Biological Molecules - Lab Report Example

Biological Molecules Introduction: Common biological molecules include carbohydrates, lipids and proteins. Carbohydrates include such compounds as saccharides, or sugars, and polysaccharides such as starch. Lipids are typically molecules whose structure is mainly hydrocarbon in nature, and includes such things as the fatty acids, cholesterol and many other such compounds. Proteins are compounds made up of a number of amino acids bonded together in a polymer-like head-to-tail manner. Each class of biological molecules has certain chemical characteristics that are due to the presence of specific functional groups within their molecular structures.

Because the functional groups exhibit characteristic chemical reactions that involve color changes, they can be used as the basis of both qualitative and quantitative assessments. Results:Benedicts TestsSample(B = Benedicts soln)Colour of Heated Reaction+/-Structure of Reacting Functional GroupDistilled water + Blt. blue (no change)-noneGlucose soln. + BRust red+O || -C-HSucrose soln + Blt. blue-noneStarch soln + Blt. greenish brown+O || -C-HOnion soln + Blt. orange+O || -C-HPotato soln + Blt.

greenish brown+O || -C-HIKI Starch Tests:TT#ReactantsPredicted Color ResultsStructure of Functional Group1Starch + IKIdk. red-brownStarch + I22Distilled water + IKIyellownone3Glucose soln + IKIyellowNo reaction4Rice solution + IKIred-brownStarch + I25Onion + IKIyellowNo reaction6Potato soln + IKIred-brownStarch + I2Brown Paper TestSample+ / -Structure of Functional Groupoil+Fatty acid triglycerideswater-nonePotato chip+As per oilcheese+As per oilSalad dressing+As per oilvinegar-None (CH3COOH and H2O)mustard+As per oilketchup-noneavocado+As per oilOrange juice-noneBiurets TestBiochemical testColor resultReacting groupWater + Biurets solnVery light bluenoneAlbumin soln + Biurets solnpurpleO O|| ||-C-NH-C-Starch + Biurets solnlt.

bluenoneGrannys Imitation Crab Meat ExperimentMash a sample of the imitation crab meat in some water with the homogenizer. Remove some of the liquid and place it in a clean test tube or other suitable glass container. To another such container add the equal amount of plain water. Test both solutions with diabetic glucose tests strips. Add Benedicts solution to both containers and heat using water bath. Observe color change identifying presence (or absence) of glucose in solution. A positive result with the water extract indicates that the imitation crab meat contains additional glucose and should be avoided by Granny.

Questions1. Samples should be heated in Benedicts test to increase the rate of the reaction between the sugar and Benedicts reagent. Without heating the reaction may proceed only very slowly, which may lead to a false result.2. The copper ions in the copper sulfate of Benedicts reagent bond non-covalently or coordinate to the aldehyde functional group of glucose and similar sugars. This facilitates an oxidation of the organic molecule to the carboxylic acid, and is accompanied by the formation of atomic copper by reduction of the copper ions.

The presence of copper atoms in the solution is responsible for the observed color changes. Similarly, the copper ions in Biurets solution coordinate to an amide linkage of protein to form a large complex ion that is highly colored. The IKI reagent in the starch test can be thought of as a complex of potassium ions and iodide ions that have captured molecules of iodine (I2). The multiple -OH groups presence on the starch molecules bond non-covalently to the iodine molecules to form a very dark colored complex.3. If KOH or NaOH were omitted from the Benedicts test, no result could be expected.

The hydroxide ion must be present to assist the opening of the ring structure of the sugar molecule so that the aldehyde functional group is free to react.4. Glycine is an amino acid and not a peptide or protein. It therefore does not have the amide or peptide structure necessary for formation of the colored complex ion that indicates a positive result in this test.5. Polysaccharides do not give a positive result for reducing sugars because an aldehyde functional group must be present in the molecule to be oxidized in reaction with copper ions.

Even though a polysaccharide is constructed from hundreds and even thousands of glucose (or other simple sugar) molecules, they are covalently bonded to each other as the ketal of the aldehyde functional group and so cannot react.6. Both negative and positive controls are required in order to define the limits of the test conditions. This is especially important if a color change reaction is being used to determine a quantitative rather than a qualitative value. The negative control provides the baseline value of the color change, and the positive control provides a functional indication of what to look for in the result of a test on an unknown compound.