Page 18 - exemple

The enzyme is inactive at 0°C; its activity is regained at 37°C.
The enzymes are active at the normal temperature of the organism between 35°C and 40°C.
When the temperature is equal 0°C the enzyme is inactivated.
When the temperature is > 60°C the enzyme is denatured.

3 Specificity of enzymes Cooked Fresh Cooked
starch saliva Pepsin starch
Place in a water bath at 37°C two test tubes solution solution
(A) and (B) containing a solution of cooked
starch.
Add fresh saliva to tube (A) and pepsin to
tube (B). 37ºC 15
15 minutes later. minutes
A B later A B
Tube (A) turns brown orange when we add
iodine water to it. Doc 9- Experiment showing the specificity of
Tube (B) takes a dark blue coloration when enzymes.
we add iodine water to it.
Thus, each enzyme accelerates the hydrolysis of a specific substrate:
Salivary amylase acts on cooked starch but pepsin has no activity on it.
Sucrase acts on sucrose, maltase on maltose…

4 Catalytic role of enzymes

In a tube containing cooked starch without saliva, sugar molecules form few days later. Thus, the
enzyme accelerates considerably the reaction that can occur spontaneously without it, but with a
very slow pace.
- The enzyme is not destroyed during the reaction; it remains intact at the end of the experiment.
- The enzyme is active even in a very low concentration.

Probing of activity 2

1- Pick up the necessary information from documents 1 and 2.
2- Draw a table that represents the results of the iodine and the Fehling test applied on three
tubes A, B and C.
3- Is the digestion of starch by the salivary amylase modified by the pH conditions of the
medium? Justify your answer.
4- Analyze the results of document 7. Compare the optimal values for the gastric pepsin
enzymes and pancreatic enzymes. What can we conclude?
5- Design an experiment showing that a temperature > 60°C denatures the enzyme.
6- Pick up the optimal convenient temperature to the activity of enzymes.
7- Analyze the results of the experiment 9 and conclude the studied property of the digestive
enzymes.
8- Does pepsin act in a neutral medium? Justify your answer.

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