BIOCHEMISTRY SLIDES

2. ENZYMES
 DEFINITION
 Enzymes are proteins that function as biological
catalysts. A catalyst is a substance that speeds up a
chemical reaction but isn’t changed by the reaction.
 Enzymes catalyze all aspects of cell metabolism.

3.  Enzymes are highly specific to the
reactions they catalyze
 They alter or speed up the rates of
chemical reactions that occur in a
cell.
 They remain unchanged after a
chemical reaction.
 They are affected by temperature.
 They are affected by pH.
 They catalyze reversible reactions.
PROPERTIES OF
ENZYMES

4. DISTRIBUTION
 Enzymes are not randomly distributed but are
specifically located inside the cells for example
 Digestive Enzymes: (Pancreas and stomach)
 Glycosol :( oxidation of glucose)
 Mitochondria TCA cycle

5. GROUPS OF ENZYMES
THERE ARE SIX MAJOR GROUPS OF ENZYMES

6. ENZYME PORTIONS
Enzymes are composed of:
1.APO ENZYME : Protein portion
consisting of amino acid chains
2. CO- FACTORS activate
enzymes and are not protein
parts.
 HOLOENZYME (conjugated
enzyme)
 Both cofactors and apo enzymes
help to form a conjugated
enzyme called holoenzyme.

7. 3. SUBSTRATE AND ACTIVE
SITE :
 Enzymes operate by binding to
a substrate
 The catalytic (active) site is the
portion of the enzyme where
substrate binding occurs.

8. MECHANISM OF ENZYME ACTION
1 .THE LOCK-AND-KEY HYPOTHESIS
 It was suggested by
Arrhenius that the shape of
the Active Sites of Enzymes
is exactly Complementary to
the shape of the Substrate.

9. 2.INDUCED FIT MODEL
 A more recent model
suggested by Daniel
Koshland the Induced-
Fit Model.
 It states that the shape
of Active Sites are not
exactly Complementary,
but are changed
according to the
substrate molecules

10. FACTORS AFFECTING THE RATE OF
ENZYME ACTIONS
 1. TEMPERATURE
 Enzymes have an optimum
temperature at which they work
fastest.
 Up to the optimum temperature
the rate increases
 Above the optimum temperature
the rate decreases

11.  2. pH
 Enzymes have an optimum pH at which they work
fastest.
 For most enzymes this is about pH 7-8
 but a few enzymes can work at extreme pH, such as
protease enzymes in animal stomachs, which have an
optimum of pH 1.

12. 3. ENZYME CONCENTRATION
 As the enzyme concentration increases the rate of the
reaction increases linearly
 At very high enzyme concentration the substrate
concentration may become rate-limiting

13. 4. SUBSTRATE CONCENTRATION
 As the substrate concentration increases, the rate
increases because more substrate molecules can
collide with enzyme molecules, so more reactions will
take place

14. INHIBITION CAN BE EITHER COMPETITIVE OR
NONCOMPETITIVE
1. COMPETITIVE INHIBITION: Competitive
inhibition is the interruption of an enzyme's ability to
bind to a substrate due to a different molecule binding
to the active site.

15. 2. NON COMPETITIVE INHIBITION :
 Non competitive inhibitors are not similar to the
substrate and they do not bind to the active site of the
enzyme.
 They change the conformation of the active site.

16. ROLE OF ENZYMES IN THE BODY
1. DEGRADATION REACTIONS
(CATABOLIC)
2. SYNTHESIS (ANABOLIC)
3. DIGESTION Enzymes are used
for a wide variety of
purposes, such as in digestion.
4.PROTECTION
Enzymes are also used in protection
against Pathogens. They can be
used to destroy invading
Microorganisms.