ENZYMES

Defined as biological catalyst which speeds up the chemical reaction without being changed



Properties of proteins:
- globular
- tertiary structure
- water soluble
- specific active sites (depression in molecules)
- substrate specific
- temperature sensitive
- pH sensitive



Mechanism of action~
      speed of chemical Rx increases with an enzyme as it lowers the Ea


According to lock and key hypothesis:
- enzyme acts as a lock while substrate fits into it as a key


Induced fit hypothesis:
- according to this the tertiary structure of the protein forms active site which needs to change or shift a little bit as the substrate comes to it and finally binds with the enzyme forming the enzyme substrate complex


Explanation of mechanism:
(enzyme molecule stays unchanged)
- in a mixture of enzyme and substrate the molecule are in a constant motion due to kinetic energy, this causes collision among the enzyme and substrate molecules to form enzyme- substrate complexes. substrate molecule then changes into product and since it changed the shape and structure, it leaves the active site



The rate of enzymatic reaction~
*as enzymes are needed in a minute quantity for a large quantity of substrate  (as the enzyme remain unchanged) the rate of reaction is very quick

*it is the first 30 second which are needed to estimate the rate of reaction of enzyme, this is called initial rate of reaction.

*the rate of reaction can be calculated by noting the rate of product formation in first 30 second or by the rate of disappearance of the substrate for first 30 seconds



Enzyme catalysed reaction is regulated as: 
1- a change in enzyme concentration
2- a change in substrate concentration
3- inhibition by the final product of the reaction


Effect of enzyme in enzyme catalysed reaction: decreases the activation energy and has no effect on the energy yield




Factors affecting rate of reaction~


1) Temperature:
- increase in temperature increases the rate of reaction to 1 limit (means optimum temperature)
- in which every 10°C rise in temperature. the rate of reaction increases x2
- the temperature at which an enzyme acts best is called optimum temperature e.g, enzymes of human body have optimum temperature of 37.5°C
- a further increase in temperature decreases enzyme activity till it is completely lost



Explanation:
*increase in temperature, increases kinetic energy which results in more collision between enzyme and substrate molecules, thus a high rate of enzyme substrate complexes. after optimum temperature the tertiary structure of enzyme is lost and active site are disturbed due to breakage of hydrogen and hydrophobic interaction
*the substrate can no longer fit in with the active site through hydrogen bonds since enzyme is denatured



2) pH:
- every enzyme has an optimum pH at which it works the best. a shift in the pH shows down the activity of the enzyme and finally makes it denatured, hydrogen and ionic bonds are distorted. this results in loss of active sites and enzyme substrate complexes can no longer be formed


                        Rx= 1/t
Concentration (enzyme)
with a constant concentration of substrate, the concentration of enzyme, if increase will result in the increase rate of reaction without any limiting factor 








Concentration (substrate)
with a constant concentration of enzyme an increase in the substrate concentration will increase in rate of reaction up to a limit after which the rate of reaction becomes constant because the active sites aren't available and become a limiting factor and the substrate molecule to wait for their availability









Enzyme Inhibitors~
a molecule which interrupts in the formation of enzyme substrate complex. thus inhibiting the enzyme activity is called an enzyme inhibitor. there are 2 types of inhibitors:



1) Competitive:
- has a structure to the substrate 
- it competes for as of enzyme with substrate 
- a competitive inhibitor bonds with enzyme at active site 
- increase substrate concentration can decrease the effect of inhibition 


2) Non- competitive:
- 3-D structure is different to the structure
- it doesn't compete for active site with substrate 
- binds with the enzyme else where and distorts active site
- no effect increases the effect of substrate concentration 






End product inhibition:
in a sequence of course of many reactions aided by enzymes, sometimes the end product becomes inhibitor of the enzymes and result in limited quantity of end product