Identifying The Presence Of Macromolecules In Salt Samples

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The objective in this experiment was to identify the presence of macromolecules in twelve samples using the iodine test, the Benedict test, and the biuret test. In the iodine test, starch and glycogen are the polysaccharides that can be identified if the test is done properly, (Harisha, 2006). A positive control will give a positive result at the conclusion of this experiment. In the case of the iodine test, this positive control is a change in colour when a polysaccharide of starch or glycogen is present. The solution used for this test is a very pale yellow and will turn blue-black when starch is present and a reddish-brown when glycogen is present, (Harisha, 2006). Any other carbohydrates that are present in the sample will generate no…show more content…
In the iodine test, there was a negative result because no change in colour was observed, as was the same for the biuret test. However, in Benedict’s test, the sample formed an opaque red precipitate at the bottom with a translucent brown red liquid on top indicating a positive result. This signified that sample one contained a reducing sugar. The glucose in the solution is an aldose that has an aldehyde group at the end of its structure, (Berg, Tymoczko, Stryer, 2002). This caused the glucose to react with the solution in Benedict’s test to form a precipitate as the cupric ions reacted with the open aldehyde groups. Sample two was 0.3% of glucose-1-phosphate. A negative result was given after all three tests were conducted. This is because in the iodine test and biuret test, glucose-1-phosphate contains no starch or glycogen and no proteins. From its name, one would assume that in Benedict’s test, sample two would yield a positive result. But since the glucose molecule has phosphorylated, the aldehyde on the end is no longer available for Benedict’s test to react with, and therefore indicates that there is no reducing sugar in the solution, (Alberts et al.,…show more content…
This shows that sample five had no presence of protein, starch, glycogen, or reducing sugars. Sucrose is a type of non-reducing sugar because it does not contain an aldehyde or ketone group for Benedict’s test to react with, (Ball, Hill, Scott, 2011). This disaccharide has a head to head glycosidic linkage and therefore makes the carbon in sucrose unavailable for bondage, (Ball, Hill, Scott, 2011). From this linkage, sucrose cannot react with Benedict’s test like all the other sugars. As a result, sucrose has no effect during all three experiments. Sample six was a 1% lactose solution that had no reaction with the iodine or biuret test. In Benedict’s test, the result was inconclusive as human error occurred causing the test tube to break during the boiling stage. An expected result is that lactose is a disaccharide that contains an aldehyde group and if the experiment went through, there would have been a colour change during Benedict’s test, (Ball, Hill, Scott, 2011). This colour change would have been an opaque red precipitate at the bottom of the test tube with a translucent brown red liquid on

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