Properties of Enzyme Proteins that function as living catalysts,called enzymes. Enzymes increase speed of metabolic reactions. Low contamination,low temperature and increased breakdown are only possible with enzymes. Breakdownis increased, with the product made to a great gradation of purity. General Characters:Enzymes have following general characters:Protein Natureof Enzymes: Most of enzymes are globular proteins. some enzymes like ribozymes arenucleic acid in nature. Globular structure of proteins is very significant forproper function of enzymes.

    • Composed of C, H, O and N.Sulphur may also be present.      • One or more polypeptide chains- large number of associated amino acids.

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• Formed on the ribosomes –translation of mRNA during protein synthesis. • Demolished by high temperatureand unfavorable pH.Catalytic Characters:  Enzymes speed up the chemical reactions. Theyare not spent in chemical reaction.

An enzyme cannot start the reaction it canonly increase the speed of a reaction. The competence of an enzyme reaction isexpressed form of turner number. The number for sucrose’s is 105 andfor catalases is 106.  Folded Shape of Enzymes :• The polypeptide chains are closed into aspecific three-dimensional nature. • The correct coiledshape is important for enzyme action ‘tertiary structure’.

 • The shape gives theenzyme special areas known as active sites. • The well-matchedsubstrate molecules bind to the counterpart active site. • Different enzymeshave a differently shaped active site.

• Higher temperatures morekinetic energy, so more collisions  Role of Enzymes in Living Things: Enzymes catalyze allmetabolic reactions. • They lower the activation energy – theenergy input needed to bring about the reaction. • Control the thousandsof different metabolic reactions in a cell and in the organism. • The activity of a cell is resolute by whichenzymes are active in the cell at that time. • Cell activity is altered by removingspecific enzymes and/or manufacturing new enzymes. ActiveSite Theory :”Lock and Key andInduced Fit modal” • The enzyme’s activesite has a shape opposite to the substrate. • The substrate locks into the active site ofthe enzyme. • The active site alters its shape holding thesubstrate more tightly and straining it.

 • An enzyme-substrate complex is formed. • The substrate undergoes a chemical change –a new substance is formed. • The product isreleased from the active site. • The free unaltered active site is ready toreceive fresh substrate.

 Solubility: Enzymes as proteins are soluble in water or weaksalt solution.They are insoluble in non-polar solvent like eather. Molecular weight :Enzymes have high Mw(varying from 10000 -several thousands)Enzymes have buffering capacity:  They are amphoteric molecules i.e. behaveboth as acids and bases.  At pKa they makethe most efficient buffer.

They act as buffer in acid and base solution.Each enzyme has a specific isoelectric pH:    It isthe pH at which the net charge on protein equal to zero –so they do not move inan electric field. It is the pH at which the protein molecule carries equalpositive and negative charges Above PI -negatively charged can move in an    electric field Below PI -positive chargedand can move under an electric field.Denaturation:   When proteins are heated, or subjected to excessesof temperature, high salt, organic solvents e.g, the non-covalent bonds break,changing the native structure to random coil. This unfolding of protein is dueto loss of secondary, tertiary and quaternary structure.

It does not affectprimary structure. Effect of Denaturation: Loss of activity due to loss of shape and active site. Denaturing Factors: •Heat          •Change in pH       •Radiation         •Heavy metals         •Detergents                       •Digestive enzymes      •Urea    •Repeated freezing and the wing Chemical reaction: (i)Xanthroprotoicreaction: Proteins containingphenylalanine end tyrosine—give orange color.(ii)Mallon’sreaction:Proteins containingphenolic(-OH) group of tyrosine—give red color(iii)Sulfate reaction: Proteins containingsulfur amino acids (cysteine) —-give black or grey color(iv)Biuret’sTest:•This is a general testfor all proteins because it O is given by peptide linkage ( C -N) H•The reaction occursbetween protein, sodium hydroxide and copper sulfate giving violet complex.Specificity:  The specific of enzyme is due to primaryamino acids sequence. e.g.

sucrose acts upon sucrose and lactase on milk sugar.•Enzymes are highlyspecific. They are specific for:                                                                                                                                                                                                                                                                                                                                                                                                                     •the reactions they catalyze.                                                                                                                                                •andin their course of reaction, which are called substrates. (a)Absolute specificity: The enzyme can act onlyon one specific substrate.(b)Group specificity:•Broad specificity •Enzyme act on a groupof related substrates. •The substrates have a common group on whichthe enzyme acts: e.

g. -esterase can act on different esters -proteases can acton different protein e.g. of proteases: chymotrypsin, trypsin, pepsin.The specificity is dueto substrate binding site which lies on the enzyme surface -in specification isdue to the specific organization of amino acids in the active site thatparticipate in the bond making and bond breaking.

Thespecification of an enzyme is determined by:(a) Groups of enzymes:(b) Groups of substrate:During enzyme action,there is a temporary combination between enzyme and its substrate formingenzyme by relatively weak forces. This occurs at the active site of the enzyme(most substrates are bound to the enzyme by relatively weak forces.In thisenzyme substrate complex formed .                  E + S          à           ES complex    Activation energy: Is minimum energy that isrequired to start a reaction called activation energy. Enzymes lower theactivation energy. The reaction can take place in the absence of enzyme.

But itneed higher amount of activation energy.Lower the activation energy alsodestroyed the enzyme setrecture.   Product Inhibition:  The accumulation of products ofthe reaction can inhibit the enzyme activity. The effect is very important forcell.

It maintain the concentration of the product in a cell.It also destroyedthe cell setrecture. Allosterism:   Some enzymes have specificallosteric site for binding of certain effecters.

The binding of effecterschange in the structure of enzyme. Allosteric is shown by many enzymes. Sensitivity of Enzyme:  Enzymes are sensitive for following factors:a)      HighTemperature:  b)      Enzymes are sensitive for heat.

Activity ofenzymes increase with the increase of temperature of to 50 degree. The enzymesare denatured at 70 to 100 degree. Such conditions are present in spore and dryseeds.  c)      b)Low Temperature:    d)     Enzymes are also sensitive for lowtemperature. They are inactivated at 0 -10 Degree.At low tempreture enzymesdo not work.

e)      Radiation:  f)       Enzymes are also destroyed by radiation oflower wavelength such as ultraviolet rays and x-rays.These radiations alsoeffect the enzyme activity.pH:  Each enzyme has optimum pH.  Itsactivity slows down with increase in pH. Catalases and Amylose show optimumactivity in neutral solution. surcease and Ligase act in acidic medium.

Trypsinact in alkaline medium.     Reversibilityof enzyme: The popular of reaction catalyzedby enzymes are reversible. Thus an enzyme can speed up a reaction in bothdirections. Thus system state in equilibrium in a short time. In guard cell ofstomata the enzyme starch phosphorylase convert into starch and inorganicphosphate into glucose. The direction of reaction depend upon several factors.It depend upon pH and chemical potential of both reactions.

Synthesis of starchprotein and fats are irretrievable. 


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