mechanism.

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Saturation curve of a chemical reaction illustrating the relationship between substrate concentration [S] and reaction rate v

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Specificity

Enzymes generally exhibit high specificity for their substrates. This is achieved by partial complementarity between the shape, charge distribution and hydrophobic regions on the substrate molecule and the substrate binding site on the enzyme. The enzymes exhibit high levels of stereospecificity, regioselectivity and chemoselectivity.

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Structure and mechanism of action of enzymes

The activity of enzymes is determined by their three-dimensional structure. Like all proteins, enzymes are synthesized as a linear chain of amino acids that folds in a specific way. Each sequence of amino acids folds in a special way, and the resulting molecule (protein globule) has unique properties. Several protein chains can be combined to form a protein complex. The tertiary structure of proteins is destroyed by heat or exposure to certain chemicals. To catalyze a reaction, an enzyme must bind to one or more substrates. The protein chain of the enzyme folds in such a way that a gap, or depression, is formed on the surface of the globule where substrates bind. This region is called the substrate binding site. It usually coincides with or is close to the active site of the enzyme. Some enzymes also contain binding sites for cofactors or metal ions. Some enzymes have small molecule binding sites and may be substrates or products of the metabolic pathway in which the enzyme enters. They decrease or increase the activity of the enzyme, which creates the opportunity for feedback. The active centers of some enzymes are characterized by the phenomenon of cooperativity.

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Induced correspondence model

In 1958, Daniel Koshland proposed a modification of the key-lock model. Enzymes are generally not rigid, but flexible molecules. The active site of an enzyme can change conformation upon binding of a substrate. The amino acid side groups of the active site assume a position that allows the enzyme to perform its catalytic function. In some cases, the substrate molecule also changes conformation after binding at the active site. Unlike the key-lock model, the induced-fit model explains not only the specificity of enzymes, but also the stabilization of the transition state.

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Key-lock model

In 1890, Emil Fischer proposed that the specificity of enzymes is determined by the exact match between the shape of the enzyme and the substrate. This assumption is called the key-lock model. The enzyme combines with the substrate to form a short-lived enzyme-substrate complex. However, although this model explains the high specificity of enzymes, it does not explain the phenomenon of transition state stabilization that is observed in practice.

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Modifications

Many enzymes undergo modifications after the synthesis of the protein chain, without which the enzyme does not fully exhibit its activity. Such modifications are called post-translational modifications (processing). One of the most common types of modification is the addition of chemical groups to side residues of the polypeptide chain. For example, the addition of a phosphoric acid residue is called phosphorylation and is catalyzed by the enzyme kinase. Many eukaryotic enzymes are glycosylated, that is, modified by oligomers of carbohydrate nature. Another common type of post-translational modification is cleavage of the polypeptide chain. For example, chymotrypsin (a protease involved in digestion) is obtained by cleaving a polypeptide region from chymotrypsinogen. Chymotrypsinogen is an inactive precursor of chymotrypsin and is synthesized in the pancreas. The inactive form is transported to the stomach, where it is converted into chymotrypsin. This mechanism is necessary in order to avoid the splitting of the pancreas and other tissues before the enzyme enters the stomach. The inactive enzyme precursor is also called a "zymogen".

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Koshland's induced correspondence conjecture

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A more realistic situation is in the case of induced correspondence. Wrong substrates - too big or too small - do not fit the active site

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Enzyme cofactors

Some enzymes perform the catalytic function on their own, without any additional components. However, there are enzymes that require non-protein components to carry out catalysis. Cofactors can be either inorganic molecules (metal ions, iron-sulfur clusters, etc.) or organic (for example, flavin or heme). Organic cofactors tightly bound to the enzyme are also called prosthetic groups. Organic cofactors that can be separated from the enzyme are called coenzymes. An enzyme that requires the presence of a cofactor for catalytic activity, but is not bound to it, is called an apo enzyme. An apo enzyme in combination with a cofactor is called a holo enzyme. Most cofactors are bound to the enzyme by noncovalent but rather strong interactions. There are also prosthetic groups that are covalently bound to the enzyme, for example, thiamine pyrophosphate in pyruvate dehydrogenase.

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Literature

Volkenshtein M.V., Dogonadze R.R., Madumarov A.K., Urushadze Z.D., Kharkats Yu.I. Theory of enzyme catalysis / Molecular Biology. 1972. 431-439. Koshland D. The Enzymes, V. I, Ch. 7. New York, Acad. Press, 1959. Dixon, M. Enzymes / M. Dixon, E. Webb. - In 3 volumes. - Trans. from English - T.1-2. - M.: Mir, 1982. - 808 p.

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Enzymes Enzymes are biological catalysts of a protein nature that accelerate chemical reactions in living organisms and outside them. J. Sumner was the first to obtain the enzyme urease in its pure form and proved that the action of enzymes is not associated with the cell. In addition to him, both domestic (K.S. Kirchhoff, I.P. Pavlov, S.E. Severin, V.A. Engelgard, etc.) and foreign scientists made significant contributions to enzymology, or enzymology, the study of enzymes (E. Fisher, J. Nortron, A. Spalanzini, M. Duclos, etc.).

Structure of enzymes single-component, two-component enzymes (simple proteins) (protein + active group) active group coenzyme prosthetic group (determines catalytic activity, protein part)

ENZYMES (according to the type of reaction catalyzed) Oxidoreductases are redox enzymes. Transferases are transfer enzymes. They transport individual groups, radicals and atoms, both between individual molecules and within them. Hydrolases are enzymes that accelerate hydrolysis reactions, i.e. the process of breaking down complex substances into simpler ones with the addition of water molecules. Lyases are enzymes that hydrolytically cleave various groups from substrates. Isomerases are enzymes that accelerate the isomerization of organic compounds (intramolecular rearrangements). Ligases are enzymes that accelerate the synthesis of complex compounds from simpler ones due to the breakdown of pyrophosphate bonds (ATP).

Properties of enzymes Selectivity (selectivity of their action) Determined by the ability of an enzyme to convert only a given type of substrate in certain reactions and conditions.

High catalytic activity The addition of a small concentration of enzyme accelerates the conversion of the substrate by 10 8 - 10 12 times. Stability Ability to maintain catalytic activity Specificity

Temperature Dependence Many enzymes are most effective at human body temperature, i.e. approximately at A person dies at lower and higher temperatures not so much because the disease killed him, but so much because the enzymes stop functioning, and therefore the metabolic processes that determine the existence of the organism stop. Dependence on pH of the environment Enzymes act most effectively on the substrate under a strictly defined solution environment.

pH values ​​of physiological fluids Medium pH value Possible deviations Gastric juice 1.7 0.9-2.0 Hepatic bile 7.4 6.2-8.5 Cystic bile 6.8 5.6-8.0 Blood (plasma) 7 .4 7.25-7.44 Urine 5.8 5.0-6.5 Sweat 7.4 4.2-7.8 Tear fluid 7.7 7.6-7.8 Saliva 6.8 5.6 -7.9 Cerebrospinal fluid 7.6 7.4-7.8 Upper colon juice 6.1 - Pancreatic juice 8.8 8.6-9 Small intestine juice 6.5 5.1-7.1

Some examples of the use of enzymes in industry enzyme industry use of Amylase (break down starch) Brewing Saccharification of starch contained in malt Textile Removal of starch applied to threads during sizing Bakery Starch - glucose. Yeast cells, fermenting glucose, produce carbon dioxide, the bubbles of which loosen the dough and give the bread a porous structure. The bread browns better and does not go stale longer.

Proteases (break down proteins) Papain Brewing Stages of the brewing process that regulate the quality of beer Meat Softening of meat. This enzyme is quite resistant to temperature increases and continues to act for some time when meat is heated. Then, of course, it is inactivated. Ficin Pharmaceutical Additive to toothpastes to remove plaque. Photo Washing gelatin from used film in order to extract the silver contained in it. Pepsin Food Production of ready-made cereals. Pharmaceutical Drugs that aid digestion (in addition to the normal action of pepsin in the stomach)

Trypsin Food Production of baby food products Renin Cheese making Milk coagulation (producing a casein coagulum) Bacterial proteinases Washing clothes Washing powders with enzymatic additives Tanning Hair separation - a method in which neither hair nor skin is damaged Textile Extracting wool from scraps of sheep skins Food Protein production hydrolysates (in particular for feed production)

Glucose oxidase Food Removal of glucose or oxygen Catalase Food Removal of hydrogen peroxide Rubber Production (from hydrogen peroxide) of oxygen necessary to convert latex into spongy rubber Cellulose Food Clarification of fruit juices Pectinase

Thousands and thousands of enzymatic reactions occur in the human body every second. - The enzyme amylase, which is found in saliva and in the juice of the small intestine, helps convert starch into maltose. - Maltose is then converted to glucose in the small intestine by the enzyme maltase. - In the stomach and small intestine, enzymes such as pepsin and trepsin convert proteins into simpler compounds called peptides. - Peptides are dissolved in the small intestine to amino acids under the action of enzymes - peptidases. - Lipase enzyme acts on fats (lipids) in the small intestine, breaking them down into glycerol and fatty acids.

Questions and tasks 1. What are enzymes? 2. How does the action of enzymes differ from the action of inorganic catalysts? 3.List the factors that affect the rate of an enzymatic reaction. 4. At what temperature do enzymes exhibit the greatest activity: 26, 36, 56 C? 5.Indicate the optimal pH values ​​for the action of amylase and pepsin. 6.How are enzymes classified and how are their trivial names formed? 7.Name the areas of application of enzymes in industry. 8. Citric acid is produced industrially by microbiological (enzymatic) fermentation of a sucrose solution according to the equation

How many kg of citric acid, with a yield of 62% of the theoretically possible, can be obtained from 520 kg of a 15% sucrose solution? 9. To produce lactic acid by microbiological (enzymatic) fermentation, industry uses starch and molasses. How many kilograms of lactic acid, with a yield of 75% of the theoretically possible, can be obtained from 640 kg of feed molasses, if the mass fraction of dry substances in it is 80%, of which sucrose accounts for 45%?

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Presentation by chemistry teacher of the State Budgetary Educational Institution “KMT” Zalieva N.M. Enzymes. Classification of enzymes. Features of the structure and properties of enzymes.

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ENZYMES (from Latin fermentum - fermentation, leaven) are enzymes, specific proteins that increase the rate of chemical reactions in the cells of all living organisms. The science of enzymes is called enzymology.

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The term "enzyme" was coined in the 17th century by the chemist van Helmont when discussing the mechanisms of digestion. History of the study

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In the 19th century Louis Pasteur, studying the transformation of carbohydrates into ethyl alcohol under the influence of yeast, came to the conclusion that this process (fermentation) is catalyzed by a certain vital force (enzyme) located in yeast cells, and he believed that these “forces” are inseparable from the structure of a living cell yeast. History of the study

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Eustace Liebig and his supporters, defending the chemical nature of fermentation, believed that it was a consequence of the formation of soluble enzymes in the cells of microorganisms. Louis Pasteur believed that fermentation is caused only by living microorganisms and that the fermentation process is inextricably linked with their vital activity. History of the study In the mid-19th century. A debate broke out about the nature of fermentation.

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History of the study The discussion between Liebig and Pasteur about the nature of fermentation was resolved in 1897 by Eduard Buchner, who, by grinding yeast with infusorial soil, isolated from them a cell-free soluble enzyme preparation (zimaza), which caused alcoholic fermentation. In 1907, Buchner was awarded the Nobel Prize in Chemistry “for his research work in biological chemistry and his discovery of extracellular fermentation.” Over the next 10 years, several more enzymes were isolated, and the protein nature of the enzymes was finally proven.

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The enzymes were first isolated in crystalline form in 1926 by James Betcheller Sumner and John Howard Northrop. In 1946 they were awarded the Nobel Prize. History of the Study James Betcheller Sumner John Howard Northrop.

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In 1961, a systematic nomenclature of enzymes was proposed by the Commission of the International Biochemical Union. Enzymes are divided into 6 groups according to the type of reaction they catalyze. The working name consisted of the name of the substrate, the type of catalytic reaction and the ending -ase. Example: lactan + dehydrogenation + aza = lactate dehydrogenase The previous names of pepsin and trypsin were retained for the known enzymes. Classification of enzymes

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Classification of enzymes Classes of enzymes Catalyzed reaction Examples of enzymes or their groups Oxidoreductases Transfer of hydrogen atoms or electrons from one substance to another. Dehydrogenase, oxidase Transferases Transfer of a certain group of atoms - methyl, acyl, phosphate or amino group - from one substance to another Transaminase, kinase Hydrolases Hydrolysis reactions Lipase, amylase, peptidase Lyases Non-hydrolytic addition to a substrate or detachment of a group of atoms from it. In this case, C-C, C-N, C-O or C-S bonds can be broken Decarboxylase, fumarase, aldolase Isomerases Intramolecular rearrangement Isomerase, mutase Ligases The connection of two molecules as a result of the formation of new bonds, associated with the breakdown of ATP Synthetase

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Typically, enzymes are isolated from animal tissues, plants, cells and cultural fluids of microorganisms, biological fluids (blood, lymph, etc.). Genetic engineering methods are used to obtain some difficult-to-obtain enzymes. Obtaining enzymes.

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Structure of enzymes Enzymes Simple - proteins Complex - proteins non-protein part or prosthetic group - coenzyme The protein part is called apoenzyme The protein part is called apoenzyme

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The structure of enzymes Coenzymes can be considered as an integral part of the enzyme molecule. These are organic substances, among which there are: nucleotides (ATP, UMP, etc.), vitamins or their derivatives (TDP - from thiamine (B1), FMN - from riboflavin (B2), coenzyme A - from pantothenic acid (B3), NAD etc.) and tetrapyrrole coenzymes - hemes. The functions of the prosthetic group are as follows: participation in the act of catalysis, contact between the enzyme and the substrate, stabilization of the enzyme molecule in space.

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Enzymes have 2 centers: the Active center and the Allosteric center. Structure of enzymes The active center (ACS) is a relatively small region located on the surface of the enzyme molecule, which is directly involved in catalysis. It consists of a unique combination of amino acid residues, ensures connection with the substrate and its further transformation. In ACP, they are distinguished: Substrate-binding center - a site that is responsible for complementary binding of the substrate and the formation of an enzyme-substrate complex. Catalytic center - directly involved in chemical reactions with the substrate.

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An allosteric center is a combination of amino acid residues on the surface of an enzyme to which low molecular weight compounds (effectors) bind, the molecules of which differ from the substrates. The addition of an effector changes the tertiary structure and, accordingly, the configuration of ACP, thereby causing a decrease (inhibitors) or increase (activators) in activity. Enzymes that are affected by effectors are called allosteric. The structure of enzymes

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The structure of enzymes A substance whose chemical transformation is catalyzed by an enzyme is called a substrate

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Substrate is a substance on which an enzyme acts. The enzyme and substrate must fit each other “like a key to a lock.” The principle of enzyme action

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The act of catalysis consists of three successive stages. 1. Formation of an enzyme-substrate complex during interaction through the active center. 2. Binding of the substrate occurs at several points in the active center, which leads to a change in the structure of the substrate and its deformation due to changes in the bond energy in the molecule. This is the second stage and is called substrate activation. In this case, a certain chemical modification of the substrate occurs and it is converted into a new product or products. 3. As a result of such a transformation, the new substance (product) loses the ability to be retained in the active center of the enzyme and the enzyme-substrate, or rather, enzyme-product complex dissociates (breaks up). Types of catalytic reactions: A+E = AE = BE = E + B A+B +E = AE+B = ABE = AB + E AB+E = ABE = A+B+E, where E is the enzyme, A and B - substrates or reaction products. Mechanism of action of enzymes

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Enzymes have the properties of proteins, but also have features: 1. Dependence on pH 2. Dependence on temperature 3. High specificity of action 4. Ability to regulate – i.e. may be influenced by activators or inhibitors Enzymes or enzymes are designated by the letter E

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The optimum pH for most enzymes is 6.0-8.0. This is the pH value at which the enzyme exhibits maximum activity. Hydrogen ions can change the degree of ionization of the substrate, product, and enzyme. The optimum temperature for most enzymes is 38-40C; at 41-42C thermal denaturation occurs. When the temperature increases by 10C, the rate of the enzymatic reaction increases by 2 times. 1. Dependence on pH 2. Dependence on temperature Properties of enzymes

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The specificity of the action is determined by the structure of the active center of the enzyme and lies in the fact that each enzyme catalyzes the transformation of one substrate or a group of substrates that are similar in structure. 3. High specificity of action Properties of enzymes

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Properties of enzymes There are several types of specificity. Stereochemical substrate specificity - the enzyme catalyzes the conversion of only one stereoisomer of the substrate. For example, fumarate hydratase catalyzes the addition of a water molecule to the multiple bond of fumaric acid, but not to its stereoisomer, maleic acid. Absolute substrate specificity - the enzyme catalyzes the conversion of only one substrate. For example, urease catalyzes the hydrolysis of only urea. Group substrate specificity - the enzyme catalyzes the transformation of a group of substrates of similar chemical structure. For example, alcohol dehydrogenase catalyzes the conversion of ethanol and other aliphatic alcohols, but at different rates.

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Properties of enzymes 4. Ability to regulate Influence on the activity of enzymes by activators and inhibitors. Factors that increase enzyme activity include metal cations and some anions. Most often, enzyme activators are cations Mg2+, Mn2+, Zn2+, K+ and Co2+, and among anions - Cl-. Cations act on enzymes in different ways. In some cases, they facilitate the formation of the enzyme-substrate complex, in others they facilitate the attachment of the coenzyme to the apoenzyme, or they attach to the allosteric center of the enzyme and change its tertiary structure, as a result of which the substrate and catalytic centers acquire the most favorable configuration for catalysis.

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Inhibitors inhibit the action of enzymes. Inhibitors can be both endogenous and exogenous substances. The mechanisms of the inhibitory action of various chemical compounds are varied.

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Enzymes involved in the synthesis of proteins, nucleic acids and energy metabolism enzymes are present in all cells of the body. But cells that perform special functions also contain special enzymes. Thus, the cells of the islets of Langerhans in the pancreas contain enzymes that catalyze the synthesis of the hormones insulin and glucagon. Enzymes that are characteristic only of the cells of certain organs are called organ-specific: arginase and urokinase - liver, acid phosphatase - prostate. By changing the concentration of such enzymes in the blood, the presence of pathologies in these organs is judged. In a cell, individual enzymes are distributed throughout the cytoplasm, others are embedded in the membranes of mitochondria and the endoplasmic reticulum; such enzymes form compartments in which certain, closely interconnected stages of metabolism occur. Many enzymes are formed in cells and secreted into anatomical cavities in an inactive state - these are proenzymes. There are also isoenzymes - enzymes that differ in molecular structure, but perform the same function. Distribution of enzymes in the body

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Enzymes are widely used in the light, food and chemical industries, as well as in medical practice. In the food industry, enzymes are used in the preparation of soft drinks, cheeses, canned food, sausages, and smoked meats. In animal husbandry, enzymes are used in the preparation of feed. Enzymes are used in the production of photographic materials. Enzymes are used in the processing of oats and hemp. Enzymes are used to soften leather in the leather industry. Enzymes are included in washing powders and toothpastes. In medicine, enzymes have a diagnostic value - the determination of individual enzymes in a cell helps to recognize the nature of the disease (for example, viral hepatitis - by the activity of the enzyme in the blood plasma); they are used to replace the missing enzyme in the body. Application of enzymes

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Tests “Enzymes” 1. Enzymes are: A) regulators; B) catalysts; B) substrate activators; D) carriers of substances through the membrane; D) nerve impulse mediators. 2. Enzymes can only consist of: A) protein; B) protein and non-protein part; B) nucleotides; D) low molecular weight nitrogen-containing organic substances; D) lipids and carbohydrates. 3. A coenzyme is: A) an easily separated protein part of a complex enzyme; B) non-separable non-protein part of a complex enzyme; B) the protein part of a complex enzyme; D) non-protein part of a simple enzyme; D) a loosely bound non-protein part of a complex enzyme. Consolidating new material

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4. A prosthetic group is: A) the protein part of a complex enzyme; B) enzyme structure stabilizer; B) activator of a complex enzyme; D) non-protein part tightly bound to the enzyme; D) part of the enzyme that forms the catalytic center. 5. What is the name of the non-protein part of a complex enzyme responsible for catalysis? A) Coenzyme; B) Apoenzyme. 6. What class do enzymes belong to that catalyze reactions of transfer of functional groups and molecular residues from one molecule to another? A) Hydrolases; B) Transferases; B) Oxidoreductases; D) Isomerases.

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Homework 1. Creative task: prepare a presentation. 2. Abstract on the topic “Areas of application of enzymes”