CARBOHYDRATES:
Learning objective
to be able to:
• Identify the elements that make up
carbohydrates
• To describe how monosacharides are
the basic molecular units of
carbohydrates.
• Explain how the condensation of
monosacharides forms disacharides
Fill in the table. Place a tick in the box if the statement is
correct, place a x in the box if it is incorrect.
Statement
Starch
Cellulose Glycogen
Storage molecule in plants

x
x
Polymer of beta glucose
Strengthened by thousands
of hydrogen bonds
x
x


x
x
A mixture of two
polysaccharides

x
x
x
x
x
Only found in fungi
Homework
1) Which three elements are found in carbohydrates?
Carbon, hydrogen and oxygen
2) Give two examples of how carbohydrates are used in the body.
Immediate energy, storage molecule
3) What is a polymer?
Large organic molecule formed by combining many smaller molecules
(monomers) in a regular pattern.
4) What is the general formula of a monosaccharide?
(CH2O)n
5) What would be the formula of a pentose sugar where n is 5?
C5H10O5
6) Fill in the gaps
Sugars, starches and cellulose are all examples of
monosaccarides are white and crystalline and
carbohydrates._______________
sweet tasting solids which __________
dissolve in water. They can be
classified according to the number of ________
carbon atoms present
in the molecule. Sucrose and Maltose are formed when two
monosaccharides join together in a condensation
____________ reaction. The
bond that is formed is called a ___________
glycosidic bond. Sucrose is
formed when a molecule of glucose
_________ bonds with a molecule
of _________.
fructose Maltose is formed from two molecules of
glucose
_________.
Disaccharides can be broken down into
monosaccharides by a ____________
hydrolysis reaction.
7) Distinguish between:
a) α glucose and β glucose
α glucose found in starch and glycogen, β glucose found in
starch, also orientation of OH group on Carbon 1
b) Cellulose and glycogen
Cellulose found only in plants, made of sheets of β glucose,
glycogen made by animals as their storage polysaccharide, poly
(1-4) α α glucose with 9% (1-6) branches
c) Amylose and amylopectin.
•Amylose is a straight chain poly-(1-4) glucose which coils up into a
helix. Amylopectin is poly(1-4) glucose with about 4% (1-6) branches
1. What is the molecular formula of a triose monosaccaride?
•
C3H6O3
CH2OH
2. Draw the structural
H
C
O
OH
formula of β-glucose
H
3. What would be produced
C
C
by the hydrolysis of sucrose?
OH
H
•
Fructose and glucose
C
C
H
•
List three properties common OH
H
OH
4. to all monosaccarides and
disaccharides
– Sweet tasting, soluble, crystalline, white
5. Name 2 structural features of starch that make it a good energy
storage molecule
– Insoluble
– Compact
6. Name a polysaccharide made from β-glucose
•
Cellulose
A key which is used to identify five different types of carbohydrate
is shown below:
carbohydrate
insoluble
Contains 1-6
glycosidic bonds
Found in
animals
A
glycogen
soluble
Does not contain
1-6 glycosidic
bonds
Contains
hydrogen
bonds
B cellulose
Transport
carbohydrate
in plants
Does not
contain
hydrogen
bonds
D sucrose
C amylose
Work out the molecular formula for maltose
C6H12O6 + C6H12O6 – H2O  C12H22O11
Component of
DNA
E
deoxyribose
Card sort
CH2 OH
O
HOH2C
CH2OH
O
Fructose
OH
Galactose
OH
OH
CH2 OH
CH2 OH
O
O
OH
α glucose
OH
β glucose
OH
OH
Biochemical tests
• All monosaccharides and some disaccharides
including maltose and lactose are reducing sugars.
• These can be tested for, by adding Benedict's
reagent to the sugar and heating in a water bath.
• If a reducing sugar is present, the solution turns
green, then yellow and finally produces a brick red
precipitate.
• Non-reducing sugars can also be tested for using
Benedict's reagent but first require addition of an
acid and heating to hydrolyse (break apart) the
sugar.
• The acid must then be neutralised using an alkali like
sodium hydroxide before carrying out the test as
described above.
Starch and cellulose
• Starch and cellulose are polysaccharides made from
the monosaccharide glucose by a series of
condensation reactions.
• In this activity, you will investigate the formation of
these polysaccharides.
represents
CH2OH
H
α
C
H
H
glucose
C
OH
HO
O
OH
C
OH
H
C
C
H
OH
OH
CH2OH
H
C
OH
β
HO
O
OH
H
glucose
C
represents
OH
C
OH
H
C
C
H
OH
H
Starch
• On the sheet of α-glucose structures, label the
carbon atoms and number them.
• Cut out each α-glucose unit and, on the top of a plain
sheet of paper, place four together in an amylose
configuration (use the paper in landscape mode).
This involves only 1,4-glycosidic bonds.
• Circle the parts of the molecules where the
condensation reaction will occur.
• Place some more α-glucose units on the lower part
of the paper in a chain and then add a 1,6-glycosidic
bond to make a branch to the structure. This is
amylopectin. Once again, show where the
condensation reactions take place.
Cellulose
• On the sheet of β-glucose structures, label the
carbon atoms and number them.
• Cut out each β-glucose unit and place six of them on
to a piece of paper in a chain. The chain must end
up in a straight line and you will need to think
creatively how to do this.
• Discuss your ideas and ask if you have the correct
solution before finally sticking the pieces in place.
• As for starch, circle where the condensation
reactions occur.
• Make a second chain parallel to the first. Where OH
and H groups are close together they are attracted
and hydrogen bonds form. Draw these bonds in with
a pencil.