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Published byBeatrice Montgomery Modified over 9 years ago
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All living organisms are composed of four classes of macromolecules: Carbohydrates Lipids Proteins Nucleic acid 2
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Carbon containing compounds are called organic compounds. Carbon is the backbone of organic molecules, but its only one of several important bioelements. These bioelements are hydrogen, nitrogen, oxygen, phosphorous and sulfur. 3
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The chemical properties of the different classes depend on the presence of specific functional groups: Aldehyde group Ketone group Carboxyl group Amino group 4
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Carbohydrates are the main energy storing molecules. Monosaccharide : monomers (glucose, ribose, galactose). Disaccharides: two monomers connected with glycosidic bond (sucrose, lactose). Polysaccharides: polymers; more than three monomers (starch). 5
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A. Benedict’s test for reducing sugars: The test depends on the presence of free Aldehyde or ketone group. Monosaccharides and some disaccharides have these groups free are called reducing sugars. Free groups found in reducing sugars will react with Benedict’s reagent (CuSo 4 which is blue in color with NaOH). The test is both qualitative and quantitative test; Small amount of reducing sugar green color. Large amount of reducing sugar red- orange color. 6
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7 Fill the test tubes with 1 ml of one of the following solutions. D.W glucose sucrose starch milk apple juice maltos e
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8 Fill each test tube with 3 ml of Benedict’s reagent Put the test tubes in boiling water for 5 minutes If color change to: Record your results in a proper table Yellow Orange Red Positive test for reducing. If color remains blue (the color of Benedict’s reagent) Negative result. Green
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9 D.W glucose sucrose starch milk apple juice maltose
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B. Lugol’s iodine test for starch Starch is a polysaccharide consisting of many glucose monomers linked together into long branching chains. It is the primary storage carbohydrate in plants. In the presence of iodine (I 2 -KI), a solution containing starch will turn blue-black in color. 10
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11 Fill the test tubes with 2 ml of one of the following solutions. D.W glucose sucrose starch milk apple juice Potato juic e
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12 A blue-black Add two drops of lugol’s iodine to each test tube. Record the result in the report. If color change to: Positive test for starch If color remains yellow - brown (the color of the iodine) Negative result.
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13 D.W glucose sucrose starch milk apple juice Potato juice
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Proteins are the key substances in the structural and physiological function of living things. Proteins are polymers of amino acids in which the carboxyl group of one amino acid is linked with the amino group of the next amino acid in a covalent bond called the peptide bond. A. Ninhydrin test for amino acids Ninhydrin reagent reacts with free amino groups i.e free amino acids to form a purple or violet colored substance. 14
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To each of the test tubes, add 10 drops of ninhydrin reagent and heat the test tubes in boiling water for 5 minutes (avoid inhaling, poisonous fumes). A purple color is the +ve result. Record the color of the tubes content in the lab report. 16
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B. Biruet test for polypeptides The test reveals the presence of peptide bond i.e. proteins Biuret reagent CuSo 4 reacts with the peptide bonds between the amino acids changing in color from light blue to violet under alkaline conditions. The intensity of the violet color is proportional to the protein concentration. In the test, Cu +2 must complex with at least four to six peptide bonds to produce a color. Biuret reagent does not react with free amino acids. Short peptides don’t react positively. 17
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18 Fill the test tubes with 2 ml of one of the following solutions. D.W Lysine starch albumine milk
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19 Fill each test tube with 2 ml of Biuret reagent 19 If color change to: Record your results in a proper table. Violet Positive test for Biuret test If color remains blue (the color of Biuret reagent). Negative result.
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20 D.W milk Lysine starch albumine
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Lipids are a heterogeneous group of compounds that are insoluble in water, but are soluble in organic solvents such as ether and acetone. There are three major classes of lipids: Neutral fats (triglycerides). Phospholipids Steroids A. Sudan red test for fats Sudan red is a lipid soluble dye, when added to a mixture of lipids and water, The dye will move into the lipid layer giving the lipid a red color. 21
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23 Add 10 drops of Sudan IV solution to the test tube and mix. Record your observations. Two layers are formed, the upper one is the lipid stained with Sudan red IV The water remains in the bottom layer
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