Experiments with enzymes: amylases. Fun chemistry experiments at home

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Experiments with enzymes: amylases. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

Enzymes speed up many chemical reactions, but they do so selectively. Each of them has its own narrow "specialty", the same process is sometimes accelerated by several enzymes. This is what we will now verify.

Let us consider the enzymes that destroy starch with the addition of water molecules to its "fragments", i.e. hydrolytic enzymes. Among them are amylases, which we have already talked about in the chapter "Experiments with carbohydrates". Since you already know the essence of the action of such enzymes, we will immediately engage in comparative experiments: we will check how human and animal amylases act on starch.

The source of human amylase, as before, will be saliva. Amylases of animal origin can be found in bee honey.

Prepare five solutions first. First solution: collect about 0,5 ml of saliva in a test tube and dilute twenty times with cold boiled water. Second solution: very liquid starch paste (a quarter of a teaspoon of starch in a glass of water). The third solution: pharmacy iodine tincture diluted with water twenty times. Fourth solution: two or three drops of bee honey diluted ten times with water and thoroughly mixed. Fifth solution: half a teaspoon of baking soda to ten tablespoons of water.

This time you will need nine test tubes. Pour about 5 ml of paste into all test tubes. In tubes 1, 4 and 7, add 5 drops of vinegar with a pipette, and in tubes 2, 5 and 8, add the same amount of soda solution. Add 5 drops of pure water to the remaining tubes. Mix the contents of all test tubes and add 10 drops of diluted saliva to each.

After 10 minutes, add one or two drops of iodine solution to test tubes 1, 2 and 3 and mix the mixture. Watch for color change. After another 15 minutes, add the same portion of iodine to tubes 4, 5, and 6, and after another 10 minutes, add to the remaining tubes. Starch and dextrins, as you remember, give a different color with hearth, and as the amylase breaks down the starch, the color changes. So you can judge not only the breakdown of starch, but also which environment - acidic, neutral or alkaline - is more favorable for this process.

The experiment with bee honey is set up in exactly the same way. The activity of amylases in different samples can fluctuate greatly, therefore, the hydrolysis time may have to be reduced or increased. For example, the saliva of heavy smokers contains very little amylase.

For the next experiment, you will need barley malt - germinated barley grains. Dip the grains in water for a few hours and let them germinate on a saucer for 4-5 days, adding a little water every day. Separate the sprouts, rinse with water and rub thoroughly with a wooden pestle or spoon. Dilute the gruel with a double amount of distilled water and squeeze it through a dense cloth into a glass. This extract contains two enzymes: alpha-amylase and beta-amylase. With additional processing, one of them can be destroyed in order to observe the action of the other. Alpha-amylase is destroyed by heating. Add three parts of water to one part of the barley extract, stir the mixture and heat it for 20 minutes in a water bath at 70 0C, stirring thoroughly. The cooled solution contains beta-amylase.

Now, to get a solution of alpha-amylase, you need to destroy the beta-amylase with acid. Cool about 5 ml of the extract to 2-3 ° C in the refrigerator or on ice, add an incomplete teaspoon of chilled vinegar and add cold water to the test tube almost to the top. Mix the mixture and leave for 15-20 minutes, and then neutralize the solution by adding chalk powder until the bubbles stop. Stir the mixture again, dilute twice with water, let stand and drain the liquid over the precipitate into a clean test tube. This completes the preparation for the experiment.

Pour into ten test tubes 1 ml of starch solution and 9 ml of water. Add ten drops of alpha-amylase solution with a pipette to test tubes 1-5, add the same amount of beta-amylase solution to the remaining test tubes, mix the contents of all test tubes. After 3 minutes, add one drop of iodine solution to test tubes 1 and 6 and stir. Do the same with test tubes 2 and 7 after 5 min, 3 and 8 after 10 min, 4 and 9 after 20 min, 5 and 10 after 30 min.

You will notice that in the presence of alpha-amylase, the color changes rapidly: blue-violet - pink-yellow: in this case, dextrins are formed - fragments of starch molecules. Beta-amylase acts differently: it seems to "bite off" pieces from starch molecules, and therefore the color with iodine remains blue, but as the starch decomposes, its brightness decreases.

The results of this experiment clearly show the diversity of properties even for similar enzymes. In living organisms, enzymes usually act together. The transformations that take place are much more complicated than those relatively simple reactions that you observed in test tubes. But the knowledge of the simple is the first step to the knowledge of the complex.

Author: Olgin O.M.

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