Macromolecules Lab Report

Introduction The purpose of this lab is to use control variables to help identify different macromolecules. Biological systems are made up of these four major macromolecules: carbohydrates, lipids, proteins and nucleic acids. Carbohydrates are sugar molecules (monosaccharides, disaccharides, and polysaccharides) which make them the most abundant macromolecule on the earth. Lipids (oils and fats, phospholipids and steroids) are insoluble in water and perform many functions such as energy source, essential nutrients, hormones and insulators (Lehman, 1955). Proteins are made up of peptide bonds holding amino acids together to perform biological functions like enzymes, antibodies, for transport and structure (Asmus, 2007). Lastly, nucleic acids

The iodine test determines the presence of starch in biological materials. It is predicted that, if starch is not present, the solution with iodine remains yellow. However, if starch is present the solution with iodine becomes a blue-black colour. Plants have starch as the storage polysaccharide (glucose units held together by glycosidic bonds) while animals have the equivalent of glycogen. In this experiment, the dark blue colour is visible because of the helical amylose and amylopectin reacting with iodine (Travers et al., 2002). The starch-iodide complex forms because of the transfer of charge between the starch and iodide ion and results in spacing between the energy levels. This allows the complex to absorb light at different wavelengths resulting in a dark blue colour (Travers et al., 2002). A blue colour would indicate a positive test while a yellow colour would show a negative test.
The Benedict’s test is useful for reducing sugars. Reducing sugars are a carbohydrate that can either be straight chains with an aldehyde group at the end or as ring forms with a ketone group (Hill, 1982). Monosaccharides and most disaccharides will reduce copper (II) sulfate. The Benedict’s solution contains cupric ions and the aldehyde groups at the end of the sugars will reduce the cupric ions to cuprous ions (Cu+). There will be a precipitate of copper (I) oxide when the cuprous ions combine with oxygen (Hill,

1% glucose, 1% maltose and 1% lactose all progressively get positive results by changing colours to reddish brown at the end of this experiment. In this case the aldehyde functional group that is present in the products (monosaccharides and some disaccharides) in this reaction is able to reduce copper in the presence of alkali and this produces colour changes while converting to an aldose sugar. Honey is made of fructose and glucose which instantly turned brown after the test-tube was placed in the boiling water because of its active aldehyde and carbonyl group. The copper (II) sulphate present in the Benedict’s solution reacts with electrons from the aldehyde group which results in a redox reaction to from cuprous oxide, a red brown precipitate that seen in all of the above mentioned solutions (Hill, 1982). Beer also gave positive results because it contains aldehydes and ketones (i.e. acetone, trans-2-butenal, furfual) during its beer production process where the sugars are converted through fermentation (Hill, 1982). As a result, beer attained a positive result. Starch and glycogen produced a negative result because they are polysaccharides and don’t have the aldehyde functional group. Distilled water contains no monosaccharides and has to ability to reduce the copper ions (Cu+) and