Theoretical Basis Proteins

THEORETICAL BASIS PROTEINS Protein comes from the Latin word proteios which means first or something most important thing in life. Protein is an organic compound that is part of protoplasm, cell walls and organelles of plant and animal cells. This compound composes about 20% of the dry weight of animal and human cells. The nature, shape and characteristics of proteins as a group of biological compounds determined by its chemical composition. Composition and sequence of amino acids, as the basic unit that makes up a protein, determines the spatial shape (conformation) of the protein. The shape of this space is very important in protein activity and function. Difference composition, spatial shape, and properties of proteins found in different tissues, both from different animal and plant species. This difference is basically related to the specificity of the animal tissue and species, which closely related to certain proteins found in protoplasm and organelles the animal or plant tissue cells in question. In general, elemental composition Protein consists of 50% carbon (C), 7% hydrogen (H), 16% nitrogen (N), 0-3% sulfur (S), and 0-3% phosphorus (P). The presence of the element nitrogen (N) is a characteristic of the molecule proteins. Protein is the most important nutrient with many functions various, starting from being a source of energy such as carbohydrates and fat, enzyme catalyst, cell structure element, transport tool, protector, regulator, element contractile, and so on. The following are several tests that can show the presence of protein, which based on the arrangement of elements, colloidal properties of the solution, color reactions and precipitation protein molecules. HOW IT WORKS ELEMENTARY COMPOSITION TEST Ways of working: A.1. Put a small and dry, 2. The smell contains 3. The black amount of albumin flour into a clean test tube heat slowly. of burning hair is characteristic of this compound nitrogen like protein. color that appears indicates the presence of carbon. 4. Condensation at the top of the tube indicates the presence of oxygen and hydrogen. B. 1. Put a little albumin flour into the tube, add the crystals NaOH is twice the volume of albumin. Heat carefully. 2. Note the smell of ammonia and the effect of its vapors on the litmus paper red that has been moistened with water. 3. It indicates the presence of nitrogen and hydrogen. BIURET TEST The biuret test is a good general test for protein. Alkaline copper sulfate reacts with compounds containing many peptide bonds (such as proteins) forms a purple complex. This complex nature is not what it really is is known. The intensity of the color obtained indicates the number of peptide bonds in the proteins. The name of this test comes from the characteristic biuret compound. No reaction really specific for proteins because every compound has two carbonyl groups which is bound by nitrogen or carbon (amide acid groups (-CONH2, -CSNH2 and CRHNH2) will produce a positive reaction. Ways of working a. 1. Provide 3 tubes and fill them 2. Stir well, if there is no pink or purple color Addd another drop of CuSO4. Continue this addition (maximum up to 10 drops) until a pink or purple color forms. b. 1. Put 2 ml of 2% albumin solution into the tube, add 2 ml 40% NaOH solution, stir well. 2. Carefully tilt the tube, pour 5 ml of CuSO4 solution 0.02% through the tube wall to form two layers of color clear. 3. Leave it for a few minutes and observe the color that occurs when it meets both solutions. c. This test is not specific to proteins because other compounds are present as well gave the same reaction to biuret reagent. 1. Put a small amount of urea into a test tube and heat it above small flame so that the urea melts and boils. Be careful not to make up. 2. Pay attention to the smell of gas coming out. 3. Dissolve the contents of the tube with water, do a biuret test (add CuSO4 and NaOH). 4. Write the reaction for the formation of biuret from urea. NINHYDRINE TEST Ninhydrin (triketohydrindene hydrate) is a strong oxidizing compound which reacts with all alpha amino acids and at pH 4-8 produces color purple. All amino acids, except proline and hydroxy proline, react with ninhydrin forms its lower aldehyde derivative (which is colored blue) by releasing CO3 and NH3. The imino acid proline and hydroxy proline as well reacts with ninhydrin, but produces a yellow color. Ammonium compounds strong and primary amines show the same reaction but do not liberate CO2. Ways of working 1. Provide 4 test tubes and fill them 2. Place the tube in a boiling water bath for 10 minutes. 3. Pay attention to the color changes that form. The blue color indicates its presence Amino compounds other than proline and hydroxyproline. REACTION WITH HEAVY SALT At pH 7 or above, proteins are usually negatively charged. Metal ions positively charged will neutralize the charge of this protein so that the protein will settles. Therefore, reactions with heavy metals are most effective at neutral pH or slightly alkaline, although the solution does not need to be too alkaline as it will cause metal hydroxy deposition occurs. The precipitate formed often dissolves in Excessive heavy metal solutions because excess metal provides charge stability positive on precipitate particles. Ways of working: 1. Provide 5 test tubes and fill them 2. After each addition of 1 drop of salt, shake carefully and pay attention to the impact it has. 3. Pay attention to the precipitate that forms, whether it remains or dissolves again or increase in size after each addition of salt and with excess salt in question. 4. If the salt is poisonous, which salt is albumin? can be used as an excellent antidote, why? REACTION WITH WEAK SALT Ways of working: 1. Provide 5 test tubes and fill them 2. After each addition of 1 drop of salt, shake carefully and Pay attention to the impact it has. 3. Pay attention to the precipitate that forms, whether it remains or dissolves again or increase in size after each addition of salt and with excess salt in question. 4. Compare the results of this reaction with experiment 4.