Properties catalysts, called enzymes. Enzymes increase speed of

 

                                     Properties of Enzyme

Proteins that function as living catalysts,
called enzymes. Enzymes increase speed of metabolic reactions. Low contamination,
low temperature and increased breakdown are only possible with enzymes. Breakdown
is increased, with the product made to a great gradation of purity.

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General Characters:

Enzymes have following general characters:

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 significant for
proper function of enzymes.    

• Composed of C, H, O and N.
Sulphur may also be present.     

• One or more polypeptide chains
– large number of associated amino acids.

• Formed on the ribosomes –
translation of mRNA during protein synthesis.

• Demolished by high temperature
and unfavorable pH.

Catalytic Characters:

  Enzymes speed up the chemical reactions. They
are not spent in chemical reaction. An enzyme cannot start the reaction it can
only increase the speed of a reaction. The competence 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 closed into a
specific three-dimensional nature.

• The correct coiled
shape is important for enzyme action ‘tertiary structure’.  

• The shape gives the
enzyme special areas known as active sites.

• The well-matched
substrate molecules bind to the counterpart 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.

• Control the thousands
of different metabolic reactions in a cell and in the organism.

 • The activity of a cell is resolute by which
enzymes are active in the cell at that time.

 • Cell activity is altered by removing
specific enzymes and/or manufacturing new enzymes.

 Active
Site Theory :

“Lock and Key and
Induced Fit modal”

• The enzyme’s active
site has a shape opposite 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 weak
salt solution.They are insoluble in non-polar solvent like eather.

 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.They act as buffer in acid and base solution.

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 excesses
of temperature, high salt, organic solvents e.g, 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 organization 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) Groups of enzymes:

(b) Groups of substrate:

During enzyme action,
there is a temporary combination between enzyme and its substrate forming
enzyme by relatively weak forces. This occurs at the active site of the enzyme
(most substrates are bound to the enzyme by relatively weak forces.In this
enzyme substrate complex formed .

                  E + S          à           ES complex

 

  Activation energy:

 Is minimum energy that is
required to start a reaction called activation energy. Enzymes lower the
activation energy. The reaction can take place in the absence of enzyme. But it
need higher amount of activation energy.Lower the activation energy also
destroyed the enzyme setrecture.

 

 

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.It also destroyed
the cell setrecture.

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 at 0 Degree.to -10 Degree.At low tempreture enzymes
do not work.

e)      Radiation: 

f)       Enzymes are also destroyed by radiation of
lower wavelength such as ultraviolet rays and x-rays.These radiations also
effect the enzyme activity.

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 popular 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 irretrievable.