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Experiment 4 Lab Review

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Experiment #4 (10/31/14) Lab Review

Objective
To introduce the basic molecules of life and to test for their presence in different substances.
Introduction
Macromolecules are in all forms of life. These organic compounds are carbohydrates, lipids, proteins, and nucleic acids. These are monomers and they link together into long chains that form polymers. Different reagents can be used to find the presence of these macromolecules.
Proteins are made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Proteins are covalently bonded in chains as polymers of amino acids. These bonds are called peptide bonds. Amino acids linked together form a polypeptide called a protein. Some proteins are also enzymes. The Biuret’s test is only for protein.
Carbohydrates contain carbon, hydrogen, and oxygen. They offer energy and also provide cell support in cells. There are three classifications for Carbohydrates: monosaccharides, disaccharides, and polysaccharides. Monosaccharides are the simple sugars. Two monosaccharides make a disaccharide. Three or more monosaccharides are a polysaccharide. Glucose, fructose, and galactose are monosaccharides. Sucrose, lactose, and maltose are disaccharides. Starch and glycogen are polysaccharides. Simple sugars can be found by using Benedict’s test. Starch will react with IKI to give a dark blue color change.
Lipids are macromolecules that are usually insoluble in water. Lipids are made of carbon, hydrogen, and oxygen. They are referred to as fats or triglycerides. Oils are liquid at room temperature and are called unsaturated. Solid fats are saturated. Lipids are found in cell membranes and are an energy source. By using the Sudan III test the presence of lipids can be found.
Data
Part 1 – Testing for Protein

Description
Observations
1
Egg white / albumin
Purple, 8 drops
2
Pepsin solution
Purple, 8 drops
3
Sugar
No color change
4
Water
No color change
The Biuret reagent contains sodium hydroxide and copper sulfate. The protein in an alkaline environment, reacts with copper sulfate to reduce the copper resulting in the color change.
Part 2 - Testing for Sugars
1.
Glucose
Red
2
Potato starch
Green
3
Onion juice
Blue
4
Water
Blue
Discussion
During the protein tests we tested for protein with the Biuret’s solution. All proteins are polymers of amino acids, covalently bonded in long chains called peptide bonds. Proteins and peptides react with the Biuret reagent. This reaction is specific for compounds with more than two peptide bonds. Biuret reagent is a mixture of a strong solution of sodium or potassium hydroxide and small amount of very dilute copper sulfate. The Biuret results with positive reactions to Albumin (egg white) and the enzyme, pepsin.
In the carbohydrate tests for simple sugars the results were what was expected of the Glucose + Benedict’s solution. Glucose is a simple sugar and all reducing sugars have an aldehyde functional group as part of their molecular structure, and this makes them react with Benedict’s reagent when heated. Reducing sugars accepts an oxygen atom from Benedict’s reagent and causes the reagent to be reduced. A greenish precipitate indicates about 0.5 g% concentration; yellow precipitate indicates 1 g% concentration; orange indicates 1.5 g% and red indicates 2 g% or higher concentration.
We did not perform the test for starch but when stained with the IKI solution. The potato slice would have shown dark blobs without really seeing any cells. The onion slice should have yield white cells visible. Glucose is a monosaccharide, sucrose is a disaccharide, and the starch solution is a polysaccharide. Iodine reacts with starch resulting in a dark, blue-black color that is a positive test for starch. Onions do not have starch and potatoes do.
The Sudan III test for Lipids would have yield positive results of staining red for the onion and slightly for the oil. Lipids are non-polar and they are insoluble in water or other polar liquids. They are soluble in non-polar solvents such as chloroform.

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