Name Lab section number 4. Questions (to be turned in at the end of lab) 1. Prot
ID: 150735 • Letter: N
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Name Lab section number 4. Questions (to be turned in at the end of lab) 1. Proteins are made from amino acids. Why does the biuret reagent only detect protein but not amino acids? What kind of sugars does Benedict's reagent detect? What kind of sugars is the Benedict's assay insensitive to? Why? 2. 3. Disaccharides and starches are all made by polymerizing monosacharrides. Why does Lugol's reagent only detect starches but not sucrose? Human nutrition is essentially the study of how to best supply your body's cells with the molecules needed for normal operation. Can you think of any molecules or nutrients that your body needs besides the four major classes of biological macromolecules? 4.Explanation / Answer
Biuret test detect the presence of peptide bond. Peptide bond is bond formed between -NH3 group of one amino acid and -COOH group of another amino acid. Only if protein (polypeptide chains) are present it can detect its presence. Amino acids alone do not contain any peptide bond of its own. Simple reducing sugars such as glucose are tested using Benedict's test using Fehling's solution. Non-reducing sugars such as sucrose are insensitive to benedict's test since it contains two sugars (fructose and glucose) joined by glycosidic bond in a way to prevent the glucose isomerizing into aldehyde or fructose into alpha-hydroxy-ketone form. Therefor, sucrose being a non-reducing sugar cannot react with Benedict's reagent. Lugol's test is for strach detection. This is because iodine dissolved in an aqueous solution of KI reacts with starch. This reaction of the formation of polyiodide chains from the recation between starch and iodine. The amylose, or straight chain portions of starch gives dark blue colour on reaction. The amylopectin or branches side chains causes the formation of orange colour. Sucrose is a diasaccharide which doesnot contain the branches side chain and it does not react with KI to form comoplex. Major nutrition of human consists of four most important biological macromolecules. These are Proteins, carbohydrates, Lipids and Nucleic Acids. Proteins are linear polymers built of monomers unit called amino acids. It is the building block of hair, blood cells, muscles and enzymes. Carbohydrates nature depends of the number of sugar combined together and their orientation. we use the source of carbohydrates as a source of energy. Lipids is used as stored fat. it has important role in vitamin absorption, blood clotting etc. Nucleic acids are not used for energy but for string important genetic information in the form of DNA and RNA.
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