Page 16 - exemple

C- Properties of enzymes

Importance of pH on the activity of enzymes

♦ Concept of pH

The classification of acidic solutions and basic
solutions is done according to their pH.
The pH or hydrogen potential is a number that varies
between 1 and 14. This number characterizes the
acidic, basic or neutral state of the solution.
A solution of :
pH = 7 signifies that the solution is neutral (neither
acidic nor basic) such as pure water.
pH < 7 signifies that the solution is acidic. As the
Doc 3- pH indicator.
pH gets closer to 1 the solution becomes
more acidic.
pH > 7 signifies that the solution is basic. As the pH gets closer to 14 the
solution becomes more basic.

♦ Identification of the importance of pH
Take three test tubes A, B and C containing:
3
Tube A: 10 cm of cooked starch + fresh saliva.
3
Tube B: 10 cm of cooked starch + fresh saliva + few drops of hydrochloric
acid.
3
Tube C : 10 cm of cooked starch + fresh saliva + few drops of caustic soda
(NaOH).
Let the reagents react.
Perform the iodine test and
Doc 4- The pH
Fehling test on samples
meter is used to
taken from from each test
determine the pH
tube. The dark blue
of a solution.
disappears in tube A only.
Enzyme pH

Salivary amylase 7

Pepsin 3,5

Sucrase 7,8

Lipase 7,8

Protease 7,8
Doc 5- The digestion of starch in the presence
of saliva depends on the pH of the
Doc 6- The pH of some enzymes.
medium.

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