Enzyme Nature, Structure and Function as Catalysts for Cellular Biochemical Reactions - Essay Example

ENZYME FUNCTION AND STRUCTURE ENZYME NATURE, STRUCTURE AND FUNCTION AS CATALYSTS FOR CELLULAR BIOCHEMICAL REACTIONS 18th May, 2013 Introduction and definition to metabolic enzymes Enzyme activity and function Enzyme environment and favourable physiological conditions required for its function Conclusion References Introduction to enzymes Enzymes are protein complexes secreted and working in the intracellular environment of living organisms, with the role of catalyzing biochemical reactions. Almost all biochemical processes in the cells requires energy supply in order to facilitate amplified rates of biochemical reactions at phases that can sufficiently support the life of the organism as commonly referred to basal metabolic rates. Usually enzymes works on specific metabolic substrates through a ‘lock and key hypothesis’ to generate useful products required by cells especially ATP as a source of body energy. The biological catalysts increases cellular biochemical reaction rates by causing a general decrease of the activation energy (Ea) leading to easy and faster reach of reaction thresholds. Generally the structure of these enzymes is kept constant after the end of their particular activity and this allows efficient activity in this cellular environment (Theresa Philips, 2013). However there is a narrow range of environmental conditions which facilitate this occurrence, and they include a specific PH, temperature, and other physical conditions. Also other external factors may have either a direct or an indirect effect to enzymatic function and nature. These include substrate, product and enzyme concentrations, intracellular pressure, as well presence of both competitive enzyme inhibitors and non-competitive enzyme inhibitors. Others have been found to facilitate reverse reactions through reduction of activation energies of particular biochemical reactions. Enzymes are specific in nature, and in normal circumstances they work on specific biomolecules in the cellular environment called substrates to form useful components in the cell known as products. The figure 1 below shows a representation of enzyme specificity to metabolic substrates through a key and lock hypothesis, to form an enzyme-substrate complex before forming the reaction products. Figure 1: Enzyme Lock and key hypothesis (RSC, 2004) In their cellular activity as biological catalysts most of body enzymes require other compounds known as the 'cofactors' to enhance the efficiency in their catalytic activity exertion. This entire component or the active complex is referred to as the holoenzyme; and it includes the apoenzyme which is a protein portion and a cofactor which is a coenzyme, a prosthetic group or a metal-ion-activator. Both the coenzyme part which is non-protein and the prosthetic part which is an organic substance, are dialyzable thermostatically stable and loosely attached organic substance to the protein component (Dunaway-Mariano D, 2008). Metal-ion activators includes K+, Fe+++, Fe++, Co++, Cu++, Mn++, Zn++, Mg++, Ca++, and Mo+ and these are very important in the biological catalytic reactions. Their mode of action is usually selective to the specific biomolecules which they act upon, through a scientific mechanism referred as 'Lock and Key Hypothesis'. In this mechanism the substrates binds the enzymes in their active sites, and thus lowering the activation energy for the biochemical reaction involved. This results to an increase in the rate of such biological reaction up to a million fold, and this is because of a faster reach of its equilibrium. The active site of the enzyme forms a temporal bond with the substrate undergoing that biochemical reaction to form the product, after the enzyme has disangaged itself from the enzyme substrate-complex. The active site is the part of an enzyme or antibody where the chemical reaction occurs, and this chemical structure or bond gives each enzyme its special character of specificity. Generally a narrow range of physiological conditions should be maintained in the cellular environment so as to allow retaining of enzyme structure and nature outside which the enzymes becomes inactive or may be denatured altogether (Agarwal PK, 2005). Enzyme activity and function Enzymes are high molecular weight compounds made up mainly of chains of amino acids joined together by peptide bonds. Enzymes may be denatured and precipitated with salts, solvents and other reagents depending on their immediate environment. They have molecular weights ranging from 10,000 to 2,000,000, and these biochemical catalysts are very essential in facilitating life as almost all of essential cellular processes require an enzymatic presence to increase the rates of reaction (Dunaway-Mariano D, 2008). By binding with the substrate in its active site, the enzyme forms a complex known as an enzyme-substrate complex which has high potentiality of forming useful products. This occurs when enzymes lower the activation energy for their specific biochemical reactions and thus enhancing a very dramatic increase in the rate of reaction. The equilibrium of such reactions becomes easily achieved, leading to a faster progress of forming the products. This is because a lot of energy is needed in any biochemical reaction to necessitate achievement of the equilibrium which acts as an action potential. Without reaching the action potential or equilibrium of any particular biochemical reaction, under the all or none law the reaction cannot progress to give expected products. Therefore enzymes are necessary components of biochemical reactions to sustain life in all living organisms. This is to the fact that they lower the activation energy of their specific biochemical reactions and this leads to a dramatic increase in their rates of forming essential cellular products which sustains life. The enzyme-substrate complex after the completion of a given biochemical reaction dissociates and the products are liberated. From the past studies, it has been found that enzymes only catalyse these cellular biochemical reactions and they do not form part of the product generated. The substrates form products without consuming or destroying the nature and structure of their specific enzymes, and this allows the enzymes to be reused for the next similar cellular biochemical reactions. Other than the internal and external factors, these biological catalysts do not alter the equilibrium of biochemical reactions (Theresa Philips, 2013). Therefore for their efficient function, enzymes need a narrow range of external as well as internal physiological conditions such as temperature, pressure, pH, inhibitors and activators and substrate or enzyme concentrations. Conditions affecting enzyme function Temperature This is the degree of hotness or coldness of a given medium (specifically the cellular environment), in a numerical scale of for instance degrees Celsius measured by a thermometer. Generally the rate of any biochemical reaction increases with any raise in temperature. This is by the fact that as temperature increases, the heat energy gained by biomolecules enhances their kinetic energy status (RSC, 2004). Increased kinetic energy results to increased frequency of collisions of the participating biomolecules or substrates in that particular cellular biochemical reaction as seen by the figure 2 below. Figure 2: The effect of temperature on the rate of reaction (RSC, 2004) But as the enzymes are proteinic in nature as we have earlier stated, increased temperatures beyond the physiological value, which is about 37.5 degrees Celsius, the enzymes becomes denatured. This leads to loss of that specific nature and structure, particularly the active site and this results to lack of formation of enzyme-substrate complex. The biochemical reactions which will be without a lowered activation energy, reaching of its equilibrium becomes prolonged hence essential products are slowly formed (Theresa Philips, 2013). This may be worsened by further increase in temperature, as these proteins or their complexes becomes denatured as the essential cellular biochemical reactions cannot take place, and the whole organism may die. This is why living organisms may not survive under extremely high temperature conditions, without any significant adaptations. The distorted nature and structure of enzymes after denaturation, cannot allow the normal functions of these biological catalysts in their particular cellular biochemical reaction. On the other hand, too low temperature may cause inactivity of the enzymes, and this is based on the low kinetic energy of the biomolecules. Low rates of biomolecules collisions or lack of them, causes low rates of reaction as the enzyme-substrate complexes are slowly formed (Tousignant A, and Pelletier JN, 2004). Therefore there is an optimum narrow value of temperature required by every enzyme to perform its normal functions. Despite other enzymes working under lower temperatures, most of these biological catalysts work best around the physiological temperature 37.5 (35-40) degrees Celsius. Low or high temperatures cause inactivity and subsequent denaturation of these enzymes proteinic structure and this interfere with their specific functions in catalyzing the cellular biochemical reactions. Enzymes such as B. licheniformis amylase, endoglucanase and lipase have adaptations to high temperature conditions, and this can sometimes be applied in industrial processes such as bio-refinimg (Pemilla et al, 2007). The pH value This refers to the alkalinity or acidity of the enzyme environment (especially the intracellular) and it is a numerical scale of one to fourteen using a pH meter. Enzymes are protein complexes and their biochemical components include specific amino acids. Changes in acidity or alkalinity of a particular enzyme environment through changes in pH, results to a change in their charges since these environments alkalinize or acidify these bio-catalysts (Theresa Philips, 2013). Acidity and alkalinity usually causes interference with enzyme structure, through specific charge interference and this affects the structure and shape of their active sites. This relatively affects the formation of enzyme-substrate complex negatively, and this decreases the rates of specific cellular biochemical reactions. Research has indicated that most enzymes favorably function well in a physiological PH of 7.5 and this is where their nature and structure remains most stable (Theresa, 2013). However some enzymes have media specificity, that is they work well in acidic or alkaline environments with decreased or increased pHs respectively depending on their biochemical environment. This is because as the pH of the enzyme environment changes, there is a corresponding in the basic nature and structure of the particular biochemical catalyst. This usually causes a failure forming a proper key and lock hypothesis complex called enzyme-substrate, since the active site of the enzyme do not bind to its specific substrate due to distorted structure. Generally this affects the rate at which these cellular biochemical reactions occur, and thus the rates at which essential cellular products are formed (RSC, 2004). Also this interferes with the nature and structure of active sites, may result to an ultimate stoppage in the formation of enzyme-substrate complexes and thus cellular biochemical reactions as shown in the figure 3 below. The effect of pH on amino acids is determined by the acidity or alkalinity of the environment. Since amino acids structure of amino acids contains both the carboxylic acid (acid) and the amine (basic) functional groups, the effect of pH is similar as it is effect on bases and acids. There is a dissociation of these functional groups and this alters the structure of enzymes hence the active site and activity (formation of the enzyme-substrate complex). Figure 3: The effect of pH on enzyme activity Enzyme and Substrate concentration Relative increase of enzyme and substrate concentrations in the cellular environment, where the biochemical reactions occurs results to proportional their reactions rates. This correlation applies only up to a state of saturation of enzyme, where more increase of these concentrations does not lead to anymore increase in reaction rates (RSC, 2004). This is because active sites of the enzyme are completely bonded and therefore there is no more site of forming the substrate-enzyme complex and it is shown by the diagram: Figure 4: The effect of plasma enzyme concentration on rate of reaction Figure 5: The effects of substrate concentration on the rate of reaction Inhibitors and activators These are external factors or complexes which compete with the enzyme for the active site of the specific substrate, and they can be either activators or inhibitors which may be competitive or non-competitive to the enzyme. Competitive inhibitors have similar structure as compared to the substrate and binds to the active site of the enzyme to for an inhibitor-enzyme complex which do not allow formation of the enzyme-substrate complex hence stopping the specific biochemical reaction. On the other hand non-competitive inhibitors decrease the rates of biochemical reaction, and this is achieved by interfering the shape and structure of the active site in the enzyme nature and this changes or alters structure of the enzyme’s active site reacting with the active site. Activators comprise all other external factors which facilitate the efficient formation of any particular enzyme-substrate complex and this ultimately increases the rate of cellular biochemical reactions. Amino acid dissociation is summarized by the equation below; RCOOH RCOO -1 + H +1 R-NH3 +1 R-NH2 + H +1 References Agarwal PK 2005, 'Role of protein dynamics in reaction rate enhancement by enzymes', J. Am. Chem. Soc. vol. 127, no. 43, pp. 15248–15256. Dunaway-Mariano D 2008, 'Enzyme function discovery', Structure, vol.16, no.11, pp. 1599–600. Pemilla Turner, Gashaw Mamo, and Eva Nordberg Karlsson (2007), Potential and Utilisation of Thermophiles and Therostable enzymes in Biorefining Royal Society of Chemistry-RSC 2004, 'Enzyme structure and Function', Chemistry for Biologists, viewed 17th March 2013, http://www.rsc.org/Education/Teachers/Resources/cfb/enzymes.htm Tousignant A, Pelletier JN 2004, 'Protein motions promote catalysis', Chem Biol, vol. 11, no. 8, pp. 1037–1042. Read More

Their mode of action is usually selective to the specific biomolecules which they act upon, through a scientific mechanism referred as 'Lock and Key Hypothesis'. In this mechanism the substrates binds the enzymes in their active sites, and thus lowering the activation energy for the biochemical reaction involved. This results to an increase in the rate of such biological reaction up to a million fold, and this is because of a faster reach of its equilibrium. The active site of the enzyme forms a temporal bond with the substrate undergoing that biochemical reaction to form the product, after the enzyme has disangaged itself from the enzyme substrate-complex.

The active site is the part of an enzyme or antibody where the chemical reaction occurs, and this chemical structure or bond gives each enzyme its special character of specificity. Generally a narrow range of physiological conditions should be maintained in the cellular environment so as to allow retaining of enzyme structure and nature outside which the enzymes becomes inactive or may be denatured altogether (Agarwal PK, 2005). Enzyme activity and function Enzymes are high molecular weight compounds made up mainly of chains of amino acids joined together by peptide bonds.

Enzymes may be denatured and precipitated with salts, solvents and other reagents depending on their immediate environment. They have molecular weights ranging from 10,000 to 2,000,000, and these biochemical catalysts are very essential in facilitating life as almost all of essential cellular processes require an enzymatic presence to increase the rates of reaction (Dunaway-Mariano D, 2008). By binding with the substrate in its active site, the enzyme forms a complex known as an enzyme-substrate complex which has high potentiality of forming useful products.

This occurs when enzymes lower the activation energy for their specific biochemical reactions and thus enhancing a very dramatic increase in the rate of reaction. The equilibrium of such reactions becomes easily achieved, leading to a faster progress of forming the products. This is because a lot of energy is needed in any biochemical reaction to necessitate achievement of the equilibrium which acts as an action potential. Without reaching the action potential or equilibrium of any particular biochemical reaction, under the all or none law the reaction cannot progress to give expected products.

Therefore enzymes are necessary components of biochemical reactions to sustain life in all living organisms. This is to the fact that they lower the activation energy of their specific biochemical reactions and this leads to a dramatic increase in their rates of forming essential cellular products which sustains life. The enzyme-substrate complex after the completion of a given biochemical reaction dissociates and the products are liberated. From the past studies, it has been found that enzymes only catalyse these cellular biochemical reactions and they do not form part of the product generated.

The substrates form products without consuming or destroying the nature and structure of their specific enzymes, and this allows the enzymes to be reused for the next similar cellular biochemical reactions. Other than the internal and external factors, these biological catalysts do not alter the equilibrium of biochemical reactions (Theresa Philips, 2013). Therefore for their efficient function, enzymes need a narrow range of external as well as internal physiological conditions such as temperature, pressure, pH, inhibitors and activators and substrate or enzyme concentrations.

Conditions affecting enzyme function Temperature This is the degree of hotness or coldness of a given medium (specifically the cellular environment), in a numerical scale of for instance degrees Celsius measured by a thermometer. Generally the rate of any biochemical reaction increases with any raise in temperature. This is by the fact that as temperature increases, the heat energy gained by biomolecules enhances their kinetic energy status (RSC, 2004).

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