Macromolecule Analysis
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Section Number: 005
130 L September 28, 2010, 7:00PM – 9:50PM, Biology 2-149
Experiment Date: September 21, 2010
Introduction
The purpose of this lab experiment is to identify the types of macromolecules in the solutions supplied. Using the results of the known substances, the unknown may be predicted. This experiment also familiarize with the concept of treatment controls which are used to check if the experimental conditions and procedures were conducted correctly. A positive control displays that the procedure that is very similar to the actual experimental test. The experimental result is that which is hypothesized and done many times before. A negative control is a result which does not change the normal state or negative result. (Johnson and Besselsen, 2002) In this lab, we dealt with three biochemical processes including Iodine test, Benedict’s test, and Biuret test. The Iodine test reacts with starch forming a colour change. Starch is a polymer of glucose which is made up of two polymers, amylase and amylopectin. Glycogen is also a polymer of glucose which is made up of amylopectin. Amylose is an unbranched, helical molecule whose sugars are joined by α (1 → 4) linkages. Amylopectin is a branched helical molecule. The amylose forms helices where iodine molecules assemble, forming a dark blue/black colour. The amylopectin forms much shorter helices and iodine molecules are unable to assemble, forming a brown/orange colour. (Karp 2010) Benedict’s test is used to detect reducing sugars. Benedict’s reagent is clear blue but when combined and heated to boiling with a substance containing glucose in a chain form, the cupric ions are reduced to a cuprous form (Cu+ ) and then oxidized to form copper oxide (Cu2O). Copper oxide is a brownish-orange substance that is insoluble in water. A positive reaction in a Benedict’s Test is the change of the clear light blue solution to an opaque orange-brown solution in a boiling water bath. This color change indicates the presence of glucose in a given solution. A high concentration of reducing sugars generates the formation of a red precipitate; a lower concentration produces a yellow precipitate. Biuret test detects the presence of peptide bonds. The peptide bonds bond with the copper ions to form a violet Cu2+ peptide complex. All of these tests are considered semi-quantitative since there results are in a range of colour. In a positive test, a copper(II) ion is reduced to copper(I), which forms a complex with the nitrogens and carbons of the peptide bonds in an alkaline solution. A violet color indicates the presence of proteins. Quantitative is concerning something which can be measured. The yields from this experiment are only an approximation of the quantity of the substance and lack the precision of a quantitative result. (Griggs and Bray 2001)
