Maharashtra BoardEnglish MediumSTD 11 ScienceBiologyBiomolecules5 Marks
Question
Enlist the factors affecting the activity of enzymes.
✓
Answer
The factors affecting the enzyme activity are as follows:
$1.$ Concentration of substrate:
$a.$ Increase in the substrate concentration gradually increases the velocity of enzyme activity within the limited range of substrate levels.
$b.$ A rectangular hyperbola is obtained when velocity is plotted against the substrate concentration.
$c.$ Three distinct phases $(A, B$ and $C)$ of the reaction are observed in the graph.
Where $V =$ Measured velocity, $V_{max} =$ Maximum velocity, $S =$ Substrate concentration,
$K_m =$ Michaelis$-$Menten constant.
$d. \ K_m$ or the Michaelis$-$Menten constant is defined as the substrate concentration $($expressed in moles/lit$)$ to produce half of maximum velocity in an enzyme catalyzed reaction.
$e.$ It indicates that half of the enzyme molecules $(i.e. 50\%)$ are bound with the substrate molecules when the substrate concentration equals the $\ Km$ value.
$f. \ K_m$ value is a constant and a characteristic feature of a given enzyme.
$g.$ It is a representative for measuring the strength of $ES$ complex.
$h.$ A low $K_m$ value indicates a strong affinity between enzyme and substrate, whereas a high $\ Km$ value reflects a weak affinity between them.
$i.$ For majority of enzymes, the $K_m$ values are in the range of $10_{-5}$ to $10_{-2} \ moles.$
$2.$ Enzyme Concentration:
$a.$ The rate of an enzymatic reaction is directly proportional to the concentration of the substrate.
$b.$ The rate of reaction is also directly proportional to the square root of the concentration of enzymes.
$c.$ It means that the rate of reaction also increases with the increasing concentration of enzyme and the rate of reaction can also decrease by decreasing the concentration of enzyme.
$3.$ Temperature:
$a.$ The temperature at which the enzymes show maximum activity is called Optimum temperature.
$b.$ The rate of chemical reaction is increased by a rise in temperature but this is true only over a limited range of temperature.
$c.$ Enzymes rapidly denature at temperature above $40^\circ C.$
$d.$ The activity of enzymes is reduced at low temperature.
$e.$ The enzymatic reaction occurs best at or around $37^\circ C$ which is the average normal body temperature in homeotherms.
$4.$ Effect of $pH:$
$a.$ The $pH$ at which an enzyme catalyzes the reaction at the maximum rate is known as optimum $pH.$
$b.$ The enzyme cannot perform its function beyond the range of its $pH$ value.
$5.$ Other substances:
$a.$ The enzyme action is also increased or decreased in the presence of some other substances such as co$-$enzymes, activators and inhibitors.
$b.$ Most of the enzymes are combination of a co$-$enzyme and an apo$-$enzyme.
$c.$ Activators are the inorganic substances which increase the enzyme activity.
$d.$ Inhibitor is the substance which reduces the enzyme activity.
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