BIOL130L Study Guide - Final Guide: Biuret Test, Paper Chromatography, Iodine Test

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Ensures that any changes in the experiment were as a result to the actual experimental results: these controls can be positive or negative. A positive control = designed/prepared in such a way that the sample. Starch is a mixture of 2 different polymers (amylose and amylopectin: amylose is an unbranched helical molecules with alpha 1,4 linkages, amylopectin is a branched straight molecule with alpha 1,6 linkages. Iodine solution reacts with the amylose to form the intense blue- black colour. Glycogen is similar to amylopectin but is more branched. Iodine solution reacts with glycogen"s multi-branched structure to form the less intense reddish-brown colour: negative result: substance remains yellow: The cupric ions of the benedict"s test will react with the free aldehyde groups at the end of the straight-chain sugar to reduce the ions into cu+ Also bear in mind, substances like fructose with free ketone group can also reduce benedict"s solution: positive result:

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