Name ________________
Date _____________
CHEMISTRY OF CARBOHYDRATES
Carbohydrates, fats proteins and nucleic acids are the four major groups of
organic molecules found in living organisms. Carbohydrates make up a large
group of organic compounds found in cells. They are generally used for energy
or cell structures.
With this lab exercise you will be expected to:
1. build on information about water in order to develop ideas about
carbohydrates
2. construct carbohydrate molecular models
3. be able to distinguish between models and actual chemical formulas or
molecules (structural and molecular formulas)
4. be able to determine the molecular characteristics of carbohydrates
Procedure
Students will work in groups of 4. Each student will be responsible for
filling out his/her own worksheet.
I-
CARBOHYDRATES: An important group of biological compounds are
the saccharides (the sugars of carbohydrates). Carbohydrates contain
carbon, hydrogen and oxygen. The many different types of sugars
have been grouped into three main categories:



A.
Monosaccharides or simple sugars
Disaccharides
Polysaccharides
Mono
Simple sugars or
saccharides:
a. Study the structures of the two monosaccharides below
Structural formula
for fructose
b. Construct the models for the two monosaccharides shown on
the previous page. Two members of the group should build one
while the other two members build the other.
The models constructed represent the 3 dimensional shapes of the molecules.
They illustrate that individual molecules of carbohydrates DO differ from one
another in general structural shape even though their molecular formulas are the
same. They also will illustrate how it is possible for molecules to join together to
form different carbohydrates.
c. How many atoms of carbon are there in each molecule of
glucose?
d. How many atoms of carbon are there in each molecule of
fructose?
e. Write the molecular formulas for
i. Glucose:
ii. Fructose
f. Compare the number of hydrogen atoms to the number of
oxygen atoms in each sugar. What is the ratio of hydrogen to
oxygen? (i.e.: how many hydrogen atoms are there for each
oxygen atom?)
g. How do they compare to the ratio in water?
-The structural arrangement of C, H and O in glucose and fructose differs. This
helps explain why different model shapes are used for each monosaccharide.
-Molecules of monosaccharides may have the same molecular formula but differ
in three-dimensional structures. This is called ISOMERISM. Using the two
models and structural formulas, describe isomerism in your own words. We saw
a similar word when we worked with C-12, C-13, C-14 and our Russian Spy who
was killed.
II-
DOUBLE SUGARS OR
DISACCHARIDES
Two monosaccharide molecules can chemically join together to form a
large carbohydrate molecule called a double sugar or disaccharide.
When a glucose molecule chemically joins with another glucose
molecule, a double sugar known as maltose (found in corn syrup) is
formed. When a glucose molecule joins with a fructose molecule, a
different double sugar called sucrose (table sugar) is produced.
a. Construct a glucose and a fructose model (you should have these
already)
b. Attempt to join the two molecules and build a sucrose molecule. To
do so it will be necessary to remove an –OH end from one
molecule and an –H end from another to join the molecules.
c. The –OH and –H ends removed from the glucose and fructose can
now be joined to form what familiar compound. We put this in our
coffee and tea! Do it!
d. Write the molecular formula for sucrose.
e. What is the ratio of hydrogen atoms to oxygen atoms in sucrose?
f. How does this compare to the ratio found in glucose and fructose?
g. How many monosaccharide molecules are needed to build a
disaccharide molecule? ________________
III-
POLY
COMPLEX SUGARS OR
SACCHARIDES.
Just as double sugars were formed from two monosaccharide
molecules, complex sugars are formed when many single sugars are
joined together chemically. The exact number of glucose molecules
attached to form these polysaccharides is not known. The two most
common polysaccharides in biology are starch and cellulose. They
consist of LONG molecules of glucose chained together.
a. Construct a starch molecule by joining four glucose molecules.
This represents only a small part of a starch molecule because
starch consists of hundreds of glucose molecules.
b. What must be removed from the glucose molecules in order to join
them together?
c. Determine the molecular formula of starch from the molecule you
formed (4 glucose molecules).
d. How does the ratio of H to O atoms in starch compare to the ratio in
double sugars?
e. In single sugars?