Protein functions, nucleic acids and the amylase experiment
Lessons 27–29 · 3 lessons · A. Zikiryayev, A. To‘xtayev, I. Azimov, N. Sonin. Biology. Basics of Cytology and Genetics, Grade 9, revised and expanded 5th edition. “Yangiyul Poligraph Service”, Tashkent, 2019
29
Laboratory work 4: the action of amylase on starch
Textbook: p. 76
GoalObserve the action of the enzyme amylase on starch in an experiment and draw conclusions.
New words
amylase · amilazastarch · kraxmalreaction with iodine · yod bilan reaksiyacontrol tube · nazorat probirkasi
Explanation
Amylase breaks starch down to sugars; it is abundant in germinating grains and in saliva. Do the work under the teacher’s guidance: as the enzyme source use only your own saliva (hold a mouthful of water in the mouth for a few minutes and collect it in a clean beaker), while the iodine solution (about 1 %) and starch solution (about 0.5 %) are prepared by the teacher. In the first (control) tube, if you add water to starch and put in one drop of iodine, a dark blue-violet colour forms: starch is present. In the second tube, if you add saliva to starch, wait 5 minutes and add iodine, the colour is weak, reddish or yellow: the starch has been broken down. The iodine solution must not touch the mouth, eyes or skin; wash your hands after work and do not drink the solutions.
Worked examples
Control tube: starch + water + iodine → blue-violet (starch present). Test tube: starch + saliva + iodine → yellowish (no starch).
Result note: “Amylase broke the starch down; the blue colour with iodine disappeared. Conclusion: the enzyme is specific and acts on starch.”
Class activity
“Experiment plan”. Groups plan three variants (cold water, room temperature and warm — not boiling — water): how can the effect of temperature on enzyme speed be tested? Carry it out under the teacher’s supervision.
Practice
1
How does iodine show that starch is present?
A dark blue-violet colour appears where starch is present.
2
Why is a control tube needed?
For comparison: it shows that without the enzyme the starch remains, proving the colour change is due to the enzyme.
3
What would you expect in the experiment if the saliva were first boiled and cooled? Explain.
Iodine would again give blue: amylase is a protein and is denatured by boiling, so it does not work.
4
Why does bread taste sweeter the longer you chew it?
Salivary amylase breaks starch down into sugars (maltose).