Properties of Enzyme: Proteins that work as biological catalysts, called enzymes. Enzymes increase speed of metabolic reactions. Low contamination, low temperature and increased metabolism are only possible with enzymes. Metabolism is increased, with the product made to a high degree of purity. General Properties: Enzymes have following general properties: Protein Nature of Enzymes: Most of enzymes are globular proteins.
some enzymes like ribozymes are nucleic acid in nature. Globular structure of proteins is very important for proper works of enzymes. • Composed of C, H, O and N. Sulphur may also be present. • One or more polypeptide chains – large number of linked amino acids. • Formed on the ribosomes – translation of mRNA during protein synthesis. • Destroyed by high temperature and unfavorable pH.
Catalytic Properties: Enzymes speed up the chemical reactions. They are not consumed in chemical reaction. An enzyme cannot start the reaction it can only increase the speed of a reaction. The efficiency of an enzyme reaction is expressed form of turner number. The number for sucrose’s is 105 and for catalases is 106.
Folded Shape of Enzymes :• The polypeptide chains are folded into a specific three-dimensional shape. • The correct folded shape is important for enzyme action ‘tertiary structure’. • The shape gives the enzyme special areas known as active sites. • The compatible substrate molecules bind to the complement active site. • Different enzymes have a differently shaped active site.• Higher temperatures more kinetic energy, so more collisions Role of Enzymes in Living Things: Enzymes catalyze all metabolic reactions.
• They lower the activation energy – the energy input needed to bring about the reaction. • Regulate the thousands of different metabolic reactions in a cell and in the organism. • The activity of a cell is determined by which enzymes are active in the cell at that time. • Cell activity is altered by removing specific enzymes and/or synthesizing new enzymes. Active Site Theory :”Lock and Key Hypothesis and Induced Fit” • The enzyme’s active site has a shape complementary to the substrate.
• The substrate locks into the active site of the enzyme. • The active site alters its shape holding the substrate more tightly and straining it. • An enzyme-substrate complex is formed. • The substrate undergoes a chemical change – a new substance is formed. • The product is released from the active site. • The free unaltered active site is ready to receive fresh substrate. Solubility: Enzymes as proteins are soluble in water or dilute salt solution Molecular weight :Enzymes have high Mw (varying from 10000 -several thousands)Enzymes have buffering capacity: They are amphoteric molecules i.e.
behave both as acids and bases. At pKa they make the most efficient buffer.Each enzyme has a specific isoelectric pH: It is the pH at which the net charge on protein equal to zero –so they do not move in an electric field. It is the pH at which the protein molecule carries equal positive and negative charges Above PI -negatively charged can move in an electric field Below PI -positive charged and can move under an electric field.Denaturation: When proteins are heated , or subjected to extremes of temperature, high salt, organic solvents etc, the non-covalent bonds break, changing the native structure to random coil.
This unfolding of protein is due to loss of secondary, tertiary and quaternary structure. It does not affect primary 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 containing phenylalanine end tyrosine—give orange color.(ii)Mallon’s reaction: Proteins containing phenolic(-OH) group of tyrosine—give red color(iii) Sulfate reaction: Proteins containing sulfur amino acids (cysteine) —-give black or grey color(iv)Biuret’s Test:•This is a general test for all proteins because it O is given by peptide linkage ( C -N) H•The reaction occurs between protein, sodium hydroxide and copper sulfate giving violet complex.Specificity: The specific of enzyme is due to primary amino acids sequence.
e.g. sucrose acts upon sucrose and lactase on milk sugar.•Enzymes are highly specific. They are specific for: •the reactions they catalyze. •and in their course of reaction, which are called substrates. (a)Absolute specificity: The enzyme can act only on one specific substrate.
(b)Group specificity:•Broad specificity •Enzyme act on a group of related substrates. •The substrates have a common group on which the enzyme acts: e.g. -esterase can act on different esters -proteases can act on different protein e.g. of proteases: chymotrypsin, trypsin, pepsin.The specificity is due to substrate binding site which lies on the enzyme surface -in specification is due to the specific arrangement of amino acids in the active site that participate in the bond making and bond breaking. The specification of an enzyme is determined by:(a)Workal groups of enzymes(b)Workal groups of substrate During enzyme action, there is a temporary combination between enzyme and its substrate forming enzyme by relatively weak forces.
This occur at the active site of the enzyme (most substrates are bound to the enzyme by relatively weak forces. E + S ? ES complex Activation energy: is minimum energy that is required to start a reaction. Enzymes lower the activation energy. The reaction can take place in the absence of enzyme. But it need higher amount of activation energy. Product Inhibition: The accumulation of products of the reaction can inhibit the enzyme activity. The effect is very important for cell. It maintain the concentration of the product in a cell.
Allosterism: Some enzymes have specific allosteric site for binding of certain effecters. The binding of effecters change in the structure of enzyme. Allosteric is shown by many enzymes.
Sensitivity of Enzyme: Enzymes are sensitive for following factors:a) High Temperature: b) Enzymes are sensitive for heat. Activity of enzymes increase with the increase of temperature of to 50 degree. The enzymes are denatured at 70 to 100 degree. Such conditions are present in spore and dry seeds. c) b) Low Temperature: d) Enzymes are also sensitive for low temperature. They are inactivated but not destroyed at 0 degree. e) Radiation: f) Enzymes are also destroyed by radiation of lower wavelength such as ultraviolet rays and x-rays.pH: Each enzyme has optimum pH.
Its activity slows down with increase in pH. Catalases and Amylose show optimum activity in neutral solution. surcease and Ligase act in acidic medium. Trypsin act in alkaline medium. Reversibility of enzyme: The majority of reaction catalyzed by enzymes are reversible. Thus an enzyme can speed up a reaction in both directions. Thus system state in equilibrium in a short time.
In guard cell of stomata the enzyme starch phosphorylase convert into starch and inorganic phosphate into glucose. The direction of reaction depend upon several factors. It depend upon pH and chemical potential of both reactions. Synthesis of starch protein and fats are irreversible.