starch+and+proteins

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 * Name and Surname: Class:**
 * Hand in the activity to your teacher the day after you go to the lab**

**BIOLOGICAL MOLECULES AND FOOD TESTS**


 * Material: **
 * Lugol || Eyedropper || Test tubes ||
 * Food: onions, rice, sugar, wheat, corn, potatoes || Microscope slide || Biuret agent: sodium hydroxide (NaOH) and Copper sulphate (SO4Cu2) ||
 * Tweezers || Petri dishes || Food: water, egg white, yolk, milk, potatoes, sugar ||


 * Objectives: **

Identify polysaccharides using Lugol's reagent with a colorimetric reaction (change of colour) Carbohydrates are divided as simple sugars, disaccharides or polysaccharides. **Monosaccharides** or simple sugars such as glucose and fructose (C6H12O6) function as energy source in cells during cellular respiration and are also used to build cell structures and other organic molecules within the cells. **Disaccharides** are composed of two monosaccharide joined together. Sucrose (table sugar) is a disaccharide composed of one glucose and one fructose molecule. **Polysaccharides**: Are long chains of monosaccharides bonded together. Plants store excess glucose in the form of starch, a polysaccharide composed of long chains of glucose. Pure starch is a white, tasteless and odourless powder that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear and [|helical][|amylase] and the branched [|amylopectin] Lugol's reagent changes from a brownish or yellowish color to **blue-black** when starch is present, but there is no color change in the presence of monosaccharides or disaccharides. Answer following question: **Objectives: **
 * Previous Knowledge **
 *  [|LUGOL'S TEST FOR STARCH] **
 * 1) Using the tweezers, take some samples of different foods to make the test
 * 2) Place them on a microscope slide
 * 3) Put a couple of drops of Lugol agent
 * 4) Complete the table with the results:
 * **FOOD** || **Positive (+) or negative (-) reaction** || **Starch (yes or no)** ||
 * Onion ||  ||   ||
 * Rice ||  ||   ||
 * Sugar ||  ||   ||
 * Wheat ||  ||   ||
 * Potatoes ||  ||   ||
 * Corn ||  ||   ||
 * 1) Does the sugar sample have starch? How do you know?

Testing proteins using Biuret agent with a colorimetric reaction. **Previous Knowledge ** Proteins are made up of one or more polypeptides which are linear polymers of smaller molecules called amino acids. Amino acids derive their name from the amino group and the carboxyl group (acidic) that each possesses. Polypeptides are formed when amino acids are joined together by peptide bonds between the amino group of one amino acid and the carboxyl group of a second amino acid. The tests for proteins will be done: The Biuret reagent reacts with peptide bonds and will, therefore, react with proteins, like egg albumin. Biuret solution is a blue liquid that changes **to purple** when proteins are present and to pink in the presence of short chains of polypeptides. The copper atom of the biuret solution reacts with the peptide bonds to cause the colour change. 1. Define the term "positive control." What is the pupose of a positive control? Give an example of a positive control in the Benedict's Test. 2. Specifically, what does the Biuret reagent detect? Why would this test NOT detect an amino acid? 3. Why was water used as a test solution in each of the tests? What was its function or role in the exercises?
 * BIURET TEST FOR PROTEINS **
 * 1) on water (to demonstrate negative results)
 * 2) on egg white which contain the molecules being tested for (to demonstrate positive results)
 * 3) on several substances of unknown composition
 * 1) Take some samples of different foods to make the test in test tubes
 * 2) Add a drop of Biuret agent
 * 3) Shake the mixture
 * 4) Write down your results on the following table
 * **FOOD** || **Positive (+) or negative (-) reaction** || **Starch (yes or no)** ||
 * water ||  ||   ||
 * Egg white ||  ||   ||
 * Sugar solution ||  ||   ||
 * Yolk ||  ||   ||
 * Milk ||  ||   ||
 * Potatoe ||  ||   ||
 * Summary Questions: **