Here is a compilation of term papers on ‘Enzymes’. Find paragraphs, long and short term papers on ‘Enzymes’ especially written for school and college students.
Term Paper on Enzymes
Term Paper Contents:
- Term Paper on the Introduction to Enzymes
- Term Paper on the Historical Evolution of Enzymes
- Term Paper on the Occurrence and Distribution of Enzymes
- Term Paper on the Classification of Enzymes
- Term Paper on the Activation Energy and Transition State of Enzymes
- Term Paper on the Nomenclature of Enzymes
- Term Paper on the General Properties of the Enzymes
- Term Paper on the Common and Distinct Features in Enzymes and Non-Enzymic Catalysts
- Term Paper on the Characterization of Individual Enzyme Groups
- Term Paper on the Quaternary Structure of Enzymes
Term Paper # 1. Introduction to Enzymes:
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Enzymes are catalysts that increase the rate of a chemical reaction without being changed themselves in the process. In the absence of an enzyme, the reaction may hardly proceed at all, whereas in its presence the rate can be increased up to 107-fold. Enzyme-catalyzed reactions usually take place under relatively mild conditions (temperatures well below 100°C, atmospheric pressure and neutral pH) as compared with the corresponding chemical reactions.
Enzymes are also highly specific with respect to the substrates that they act on and the products that they form. In addition, enzyme activity can be regulated, varying in response to the concentration of substrates or other molecules. Nearly all enzymes are proteins, although a few catalytically active RNA molecules have been identified.
Term Paper # 2. Historical Evolution of Enzymes:
Earlier the agents causing fermentation of sugars were named as ferments. Pasteur working on microorganisms concluded that fermentation and similar processes could be performed only by living cells. This concept was later disputed by J. Liebig who proposed that fermentation could take place even in the absence of living cells. Therefore, a distinction was made between organized ferments present in cells and unorganized ferments that were not associated with microorganisms.
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J.J. Berzelius named the biological agent as ‘diastase’ which is known today as amylase capable of converting starch from malt extract into sugar. The term enzyme (‘in yeast’) was proposed by Kühne to distinguish enzyme from organized and unorganized ferments.
Term Paper # 3. Occurrence and Distribution of Enzymes:
Enzymes occur in all living cells but not all enzymes are found in all the cells. The enzymes catalyze a wide variety of biochemical reactions many of which are localized in specific organs or are peculiar to certain species of plant or animal life. Thus, for example, pepsin is produced only in the cells of gastric mucosa and trypsin only in the pancreas. In the plant world lipases are not generally distributed but are found chiefly in plants that produce oilseeds.
A few of the enzymes are present in most forms of life. For example, catalases and peroxidases are widely distributed in all higher plants and animals.
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The amount of enzymes may be different in different tissues. For example, resting seeds have low activity of amylases and proteinases while the germinated seedlings have more activity. In some fruits, enzymes are concentrated near pit. Some enzymes are also organelle-specific.
Term Paper # 4. Classification of Enzymes:
All the enzymes are classified into six groups; of these, each is assigned a definite number – 1. Oxidoreductases; 2. Transferases; 3. Hydrolases; 4. Lyases; 5. Isomerases; 6. Ligases (synthetases).
The name of the group indicates the type of the chemical reaction catalyzed by enzymes. Therefore, there are six major types of enzymic-reactions. The groups are divided into subgroups; the latter are further subdivided into subgroups. The number of subgroups in a group varies, as well as the number of subgroups in a subgroup.
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The subgroup specifies the enzymic action in giving a general characterization of the nature of the substrate’s chemical moiety subject to attack by the enzyme. The subgroup further concretizes the enzymic action by defining the nature of the substrate bond to be cleaved, or the nature of the acceptor that is involved in the reaction.
According to the numerical classification system, each enzyme receives a four-part number whose numerals are separated by a dot:
All new enzymes are classified only in accordance with the recommendations of the Committee on Enzyme Nomenclature of the International Union of Biochemistry.
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Term Paper # 5. Activation Energy and Transition State of Enzymes:
The energy changes that take place during the course of a particular biochemical reaction. In all reactions there is an energy barrier that has to be overcome in order for the reaction to proceed. This is the energy needed to transform the substrate molecules into the transition state—an unstable chemical form partway between the substrates and the products. The transition state has the highest free energy of any component in the reaction pathway.
The Gibbs free energy of activation (∆Gǂ) is equal to the difference in free energy between the transition state and the substrate. An enzyme works by stabilizing the transition state of a chemical reaction and decreasing ∆Gǂ. The enzyme does not alter the energy levels of the substrates or the products. Thus an enzyme increases the rate at which the reaction occurs, but has no effect on the overall change in energy of the reaction.
Free Energy Change:
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The change in Gibbs free energy (∆G; kJ mol-1) dictates whether a reaction will be energetically favourable or not. Fig, 13.1 shows an example where the overall energy change of the reaction makes it energetically favourable (i.e. the products are at a lower energy level than the substrates and ∆G is negative). It should be noted that ∆G is unrelated to ∆Gǂ.
The ∆G of a reaction is independent of the path of the reaction, and it provides no information about the rate of a reaction since the rate of the reaction is governed by ∆Gǂ. A negative ∆G indicates that the reaction is thermodynamically favourable in the direction indicated (i.e. that it is likely to occur spontaneously), whereas a positive ∆G indicates that the reaction is not thermodynamically favourable and requires an input of energy to proceed in the direction indicated. In biochemical systems, this input of energy is often achieved by coupling the energetically unfavourable reaction with a more energetically favourable one (coupled reactions).
It is often convenient to refer to ∆G under a standard set of conditions, defined as when the substrates and products of a reaction are all present at concentrations of 1.0 M and the reaction is taking place at a constant pH of 7.0. Under these conditions a slightly different value for ∆G is found, and this is called ∆G0‘.
An example of an energetically favourable reaction which has a large negative DG0‘ and is commonly used to drive less energetically favourable reactions is the hydrolysis of ATP to form ADP and free Pi:
It is well known that highly complex synthetic and breakdown reactions take place much more rapidly and easily by the living organism. In the absence of the cell these chemical reactions would proceed too slowly. The principal agents which participate in the precise and orderly transformations and regulation of the chemical reactions in the cell belong to a group of proteins named enzymes.
An enzyme is a protein that is synthesized in a living cell and catalyzes or speeds up a thermodynamically possible chemical reaction. The enzyme in no way modifies the equilibrium constant (Keq) or the free energy change (∆G) of a reaction.
Term Paper # 6. Nomenclature of Enzymes:
At present, it is believed that the cell contains about 104 enzyme molecules capable of catalyzing over 2000 various reactions. There are 1800 enzymes known to date. About 150 enzymes have been isolated in the crystalline form. The preparation of enzymes as purified crystals is necessary for studying mechanistic intricacies of enzymic catalysis as well as in laboratory experiments and industrial applications.
At the earlier period, there has been no clearly defined systematics in the classification and nomenclature of enzymes – the name conferred upon each newly discovered enzyme usually originated in its explorer’s imagination. The French microbiologist and biochemist Duclaux made first attempts to introduce a practical rule for naming enzymes. According to this rule, the trivial (working) name for an enzyme was made up of the ending -ase added to the name of the substrate subject to the action of the enzyme in question – for example, saccharose + ase = saccharase.
Official Nomenclature of Enzymes:
The currently accepted official nomenclature of enzymes are based on the following principles.
Nomenclature of Enzymes:
At the present time, two nomenclature systems are accepted for enzymes; accordingly, an enzyme is’ given a trivial name and systematic name. The trivial name is composed of the name of the substrate involved, the type of the reaction catalyzed, and the ending -ase.
For example:
lactate + dehydrogenation + ase = lactate dehydrogenase
A number of long-known enzymes have retained their traditional names- pepsin, trypsin, chymotrypsin, etc.
The systematic name for an enzyme is constructed in a more complicated manner. It is made up of the names of substrates of the chemical reaction catalyzed by the enzyme, the name of the type of the catalyzed chemical reaction, and the ending-ase.
For example, the systematic name for the enzyme lactate dehydrogenase is written as:
The systematic names are given to the explored enzymes only.
Term Paper # 7. General Properties of the Enzymes:
Enzymes possess the following general properties.
i. Substrate Specificity:
Unlike the inorganic catalysts, enzymes mostly act only on some specific substrate or specific type of substrates and convert them into certain specific products.
ii. Temperature and pH Optima:
Every enzyme has got an optimum temperature and an optimum pH at which it shows its maximum activity. An increase in temperature increases the enzyme activity but at the same time also increases enzyme denaturation.
The temperature at which these two processes balance each other showing maximum activity is known as its optimum temperature. Enzyme activity decreases as a result of decrease in temperature, but simultaneously, the rate of denaturation also decreases. Thus at lower temperatures, enzyme activity can be better preserved for longer periods.
A pH at which maximum activity is observed with least destruction of the enzyme is known as its optimum pH. Different enzymes hive got specific optimum pH values which usually fall in the pH range of 5.0 to 9.0. However, a few enzymes such as pepsin, have their optimum pH values outside this range. Extremely high or low pH values result into extensive denaturation of the enzyme proteins and hence rapid loss of enzyme activity.
iii. Effect of Substrate Concentration:
For a given amount of the enzyme, the rate of reaction is influenced by the concentration of the substrate. If the substrate concentration is gradually increased keeping the enzyme concentration constant, the rate of reaction also increases but after attaining a certain level, increase in the substrate concentration does not increase the reaction rate.
This is due to the fact that enzyme molecules possess a limited number of active sites to which the substrate molecules get attached. Increase in the concentration of the substrate goes on saturating the active sites. A stage comes when all the active sites existing in a particular amount of enzyme are saturated.
Increase in the, substrate concentration increases enzyme activity upto reaching such a stage, but after attaining the saturation point, excess substrate does not find any active site free on the enzyme molecule, and hence, excess substrate is not acted upon by the enzyme till the active sites become free. Hence, the rate of enzyme activity remains unaffected after attaining the saturation point. In certain cases, further increase of substrate concentration might inhibit the enzyme activity.
iv. Denaturation:
If the natural conditions are changed, the enzyme proteins undergo denaturation which is accompanied by a parallel loss of enzymic activity. Enzymes may be denatured by acids, high salt concentrations, heavy-metal salts, alkaloid reagents, or ultraviolet light treatment.
The loss of enzymic activity on denaturation is due to certain changes in secondary, tertiary and quaternary structures of the enzyme protein which involve partial or complete breakdown of weak ionic or nonpolar bonds responsible for maintaining natural structure of the enzyme.
v. Activation:
Most of the enzymes can be activated by addition of certain specific agents. In the absence of such factors, enzymes become inactive or sluggish. Such agents are known as enzyme activators.
vi. Inhibition:
Enzyme activity may be inhibited by addition of some specific agents which are known as inhibitors.
Term Paper # 8. Common and Distinct Features in Enzymes and Non-Enzymic Catalysts:
Enzymes and non-biological catalysts, in obeying the general laws of catalysis, share the following common features:
i. They catalyze energetically feasible reactions only.
ii. They never alter the reaction route.
iii. They do not affect the equilibrium of a reversible reaction, but rather accelerate its onset.
iv. They are never consumed during the reaction. Therefore, a cellular enzyme functions until it becomes impaired for one or another reason.
However, enzymes exhibit a number of features that distinguish them from non-biological catalysts. These distinctions are due to structural specificities of the enzymes which are complex protein molecules.
1. The rate of enzymic catalysis is much superior to that of non-enzymic catalysis. It follows there from that enzymes lower the activation energy of reactions to a greater extent as compared with non-biological catalysts. For example, the activation energy for the reaction of hydrogen peroxide decomposition,
H2O2 → H2O + 1/2 O2
is equal to 75.3 kJ/mol. Under catalyst-free conditions, the spontaneous decomposition of H2O2 proceeds at such a slow rate that the evolution of oxygen as gaseous micro bubbles escapes visual observation. Addition of an inorganic catalyst (iron or platinum) reduces the energy of activation to 54.1 kJ/mol, and the reaction rate becomes accelerated by a factor of few thousands, which can easily be observed by visible evolution of oxygen bubbles.
The enzyme catalase, which can decompose H2O2, produces more than a fourfold decrease in the energy of activation (to 80 kJ/mol) and a 109-fold acceleration of the peroxide decomposition reaction. The reaction takes such a vigorous course that the solution appears “effervescent” with evolving oxygen.
A single enzyme molecule can, at normal temperature (37°C), catalyze 103 to 108 molecules per minute. Such high rates are unattainable in the catalysis effected with non-biological catalysts.
2. Enzymes exhibit a high specificity. There are enzymes that act selectively on only one stereo isomer of a compound, whereas platinum, for example, is employed as catalyst in a number of reactions. The high specificity of enzymes enables them to direct metabolic processes to strictly defined channels.
3. Enzymes catalyze chemical reactions under “mild” conditions, i.e. at normal pressure, low temperature (about 37°C), and pH close to that of the neutral medium. This behaviour differentiates them from other catalysts active at high pressure, extreme pH values, and high temperature.
Enzymes, because of their proteinic nature, are susceptible to temperature variations (i.e. are thermolabile) and to the change of medium pH.
4. Enzymes are catalysts with controllable activity, the behaviour never encountered in non-biological catalysts. This unique property in enzymes allows changing the rate of metabolism in the organism depending on the environmental conditions, i.e. adapting the metabolic activity to the action of various factors.
5. The rate of an enzymic reaction is proportional to the amount of enzyme, while no strictly defined relationship of this kind is found in non-biological catalysts. Therefore, the short supply of an enzyme in the living organism signifies a lower rate of metabolism and, on the contrary, the additional production of an enzyme is one of the adaptive routes for the organism cells.
Term Paper # 9. Characterization of Individual Enzyme Groups:
Oxidoreductases are enzymes that catalyze redox reactions. Oxidoreductases are subdivided into 17 subgroups. The substrate subject to oxidation with oxidoreductases is regarded as a hydrogen donor. For this reason, the enzymes in this group are called dehydrogenases, or, less commonly, reductases. If O2 acts for an acceptor, the term oxidase is employed; if during oxidation, an O2 molecule is directly incorporated into the substrate, the term oxygenase is used.
The systematic name for an enzyme of this group is made up as donor; acceptor-oxidoreductase, for example:
Oxidoreductases constitute a widespread group encompassing about 480 enzymes. They play a decisive role in the energy metabolism.
Transferases are enzymes that catalyze reactions of transfer of various moieties from one substrate (donor) to another (acceptor). Transferases are subdivided into 8 subgroups, depending on the structures of the moieties they transfer. The enzymes that catalyze the transfer of methyl groups are called methyl transferases; those that catalyze the amino group transfer are called amino transferases, etc.
In principle, oxidoreductases may be assigned to transferases if the major-route is considered to be a donor-to- acceptor transfer with concomitant oxidation reduction rather than the oxidation-reduction. These enzymes may also be named proton transferases, electron transferases, etc.
Their systematic names are made up after the pattern – acceptor—moiet—L-transferase, or donor—moiety—transferase.
Most commonly, in transferase-catalyzed reactions, the donor is a cofactor containing the moiety to be transferred, for example-
Transferases are of about as much frequent occurrence as oxidoreductases. Transferases are involved in inter-conversion reactions of various compounds, in the synthesis of monomers, in neutralization of native and foreign materials.
Hydrolases are enzymes that catalyze the substrate bond cleavage by adding water. Hydrolases are subdivided into 11 subgroups. The trivial names for hydrolases are made up by adding the ending -ase to the name of substrate. Systematic names must, by convention, contain the term hydrolase.
In principle, hydrolases may be assigned to the transferase group, since hydrolysis may be regarded as a transfer of a specific group from the donor substrate onto a water molecule as acceptor. However, the accepting role of water is considered to be of prime importance for the action of these enzymes; for this reason, they have been singled out as an individual hydrolase group.
For example:
The hydrolase group numbers about 460 enzymes. The hydrolases include digestive enzymes as well as enzymes forming part of lysosomes and other organelles; in the cell, they promote hydrolytic decomposition of large biomolecules into simpler ones.
Lyases are enzymes that catalyze bond-cleaving reactions in a substrate without oxidation or addition of water. Lyases are subdivided into four subgroups.
The systematic name for a lyase is made up after the pattern substrate-moiety-lyase. The trivial name of a lyase is indicative of specific participation of the moiety in reaction, for example – carboxylase, addition of a carboxyl moiety; dehydratase, elimination of a water molecule from the substrate, etc. If it is essential to emphasize the formation of a substrate from two simpler substrates, the term synthase (not to be confused with synthetase) is employed, for example, citrate synthase.
An example of a lyase-catalyzed reaction is shown below:
Lyases are a more rare group of enzymes (about 230), which participate in reactions of synthesis and decomposition of intermediary metabolites.
Isomerases are enzymes that catalyze structural rearrangements within a single molecule. Isomerases are subdivided into five subgroups.
They are given names according to the type of the isomerization reaction they are involved in, for example, mutases, tautomerases, racemases, epimerases, isomerases, etc. –
The isomerases are a relatively small group of enzymes (slightly over 80) that play a decisive role in the restoration of molecular biological activity and in the switchover of metabolites to various metabolic routes. Ligases (synthetases) are enzymes that catalyze the addition of two molecules using the energy of phosphate bond. ATP or other nucleoside phosphates serve as energy sources in the synthetase-catalyzed reactions.
For example:
The ligases (of total number of about 80) are subdivided into five subgroups.
Term Paper # 10. Quaternary Structure of Enzymes:
Extracellular enzymes, such as lysozyme, ribonuclease and the proteases, tend to be small and robust, stability being very important in the extracellular environment; they are usually composed of one polypeptide chain, with intramolecular disulphide bonds. Intracellular enzymes are often much larger, with molecular weights in the range 101 – 106, and are composed of subunits, which are non-covalently linked.
Subunits may be identical or non-identical usually there is only one active site on each polypeptide chain, although there are exceptions to this-DNA polymerase I, for example, has a single chain with three different activities. Even when enzymes are composed of several subunits there may be no apparent interaction between them – aldolase, for example, has four identical, non-interacting subunits, which retain their activity when separated.
However, interaction between identical or similar subunits can lead to cooperativity in substrate binding – this alters the shape of the substrate binding curve, and is an important feature in the regulation of some enzymes.
Other enzymes are composed of non-identical subunits, each having a different function. Protein kinase has two types, one containing the active site, the other the binding site for the regulator, cAMP. The 2-oxoacid dehydrogenases are really multi-enzyme complexes, as they contain five types of subunit, catalysing different reactions in the sequence: transfer of the substrate between associated subunits is more rapid than diffusion between separate enzyme molecules, and unstable intermediates can be transferred directly from one prosthetic group to another.
Other examples of multi-enzyme complexes are found in the synthesis of pyrimidines and of fatty acids. The fatty acid synthetase complex catalyses seven sequential reactions – in E. coli this enzyme has seven different subunits, non-covalently associated, but in higher animals it has only two very large polypeptides, one of which has three different activities, the other four.
Such enzymes appear to have evolved by fusion of the genes coding for separate proteins, to produce a single gene coding for a protein with several different active sites. The protein is folded into a series of domains, each with a different function; sometimes these can be separated, without loss of activity, after proteolysis to break the peptide chain which connects them.
Isoenzymes:
Sometimes multiple molecular forms of an enzyme are found – these may differ in physical and kinetic properties, and are called isoenzymes. Different isoenzymes may have a different location within the cell: both malate dehydrogenase and glutamate- oxaloacetate transaminase exist in cytoplasmic and mitochondrial forms, which catalyse the same reaction but have no close structural relationship. In other cases different isoenzymes are found in different tissues, and these are the products of related genes.
Lactate dehydrogenase is a tetramer, composed of subunits (mol. wt 35000) which may be of two types, called H and M. These combine to produce five different isoenzymes – H4, H3M, H2M2, HM3 and M4 (also known as LDH, LDH2… LDH5). The H4 form predominates in heart, M4 in skeletal muscle and liver – other tissues contain various proportions of the five isoenzymes. The H and M subunits have different kinetic properties, and those of the isoenzymes vary according to the subunit composition.
They may be separated by electrophoresis in starch or agarose gels, and detected by a stain for LDH activity, in which an artificial electron carrier phenazine methosulphate (PMS) reoxidizes NADH generated by enzyme activity, reducing a tetrazolium dye and so staining the gel H4 (LDH,) is the most acidic of the five isoenzymes, and runs closest to the anode – M4 (LDH,) runs closest to the cathode.
The tissue damage that occurs in certain disease states results in selective increases in particular isoenzymes in the serum. Thus myocardial infarction (increase in LDH„ and to a lesser extent LDH2), liver disease (LDH5). Duchenne’s muscular dystrophy (LDH, and LDH2 equally) and diseases of the lungs, leukaemia, pericarditis and viral infections (LDH3 and LDH4) can all be diagnosed by examination of serum isoenzymes.
Creatine kinase has two subunits, which may be of two types, B and M, generating three isoenzymes BB (CK2 found in brain, lung and bowel), BM (CK2, found in myocardium) and MM (CK3, found in skeletal muscle and myocardium). Electrophoretic measurement of creatine kinase isoenzymes is also used in the diagnosis of disease states; other isoenzymes which may be measured include those of glutamate-oxaloacetate transaminase, and acid- and alkaline-phosphatases.