Biomolecules

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is the difference between average energy of substrate from that of

transition state.



If the product (P) is at a lower energy level than the substrate (S), the

reaction is an exothermic reaction (spontaneous reaction). It requires no

energy (by heating) to form the product.



In a biochemical reaction, enzymes lower the activation energy. As a

result, speed of the reaction increases.



Rate of reaction can be doubled or decreased by half for every 10°C

change in either direction.

FÅÇTØRS ÅFFËÇTÏÑG ËÑZÝMË ÅÇTÏVÏTÝ

Å) TËMPËRÅTÜRË ÅÑD PH



Enzymes show highest

activity

at

optimum

temperature

&

pH.

Activity declines below

and

above

optimum

value. (AIPMT 2010, 2011)



At

low

temperature,

enzyme temporarily becomes inactive.



At high temperature, enzymes destroy because proteins are denatured

by heat.



Inorganic catalysts work at high temperature & pressure. But enzymes

get damaged at high temperature (> 40°C).



Thermophilic organisms have enzymes which are stable at high

temperature (up to 80-90°C).

B) ÇØÑÇËÑTRÅTÏØÑ ØF SÜBSTRÅTË

With

the

increase

in

substrate

concentration, the velocity of enzyme

action rises at first and reaches

a maximum velocity (Vmax). This

is not exceeded by further rise in

concentration

because

enzyme

molecules

are

fewer

than

the

substrate molecules i.e. No free

enzyme molecules present to bind

with additional substrate molecules.

V max

Ve o

l c y

ti

of reac

n

o

it

V

( )

[S]

V

2

max

K m

(c)

Rate of Reaction

Temperature

Optimum Temp.

Rate of Reaction

Optimum pH

pH