MACROMOLECULES LAB
Name __________________________ Hour ____
Most nutrition charts encourage you to include fats, carbohydrates, and proteins in your diet. In what ways are these types of
molecules important to the bodies of various living organisms?
Carbohydrates in living cells serve as a source of energy. They are composed of molecules such as glucose called simple
sugars (monosaccharides). Simple sugars can be combined in chains to form more complex carbohydrates such as sucrose
(disaccharides) and starches and cellulose (polysaccharides).
Proteins (composed of amino acids) perform a variety of functions in the cells of living organisms. They are important to
both the structure and function of cells. For example, proteins help form part of the cell membrane and the other cell organelles.
Special proteins called enzymes control the chemical reactions in cells. Hormones are proteins that coordinate and regulate the
activities of cells, tissues and organs. Proteins in the form of antibodies help fight disease. Proteins even carry oxygen around the
body. It is important to understand the many functions proteins perform in the bodies of living organisms.
Fats (lipids) play many roles in living organisms. A special two part fat is the main structural component of cell membranes
(phospholipids). Cholesterol (a type of lipid) is used to manufacture a number of important control steroids, like testosterone and
estrogen. Fat is also an energy source and can be stored in energy reserves. These energy reserves also provide padding for internal
organs.
The following lab techniques will acquaint you with some simple tests for these important biological molecules.
Problem: How can you determine the presence of a simple sugar, a starch, a protein, and a fat in an
unknown sample?
Procedure 1—Simple Sugars
1. Fill a 400 mL beaker ½ full with tap water. Place the beaker on the hot plate and bring the water temperature to at or
near boiling.
2. Set 6 test tubes in a test tube rack. Label tubes 1 - 6.
3. Add the following to the test tubes
Test tube 1
2 full droppers of 10% sucrose solution (about 2 cm full)
Test tube 2
2 full droppers of 10% lactose solution (about 2 cm full)
Test tube 3
2 full droppers of water (about 2 cm full)
Test tube 4
2 full droppers of 10% glucose solution (about 2 cm full)
Test tube 5
2 full droppers of 10% starch solution (about 2 cm full)
Test tube 6
2 full droppers of the unknown solution (about 2 cm full)
Keep the droppers
clean! Prevent cross
contamination!
4. Add 5 drops of Benedict’s solution to each of the six tubes.
5. Simultaneously place the 6 test tubes in a beaker of hot water for up to 5 minutes. Keep track of how long it takes for
each tube to change color.
6. Record the color changes, if any. If monosaccharides are present in the sample, the indicator will turn orange to
brick red. If disaccharide maltose or lactose is present, the indicator will turn green. Polysaccharides should
not affect the color of the indicator.
7. Clean and rinse the test tubes thoroughly using a test tube brush and soapy water in the sink.
Discussion 1—Simple Sugars
Test tube
Contents
Test tube 1
Test tube 2
Test tube 5
Test tube 6
Actual color change
Time in seconds
10% sucrose
solution
10% lactose
solution
water
Test tube 3
Test tube 4
Expected color change
10% glucose
solution
10% starch
solution
Unknown
solution
1) How long did it take for the color changes to occur?
2) Why do you think it was necessary for you to test a tube containing only water?
3) Was there a difference in color with the sugars? If so, why do you think this is?
4) Did the unknown substance contain simple sugars?
Procedure 2—Starch
1.
2.
3.
4.
5.
6.
7.
Add the following to the test tubes
Test tube 1
2 full droppers of 10% sucrose solution (about 2 cm full)
Test tube 2
2 full droppers of 10% lactose solution (about 2 cm full)
Test tube 3
2 full droppers of water (about 2 cm full)
Test tube 4
2 full droppers of 10% glucose solution (about 2 cm full)
Test tube 5
2 full droppers of 10% starch solution (about 2 cm full)
Test tube 6
2 full droppers of the unknown solution (about 2 cm full)
Keep the droppers
clean! Prevent cross
contamination!
8. Add 3 drops of iodine solution to each test tube. A blue-black color indicates the presence of starch.
9. Clean and rinse the test tubes thoroughly using a test tube brush and soapy water in the sink.
Discussion 2—Starch
Test tube
Test tube 1
Test tube 2
Test tube 3
Test tube 4
Test tube 5
Test tube 6
Contents
10% sucrose
solution
10% lactose
solution
Color change?
1) Did any of the 3 known substances give a positive test
for starch? If so, which one(s)?
2) Why do you think the tubes containing glucose, lactose,
and sucrose were necessary?
Water
10% glucose
solution
10% starch
solution
Unknown
solution
3) Did the unknown substance contain starch?
Procedure 3—Proteins
1. Place 2 droppers full of egg white in test tube 1. In test tube 3 place 2 droppers full of water. In test tube 6 place 2
droppers full of the unknown solution.
2. Add 10-20 drops of Biuret solution to each test tube. If protein is present, the Biuret solution will turn purple/pink.
3. Clean the test tubes thoroughly in the sink.
Discussion 3—Proteins
Test tube
Contents
Test tube 1
Egg white
Test tube 3
water
Test tube 6
Unknown
solution
1) What can you conclude out egg whites from this
procedure?
Color change?
2) Did the unknown solution contain proteins?
Procedure 4—Fats
1. Place a drop of olive oil and a drop of water on separate pieces of brown paper allow to dry. Spread the drops out so
they will dry quickly.
2. Place a drop of the unknown solution on a piece of brown paper. Spread the drop out so it will dry quickly.
3. Once dry, hold up the brown paper so that a light is behind it and see if the light shines through.
1.
2.
3.
4.
OR
In test tube 3, place 2 droppers full of water.
In test tube 4, add 2 droppers full of olive oil.
In test tube 6, add 2 droppers full of the unknown solution.
Add 20 drops of Sudan IV. If lipids are present the Sudan IV will stain them reddish-orange (positive test).
Discussion 4—Fats
Test tube
Contents
Test tube 3
water
Test tube 4
Olive oil
Test tube 6
Unknown
solution
1) Did the unknown substance contain fat?
Color change?
--------------------------------------------------------------------------------------------------------------------Results: Mark yes or no for each solution.
Simple sugars?
Solution 1
Solution 2
Solution 3
Solution 4
Solution 5
Solution 6
Complex sugars
(starch)?
Proteins?
Fats?
Choices:
Water
Coke
Sierra Mist
Malted Milk powder in water
French salad dressing in water
Meat tenderizer in water
Olive oil
Egg whites in water
Answers:
Solution 1: Water
Solution 2: Malted Milk powder in water
Solution 3: Coke
Solution 4: Egg whites in water
Solution 5: French salad dressing in water
Solution 6: Meat tenderizer in water
Solution 7: Sierra Mist
Solution 8: Olive oil
Sugar
Dietary Protein
fiber /
starch /
complex
carbs
Fats
Yes -14g
Yes -27g
Yes -1g
Yes -1g
Yes
Yes -8g
Yes
Yes -26g
Yes -2g
Yes
Yes -14g
Benedict's reagent
From Wikipedia, the free encyclopedia
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Benedict's reagent (also called Benedict's solution or Benedict's test) is a chemical reagent named after an
American chemist, Stanley Rossiter Benedict.[1]
Benedict's reagent is used as a test for the presence of reducing sugars. This includes all monosaccharides and
the disaccharides , lactose and maltose. Even more generally, Benedict's test will detect the presence of
aldehydes (except aromatic ones), and alpha-hydroxy-ketones, including those that occur in certain ketoses.
Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a
positive test because it is converted to the aldoses glucose and mannose by the base in the reagent.[2].
One litre of Benedict's reagent can be prepared from 100 g of anhydrous sodium carbonate, 173 g of sodium
citrate and 17.3 g of copper(II) sulfate pentahydrate.[3] It is often used in place of Fehling's solution.
Benedict's reagent contains blue copper(II) ions (Cu2+) which are reduced to copper(I) (Cu+). These are
precipitated as red copper(I) oxide which is insoluble in water.
Chemical test
To test for the presence of monosaccharides and reducing disaccharide sugars in food, the food sample is
dissolved in water, and a small amount of Benedict's reagent is added. During a water bath, which is usually 410 minutes, the solution should progress in the colors of blue (with no glucose present), green, yellow, orange,
red, and then brick red or brown (with high glucose present).[4] A color change would signify the presence of
glucose. The common disacharrides lactose and maltose are directly detected by Benedict's reagent, because
each contains a glucose with a free reducing aldehyde moiety, after isomerization.
Sucrose (table sugar) contains two sugars (fructose and glucose) joined by their glycosidic bond in such a way
as to prevent the glucose isomerizing to aldehyde, or the fructose to alpha-hydroxy-ketone form. Sucrose is thus
a non-reducing sugar which does not react with Benedict's reagent. Sucrose indirectly produces a positive result
with Benedict's reagent if heated with dilute hydrochloric acid prior to the test, although after this treatment it is
no longer sucrose. The acidic conditions and heat break the glycosidic bond in sucrose through hydrolysis. The
products of sucrose decomposition are glucose and fructose, both of which can be detected by Benedict's
reagent, as described above.
Starches do not react or react very poorly with Benedict's reagent, due to the relatively small number of
reducing sugar moieties, which occur only at the ends of carbohydrate chains. Inositol (myo-inositol) is another
carbohydrate which produces a negative test.
Benedict's reagent can be used to test for the presence of glucose in urine. Glucose found to be present in urine
is an indication of diabetes mellitus. Once a reducing sugar is detected in urine, further tests have to be
undergone in order to ascertain which sugar is present. Only glucose is indicative of diabetes.