Page 35 - exemple

Exercises

a- In reference to the text:
1) Indicate the constituent molecules of wheat starch.
2) Define « hydrolysis ».
3) Pick out the sentence that shows the role of enzymes.
b- Name the enzyme responsible for the molecular simplification of wheat starch.
c- Schematize the molecular simplification of starch (cooked starch) in the presence of saliva.
Lebanese brevet 2009

16 Effect of the temperature on the enzymatic activity

To determine the effect of temperature on the enzymatic activity, we place five test tubes
containing the same quantity of cooked starch and the same enzyme: salivary amylase, at different
temperatures. Fifteen minutes later, we measure the activity of this enzyme in each of these test

tubes. The measured results are shown in the table below.

Table showing the variation of the enzymatic activity
as a function of the temperature

Temperature (in °C) 0 20 37 45 60
Enzymatic activity (in %) 0 20 100 15 0

a- Draw a graph showing the variation of the enzymatic activity in function of temperature.
b- Analyze the obtained results, above table.
Draw out a conclusion concerning the property of the enzyme.
c- The test tube that was placed at 60°C, is placed at 37°C.
Will the enzymatic activity, in this case, be changed? Justify the answer.
Lebanese brevet 2009

17 The «in vitro» digestion of milk lipids

In studying the « in vitro » digestion of milk lipids (cream), we realize the following experiment.
Four test tubes are placed in a water bath, at 37ºC.
They contain water, cream, and red phenol (indicator).
We add bile in tubes 2 and 4, and lipase in tube 3 and 4.
a- Schematize the described experiment. After 3 hours, we observe the color in the tubes: the
content of tubes 1 and 3 is red, tube 2 is pink and tube 4 is yellow.
b- Analyze the result of the experiment.
What can you deduce concerning the action of the pancreatic lipase?
c- Construct a table showing the color of the content of the tubes after 3 hours.
d- Formulate a hypothesis explaining the role of the bile.
e- Compare the results in tubes 3 and 4 at the end of the experiment. Does this validate the
hypothesis? Justify the answer.
f- Schematize the transformation of lipids.
N.B.: The red phenol is an indicator that shows a pink color in an alkaline medium and yellow
color in a acid medium.

Digestion 39