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Name ________________________________________________
Lab # _____________
Biochemistry
Introduction: As biologists, we depend on chemists for our understanding of how many chemicals play an
important role in the life processes. Carbohydrates, proteins, and fats are organic compounds made up of carbon,
hydrogen, and other elements. They are large molecules which are used by the cell for several purposes
including: an energy source for respiration, components of cell structures like the cell membrane, cell growth,
cell repair, energy storage, and catalyzing cellular chemical reactions.
Objectives:
A. To learn the molecular formulas of carbohydrates, proteins and fats
B. To make structural models of carbohydrates, proteins and fats
C. To use those models to demonstrate how complex carbohydrates are formed and
broken down in the body
D. To use various indicators to test for the presence of carbohydrates and proteins
Materials:
scissors
glue
hot water bath
test tubes
glucose solution
starch solution
protein solution
Benedict’s solution
Biuret’s reagent
Lugol’s iodine
Procedure:
1. Monosaccharides – Glucose is an example of a monosaccharide which means it is one simple sugar.
Fructose and galactose are also examples of monosaccharides. Examine the pictures of these monosaccharides
and answer the questions that follow.
Structural Formulas
A. What three elements are present in glucose, fructose and galactose?
_____________________
______________________
B. How many atoms of carbon are present in:
C. Write the molecular formulas for:
glucose?
fructose?
galactose?
glucose
fructose
galactose
_____________________
_____
_____
_____
C___H___O___
C___H___O___
C___H___O___
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D. How many times larger is the number of hydrogen atoms than oxygen atoms in each of these molecules of
monosaccharides? __________
E. How many times larger is the number of hydrogen atoms than oxygen atoms in a molecule of water, H2O?
__________
2. Disaccharides
A. Two molecules of sugar can be joined together by taking out water in a process called
_______________________________________.
B. Cut out a glucose and fructose paper model molecule and attempt to join the two molecules together
like puzzle pieces. Do they fit easily together?_____________
C. In order to join them, remove an -OH group from one and an -H group from the other. Now do they fit
easily together? _______________
D. When put together, glucose and fructose create a molecule of sucrose. In addition, removing an -OH and an
-H group has just formed what molecule? _______________
E. Glue the glucose and fructose models together as well as the molecule of water removed and fill in the
equation below.
Glucose + Fructose  ____________________________________ + _____________________
F. To determine the molecular formula
for sucrose, complete the following
equation:
Glucose
Fructose
+
C___H___O___
C___H___O___
equals
minus
-
C___H___O___
H___O___
equals formula for sucrose:
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C___H___O___
3. Polysaccharides – The prefix poly means many. Starch, cellulose, and glycogen are three polysaccharides
made of three or more molecules of simple sugars. Cut out three molecules of glucose and paste them below to
make a molecule of starch. Then, complete the formula.
glucose + glucose + glucose  _______________________ + _____ molecules of water
Determine the molecular formula for starch:
Glucose
Glucose
Glucose
+
+
C___H___O___
C___H___O___
C___H___O___
equals
minus
minus
-
C___H___O___
H___O___
H___O___
equals formula for starch:
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C___H___O___
4. Proteins – are made of chains of amino acids. Examine the amino acids below and answer the following
questions.
A. Which element is present in amino acids that was
absent from carbohydrates? ______
B. What is the formula for the following amino acids:
Glycine
C___H___O___N___
Alanine
C___H___O___N___
Threonine
C___H___O___N___
C. Are the molecular formulas for all amino
acids the same? ___________
D. Cut out the four amino acid molecules and remove
the water to join them together
in the following order:
Valine—Threonine—Alanine—Glycine
Paste them and the waters removed below:
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5. Lipids - are fats, waxes, and oils. They are made up of the alcohol glycerol and three fatty acids. Cut out the
glycerol and fatty acid molecules and remove the water to join them together. Paste the newly formed lipid and
waters removed below.
6. Carbohydrates, Lipids and Proteins cannot be observed with the naked eye. So how can we determine
what kind of compounds are present in the foods we eat?
Indicators - are chemicals that demonstrate color changes in the presence of certain molecules. Benedict’s
solution tests for the presence of simple sugars. Biuret’s reagent tests for the presence of protein. Lugol’s iodine
tests for the presence of starch. Follow the procedure below to observe both positive and negative tests using
these three indicators.
A. Label six test tubes #1-6.
B. Add the following substances to the test tubes and complete the chart below.
*Biuret’s reagent and Lugol’s iodine show a color change immediately. Any test tubes containing Benedict’s
solution must be placed in a hot water bath for a few minutes in order to see a color change.
Test
Tube
Contents
1
10ml water
10 drops Benedict’s solution (heat)
2
10ml glucose solution
10 drops Benedict’s solution (heat)
3
10ml water
10 drops Biuret’s reagent
4
10ml protein solution
10 drops Biuret’s reagent
5
10ml water
10 drops Lugol’s iodine
6
10ml starch solution
10 drops Lugol’s iodine
Color before
Indicator
(or heat)
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Color after
Indicator
(or heat)
Positive or
Negative
Test
Conclusion Questions:
1. How are glucose, fructose and galactose the same? How are they different? (Refer to page 1)
Same _____________________________________________________________________________
Different __________________________________________________________________________
2. How many simple sugars make a
3.
monosaccharide?
disaccharide?
polysaccharide?
_______
_______
_______
a. When joining monosaccharides to make larger molecules, what ends are removed?
__________ and __________
b. Together these form a molecule of ____________________.
4. a. Define dehydration _________________________________________________________________
b. Define synthesis ___________________________________________________________________
c. Put the two together to explain how a polysaccharide is made from many monosaccharides.
_____________________________________________________________________________________
_____________________________________________________________________________________
5. Potato plants carry out photosynthesis to make molecules of glucose. If they can’t use all the glucose they
make in a day, they store it as starch. Explain how they convert glucose to starch.
_____________________________________________________________________________________
_____________________________________________________________________________________
6. A few days later, a potato plant has not made enough glucose to feed itself for the day. Explain how it gets
glucose from the starch it is storing. (Include the name of the process it uses.)
_____________________________________________________________________________________
_____________________________________________________________________________________
7. In humans, and all multicellular organisms, starch (ex. Potatoes, pastas) must be digested into glucose.
Explain why: _______________________________________________________________________________
8. What molecules are needed to form a protein? _____________________________________________
9. All amino acids have an amino group (-NH2) and a carboxyl group (-COOH). So what is it that makes one
amino acid different from the other 19? __________________________________________________________
10. There are only 20 amino acids but thousands of different proteins. Explain.
_____________________________________________________________________________________
_____________________________________________________________________________________
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11. The ________________________________ of amino acids determines the _________________________
of a protein. The ____________________ of a protein determines its’ function.
12. When trying to determine which structure is a carbohydrate vs. a protein vs. a fat, what are the key
characteristics you look for?
Carbohydrate _____________________________
Protein __________________________________
Fat _____________________________________
13. Why can carbohydrates, proteins, and fats all be classified as organic molecules?
__________________________________________________________________________________________
14. In the chart below, answer “yes” where appropriate. (Do not write in NO – just leave blank).
Characteristic
Carbon present
Monosaccharides
Hydrogen present
Oxygen present
Nitrogen present
Organic compound
Twice the amount of hydrogen as
oxygen
20 different kinds
Glucose is an example
Building blocks of proteins
Valine is one example
Building blocks of complex
carbohydrates
Needed by ribosomes in a cell
End product of starch digestion
End product of protein digestion
Needed by cells to build enzymes,
hormones, antibodies, etc.
Used by cells for respiration
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Amino Acids
Lipids
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