Detection of Biological Molecules

Topics: Starch, Chemical tests, Glucose Pages: 6 (1566 words) Published: October 8, 1999
Detection of Biological Molecules

Introduction: Without carbon, nitrogen, hydrogen, sulfur, oxygen and phosphorus, life wouldn't exist. These are the most abundant elements in living organisms. These elements are held together by covalent bonds, ionic bonds, hydrogen bonds, and disulfide bonds. Covalent bonds are especially strong, thus, are present in monomers, the building blocks of life. These monomers combine to make polymers, which is a long chain of monomers strung together. Biological molecules can be distinguished by their functional groups. For example, an amino group is present in amino acids, and a carboxyl group can always be found in fatty acids. The groups can be separated into two more categories, the polar, hydrophilic, and the nonpolar, hydrophobic. A fatty acid is nonpolar, hence it doesn't mix with water. Molecules of a certain class have similar chemical properties because they have the same functional groups. A chemical test that is sensitive to these groups can be used to identify molecules that are in that class. This lab is broken down into four different sections, the Benedict's test for reducing sugars, the iodine test for the presence of starch, the Sudan III test for fatty acids, and the Biuret test for amino groups present in proteins. The last part of this lab takes an unknown substance and by the four tests, determine what the substance is.


Introduction: Monosaccharides and disaccharides can be detected because of their free aldehyde groups, thus, testing positive for the Benedict's test. Such sugars act as a reducing agent, and is called a reducing sugar. By mixing the sugar solution with the Benedict's solution and adding heat, an oxidation- reduction reaction will occur. The sugar will oxidize, gaining an oxygen, and the Benedict's reagent will reduce, losing

an oxygen. If the resulting solution
is red orange, it tests positive, a change to green indicates a smaller amount of reducing sugar, and if it remains blue, it tests negative.

Materials: onion juice5 test tubes1 beaker potato juice
rulerhot plate deionized waterpermanent
marker5 tongs glucose solutionlabels starch solution6 barrel pipettes Benedict's reagent5 toothpicks

Procedure: 1.Marked 5 test tubes at 1 cm and 3 cm from the bottom. Label test tubes #1-#5. 2.Used 5 different barrel pipettes, added onion juice up to the 1 cm mark of the first
test tube, potato juice to the 1 cm mark of the second, deionized water up to the 1
cm mark of the third, glucose solution to the 1 cm mark of the fourth, and the
starch solution to the 1 cm mark of the fifth test tube. 3.Used the last barrel pipette, added Benedict's Reagent to the 3 cm mark of all 5
test tubes and mix with a toothpick. 4.Heated all 5 tubes for 3 minutes in a boiling water bath, using a beaker, water, and
a hot plate. 5.Removed the tubes using tongs. Recorded colors on the following table. 6.Cleaned out the 5 test tubes with deionized water.


Benedict's Test Results

Discussion: From the results, the Benedict's test was successful. Onion juice contains glucose, and of course, glucose would test positive. Starch doesn't have a free aldehyde group, and neither does potato juice, which contains starch. Water doesn't have glucose monomers in it, and was tested to make sure the end result would be negative, a blue color.


Introduction:The iodine test is used to distinguish starch from monosaccharides, disaccharides, and other polysaccharides. Because of it's unique coiled geometric configuration, it reacts with iodine to produce a blue- black color and tests positive. A yellowish brown color indicates that the test is negative.

Materials: 6 barrel pipettespotato juicestarch solution 5 test tubeswateriodine solution onion juice
glucose solution5 toothpicks

Procedure: 1.Used 5 barrel pipettes, filled test tube #1 with onion juice, second...
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