Reactions to protein

How to determine the protein in front of us or not? You need to conduct quality reactions to protein, you will say, and you will be right. There are several such reactions. For biuret reactions, we need solutions of washing soda and copper sulfate.

You need to conduct quality reactions to protein, you will say, and you will be right

We prepare several solutions that contain protein, for example, meat and fish broth. Solution pour in test tubes about half. Add a little washing soda (a solution of soda is desirable to boil and cool). Then add a blue solution of copper sulfate. If in the test broth really there is a protein, then the color will immediately turn purple. Such characteristic reactions to the protein go only if there is indeed a protein in the solution.

Some of the protein molecules include, in addition to carbon, hydrogen, oxygen and nitrogen, also sulfur. We will carry out the following reaction to the protein. Put a little egg white in a tube with a solution of washing soda and, after heating the tube, add to it a little solution of the basic lead acetate Pb (CH3COO)2*3H2O. If the contents of the test tube turn black, then sulfur is: it forms lead sulfide PbS, a substance of black color.

Reactions to the protein can be carried out using its denaturation - coagulation with heating and transition into an insoluble form. Why, in order to prepare a delicious broth, you must put chopped meat in cold water, and when you want to cook tasty boiled meat, then large pieces are lowered into boiling water.

Pour cold water into a test tube, dip a little raw minced meat into it and heat. Gray flakes are formed in large quantities as they are heated. It is a curled protein, a foam that, when heated up further, passes from the meat into the solution and gives the broth a distinctive taste. And the meat becomes less tasty. If you boil water in advance in the test tube, and put the raw meat in boiling water, it will immediately turn gray, but the flakes are formed a little. The protein that was on the surface, under the influence of high temperature immediately curled and clogged numerous pores that permeate the meat. Moreover, proteins, including, can no longer go to solution. Hence, they remain inside the meat, giving it a good taste, and the broth, of course, gets a little worse.

It turns out that protein denaturation occurs not only when heated. Pour into a test tube of slightly fresh milk and drip one or two drops of vinegar or a solution of citric acid. Milk immediately sour, forming white flakes. It coagulates milk protein. By the way, without such a reaction to protein, do not cook cottage cheese.

When the milk is left in a warm place, then its protein is also curdled, but for a different reason - it's lactobacillus bacteria. They are known very much, and they all produce lactic acid, even if they do not eat milk. The reaction to the protein in this case can be done as follows. Filter a little sour milk and add a few drops of some homemade indicator to the serum. The color of the indicator will show that there is lactic acid in the solution.

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