Suppose a certain biologically important reaction is quite slow at physiological temperature (37 °C) in the absence of a catalyst. Assuming that the frequency factor remains the same, by how much must an enzyme lower the activation energy of the reaction to achieve a million- fold (1.0 x 106) increase in the reaction rate constant?

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Answer:

The answer to the question is

The enzyme must lower the activation energy by 35624.5 KJ/mol

Explanation:

The relation is

k = [tex]Ae^{\frac{-Ea}{RT} }[/tex]

Where k = rate of chemical reaction

A = Arrhenius constant

Ea = Activation energy

T = Temperature

R = Gas constant

at 37 °C we have T = (37 +273.15)  K = 310.15 K

k = [tex]Ae^{\frac{-Ea}{(8.314)(310.15)} }[/tex]

when a catalyst is introduced we have Ea(catalyst)

kc = [tex]Ae^{\frac{-Eacatalyst}{(8.314)(310.15)} }[/tex]

Finding the ratio of the two reaction rate and noting that Kc/K = 1.0 x 10⁶

Thus we have

Kc/k = [tex]\frac{Ae^{\frac{-Eacatalyst}{(8.314)(310.15)} }}{Ae^{\frac{-Ea}{(8.314)(310.15)} }}[/tex]  = 1.0 x 10⁶ by taking natural logarithm of both sides, we have

6 × ln (10) = Ln (Kc/k ) = [tex]{\frac{Ea}{(8.314)(310.15)} }- {\frac{Eacatalyst}{(8.314)(310.15)} }[/tex]  

so that Ea - Eacatalyst = 8.314 × 310.15 × 13.816 = 35624.5 KJ/mol

Therefore the enzyme must lower the activation energy by 35624.5 KJ/molto achieve a million fold increse in the reaction rate constant

The enzyme must lower the activation energy by 35624.5 KJ/mol

The relation for activation energy and rate constant:

[tex]k = Ae^\frac{-E_a}{RT}[/tex]............(1)

where

k = rate of chemical reaction

A = Arrhenius constant

Ea = Activation energy

T = Temperature

R = Gas constant

Given:

Temperature= 37 °C we have T = (37 +273.15)  

In Kelvins, T = 310.15 K

On substituting the values in equation (1)

[tex]k = Ae^\frac{-E_a}{RT}\\\\[/tex]

The ratio's for the two reaction rate will be:

[tex]\frac{k_c}{k}=\frac{Ae\frac{-E_{c}}{RT} } {Ae\frac{-E_a}{RT} }=1.0*10^6[/tex]

Taking log both sides:

[tex]6*ln (10)=ln\frac{k_c}{k} =\frac{E_a}{RT} =\frac{E_c}{RT}[/tex]

On further solving,

[tex]E_a-E_c=8.314*310.15*13.816=35624.5KJ/mol[/tex]

Thus, the enzyme must lower the activation energy by 35624.5 KJ/mol to achieve a million fold increase in the reaction rate constant.

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