Unit 5: Review
Macromolecules Lab
I. Carbohydrates
Carbohydrates are composed of monomers called the monosaccharides, or simple
sugars.
Monosaccharides contain C, H. and O in a ratio of 1:2:1. Glucose, fructose, and
galactose are monosaccharides and have the molecular formula, C6H12O6.
Monosaccharides can be linked together to form disaccharides. Sucrose, maltose and
lactose are disaccharides. Sucrose is formed by the monosaccharides glucose and
fructose. Maltose is formed by two glucose molecules. Lactose is formed by the
monosaccharides glucose and galactose.
Linking more than two monosaccharides together forms a polysaccharide such as
starch, glycogen, or cellulose. Diagrams of these are found in your lab manual.
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Carbohydrates continued
Carbohydrates continued
Benedict’s test for reducing sugars
Monosaccharides contain a double-bonded oxygen atom that is present as a
carbonyl group. This group will react with Benedict’s reagent to form a precipitate
that varies in color depending on the sugar concentration. Some disaccharides will
also react with Benedict’s reagent when the bond between the monosaccharides is
broken leaving a free carbonyl group. No polysaccharide is a reducing sugar.
Testing for reducing sugars
The test tube rack contains substances that were tested in lab.
Pure starch, a polysaccharide, will test negative for reducing sugars. If starch is taken
from potatoes, their cells also contain enzymes (β-amylase) that breakdown starch
to maltose (disaccharide). Maltose is also tested along with starch in potato extract.
Sugars with free carbonyl groups are called reducing sugars. They cause the Cu 2+
in the Benedict’s reagent to become reduced (gain electrons) to form Cu 1+ ,
forming Cu2O. The reaction occurs when the mixture is heated to 100 °C.
Water
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Carbohydrates continued
sucrose
starch
Water
glucose
sucrose
starch
milk
apple
juice
potato
juice
Carbohydrates continued
Benedict’s reagent is added to each of the test
tubes.
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glucose
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The tubes were heated at 100 °C for 3 minutes.
milk
apple
juice
potato
juice
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Carbohydrates continued
Carbohydrates continued
Results were recorded
A color change to yellow, orange or red indicates a positive test for reducing
sugars. If test tube color remains blue (the color of Benedict’s reagent) it is a
negative result. If positive, the name of the reducing sugar must be determine.
An unknown substance was tested. Does it contain a reducing sugar? If so, provide
the name of the reducing sugar (by comparing it to the prior test tubes),
Unknown
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Water
glucose
sucrose
starch
milk
apple
juice
potato
juice
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Carbohydrates continued
Carbohydrates continued
Iodine test for starch
Starch is a polysaccharide consisting of many glucose monomers linked together
into long branching chains. It is the primary storage carbohydrate in plants. In the
presence of iodine (I2-KI) a solution containing starch will turn blue-black in color.
Iodine is added to each of the test tubes. A color change
to blue-black indicates a positive test for starch. If test tube
color remains yellow-orange (the color of iodine) it is a
negative result.
The test tube rack contains substances that were tested in lab.
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Water
glucose
sucrose
starch
milk
apple
juice
potato
juice
Continue
Carbohydrates continued
An unknown substance was tested and the test tube is below. Does it contain
starch?
Water
glucose
sucrose
starch
milk
apple
juice
potato
juice
II. Lipids
Lipids are a structurally diverse group of substances that are classified together
because they are all insoluble in water (hydrophobic). When mixed with water, lipids
clump together as a result of hydrophobic interactions. Lipids include fats, oils,
steroids, and waxes. Fats and oils are high-energy compounds containing twice the
energy per gram as a carbohydrate. Fats are the primary energy storage molecule
in animals and also provide thermal insulation and padding.
Fats and oils consist of glycerol and fatty acids. Glycerol is a three-carbon alcohol.
Fatty acids are carboxylic acids that contain hydrocarbon chains that generally
vary in length from three to eighteen carbons. Fatty acids can also vary in the
number and position of carbon-carbon double bonds in the hydrocarbon chain.
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Fatty acids without carbon-carbon double bonds are classified as saturated,
whereas those with at least one carbon-carbon double are classified as
unsaturated. Saturated fatty acids are solids at room temperature. Grease, lard,
and butter are examples of fats containing saturated fatty acids. Unsaturated fatty
acids are less dense than saturated fatty acids, have lower melting points, and tend
to be liquids at room temperature. Fats composed of unsaturated fatty acids are
referred to as oils, such as corn oil.
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Lipids continued
Lipids continued
Sudan IV test for lipids
The test tube contains water.
Detergent water was added to the test tube and mixed.
Detergent is an emulsifier. It surrounds the oil droplets and
allows them to stay suspended in the water. The suspended oil
droplets stained with Sudan IV give color to the solution.
Drops of vegetable oil were added to the test tube. The
two liquids do not mix after shaking the test tube because
the oil molecules are hydrophobic (insoluble in water). This is
an emulsion.
After the test tube sits, the oil will separate from the water.
Sudan IV is a red stain. Drops of Sudan IV were added to the test tube
containing water and oil. The tube was mixed. Observe which of the two
liquids the dye stains (is soluble in).
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III. Proteins
Proteins continued
Proteins are complex organic molecules composed of individual subunits called
amino acids. There are 20 different amino acids common to transcribing
polypeptides on ribosomes in all living organisms. These amino acids vary in their
characteristics. They all possess a central carbon atom to which are attached an
amino group (-NH2) and a carboxyl group (-COOH), as well as a H atom and an R
group that varies among amino acids. Proteins are formed by linking amino acids
together into chains by peptide bonds. See diagram in lab manual.
Biuret test for proteins
The test tube rack contains substances that were tested in lab.
In the presence of proteins, biuret reagent reacts with the peptide bonds
between the amino acids changing in color from light blue to violet. The intensity
of the violet color is proportional to the protein concentration. Biuret reagent does
not react with free amino acids.
Water
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Proteins continued
Biuret reagent is added to each of the test tubes. A color
change to violet (sometimes lavender to pink ,depending on
the protein concentration) indicates a positive test for protein. If
test tube color remains light blue (the color of biuret) it is a
negative result.
glucose
starch
egg
white
milk
bread
solution
Proteins continued
An unknown substance was tested and the resulting test tube is below. Does the
test tube contain protein?
Unknown
Water
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glucose
starch
egg
white
milk
bread
solution
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IV. Hydrolysis of macromolecules
Polymers are disassembled or broken down by the process of hydrolysis, as
bonds between monomers are broken by the addition of water. A good
example would be the digestion of the food we eat. Most of the food we
consume is too large to enter our cells. Enzymes within the digestive tract
hydrolyze the food into monomers that are absorbed into our blood stream for
distribution to all body cells. See diagram in lab manual.
Hydrolysis of starch
Hydrolysis of macromolecules continued
We have 3 test tubes of starch. To each test we added 2M HCl and Benedict’s
solution. One is not boiled, the second is boiled for 10 minutes and the third is
boiled for 20 minutes.
O min
1O min
2O min
Starch is a polysaccharide. The enzyme, amylase, can break down starch to
maltose, a disaccharide. The enzyme maltase can break down maltose to
glucose, a monosaccharide.
Hydrolysis of sucrose
Sucrose is a disaccharide. The enzyme sucrase can break down sucrose to
fructose + glucose, which are both monosaccharides.
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Did the starch hydrolyze with the addition of HCl but no heat?
Did the starch hydrolyze with the addition of HCl and heat? If so, how many
minutes of boiling did it take for hydrolysis to occur?
Hydrolysis of macromolecules continued
We have 3 test tubes of sucrose. To each test we added 2M HCl and Benedict’s
solution. One is not boiled, the second is boiled for 10 minutes and the third is
boiled for 20 minutes.
O min
1O min
2O min
Did the sucrose hydrolyze with the addition of HCl but no heat?
Did the sucrose hydrolyze with the addition of HCl and heat? If so, how many
minutes of boiling did it take for hydrolysis to occur?
End of Lab Review ☺
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