Notes

Background
All organic molecules are made up of the basic elements: carbon, oxygen, hydrogen, and nitrogen. When these elements are arranged in different ways, they group together to form four general types of biological molecules with unique characteristics: carbohydrates, lipids, proteins, and nucleic acids.
In these lab experiments, you will test for the presence of these four biological molecules using some basic chemical test methods and techniques.
Carbohydrates: Sugars and Starches
Athletes and weightlifters seek out carbohydrates, which they commonly refer to as carbs, to help maximize their energy output and performance. Lately, certain fad-diets point to carbohydrates as the evil cause of weight gain for the average American. However, the fact is that the human cell efficiently stores energy for short term use in the form of carbohydrates. The most abundant biological molecule on the planet happens to be a carbohydrate in the structural form of cellulose. Cellulose is commonly found in trees as wood and in the stems of plants.
There are two major types of carbohydrates: sugars (monosaccharides and disaccharides), and complex sugars (polysaccharides).
The simplest sugars are monosaccharides, small molecules that are often covalently bound together to form larger molecules. The most common monosaccharide is glucose, which is a key player in many biological pathways. Monosaccharides are capable of reducing other compounds and are thus called reducing sugars.
Benedict's solution is a solution made up of copper ions dissolved in a neutral solution (a pH of 7). When mixed with Benedict's solution and heated, the double bonded oxygen (called a carbonyl) on the simple sugar gets reduced by the copper ions.ﾠ This reduction reaction causes the Benedict reagent to change color, varying from green to yellow to orange to red, depending on the quantity of sugars present in the solution.
Two monosaccharides can bind together to form a disaccharide. For example, if two glucose molecules bind together they form maltose. Because that bond contains the free carbon group that acts as a reducing agent in simple sugars, disaccharides do not test positive with Benedict's solution. Despite a few other differences, monosaccharides and disaccharides are chemically similar and thus are both classified as sugars.
benedicts_test
Monosaccharides can also bind together in long chains called polysaccharides or starches. Starches are chemically distinct from sugars. They can have different shapes based on the way the monosaccharide chains fold. The presence of starch can be detected by adding a solution of iodine potassium iodide (IKI). IKI by itself has an amber-yellow color, but when it interacts with a starch, the solution changes to a deep blue-black color.
starch_test
Lipids
Lipids are compounds that are insoluble in water, but soluble in organic solvents such as alcohol and ether. Lipids include fats, oils, phospholipids, steroids, and cholesterol. The fats that you are most familiar with are triglycerides. The "tri" in "triglyceride" represents the three fatty acids that bind to one molecule of glycerol (glyceride). Thus, lipids do not form polymers whereas carbohydrates and proteins do.
Sudan IV is a chemical that is not soluble in water, but is soluble in lipids. To test for the presence of lipids in a solution, you can use the Sudan IV test where a red color indicates the presence of lipids.
Proteins
Proteins are the most plentiful biological molecules in living cells. They have numerous functions in organisms, especially in the form of enzymes, or organic catalysts, which assist almost every chemical reaction that takes place in your body. Pepsin is a digestive enzyme active in the stomach. It helps to speed up the digestion of nutritional proteins.
Proteins are made up of amino acids. About twenty different amino acids are found in cells. All amino acids have an acidic carboxyl group (-COOH) and an amino group (H2N-). They differ from each other by the R group attached to the carbon atom. R groups vary in size, shape, and chemical activity.
Just as a long chain of monosaccharides forms a starch, a long chain of amino acids forms a polypeptide. The amino acids in a polypeptide are held together by peptide bonds that are formed between the COOH group of one amino acid and the (H2N) of another amino acid.
The function of a protein is determined by its three-dimensional shape. The shape is produced by the particular chemical interactions of the R groups in the protein.
Biuret reagent is used to test for the presence of proteins. It is a blue solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH), and a very small amount of copper sulfate (CuSO4). This reagent changes color in the presence of proteins because the amino group (H2N-) of the protein combines chemically with the copper ions in the Biuret reagent. The more peptide bonds that are present, the more intense the color change. In the presence of protein, the reagent turns violet. If proteins have been broken down into short peptide chains, the reagent turns pink.
biuret_test
Dulce Garcia
5:45pm
Dulce Garcia
experiment 1
TT1-Added 6 mL of 5% Glucose Solution
the color is transparent
TT2- Added 6 mL of Water
the color is transparent
Added 6ml of benedicts solution to each of the test tubes
tt1- the color changed to blue
tt2- the color changed to blue
placed two constant temperature baths
ctb1- 100c
cbt2- 100c
moved tt1 to cbt1, tt1 color changed to orange
moved tt2 to cbt2, tt2 color stayed the same
tt3- Added 6 mL of 5% Sucrose Solution
the color is transparent
tt4- Added 6 mL of 5% Fructose Solution
the color is transparent
Added 6 mL of Benedict's Solution to each test tube
tt3- the color changed to blue
tt4- the color changed to blue
tt3 stayed the same color
tt4 chaned to color orange
experiment 2
tt1- Added 6 mL of 2% Starch Solution
the color is transparent
tt2- Added 6 mL of Water
the color is transparent
Added 6 mL of Iodine Solution to each test tube
tt1- the color changed to grey/purple
tt2- the color changed to dark green/grey
experiment 3
tt1- Added 6 mL of Corn Oil
the color is dark green/grey
tt2- Added 6 mL of Water
the color is grey
Added 6 mL of Sudan Solution to each test tube
tt1- the color changed to red
tt2- the color is grey
experiment 4
tt1- Added 6 mL of Egg White solution
the color is transparent/grey
tt2- Added 6 mL of Water
the color is grey/transparent
Added 6 mL of Biuret Solution to each test tube
tt1- the color changed to purple
tt2- the color changed to blue
experiment 5
Potato Juice
tt1- Added 6 mL of Benedict's Solution
the color is blue
tt2- Added 6 mL of Iodine Solution
the color is green/grey
tt3- Added 6 mL of Sudan Solution
the color is transparent
tt4- Added 6 mL of Biuret Solution
the color is purple
Added 6 mL of Potato Juice solution to each test tube
tt1- the color changed to orange
tt2- the colro cahnged to black
tt3- the color changed to grey
tt4- the color stayed purple
Onion Juice
tt1- Added 6 mL of Benedict's Solution
the color is blue
tt2- Added 6 mL of Iodine Solution
the color is green/grey
tt3- Added 6 mL of Sudan Solution
the color is transparent
tt4- Added 6 mL of Biuret Solution
the color is purple
Added 6mL of Onion Juice solution to each test tube
tt1- the color changed to orange
tt2- the color stayed green/grey
tt3- the color stayed grey
tt4- the color changed to purple
Whole Milk
tt1- Added 6 mL of Benedict's Solution
the color is blue
tt2- Added 6 mL of Iodine Solution
the color is green/grey
tt3- Added 6 mL of Sudan Solution
the color is transparent
tt4- Added 6 mL of Biuret Solution
the color is purple
Added 6mL of Whole Milk to each test tube
tt1- the color styaed blue
tt2- the color stayed green/grey
tt3- the color changed to red
tt4- the color changed to purple
Skim Milk
tt1- Added 6 mL of Benedict's Solution
the color is blue
tt2- Added 6 mL of Iodine Solution
the color is green/grey
tt3- Added 6 mL of Sudan Solution
the color is transparent
tt4- Added 6 mL of Biuret Solution
the color is purple
Added 6mL of Skim Milk to each test tube
tt1- the color stayed blue
tt2- the color stayed green/grey
tt3- the color stayed grey
tt4- the color changed to purple