Carbohydrates
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CH2O is the generalized molecular formula
o Ex. Glucose C6H12O6 or sucrose
The function of carbohydrates is to be a source of energy for cellular respiration
Carbohydrates do not provide as much energy per gram as lipids, but because of their solubility they can easily
dissolve into cells and be transported into body fluids.
The molecules are hydrophilic (water-loving)
There are three categories of carbohydrates;
o Monosaccharides, disaccharides and polysaccharides
Ribose a PENTOSE sugar containing 5 carbons.
o The formula for ribose is C5H10O5
o Usually links up to phosphate group in DNA or RNA (both OH’s down on C-2 & C3)
o Not a true monosaccharide because does not form chains with itself
o Four carbon atoms are in the ring and 1 is in a side chain
o The carbon atoms are numbered starting to the right away from the side chain
o The hydroxyl group (OH) on carbon atoms 1, 2, 3 point up, down, down respectively.
A. MONOSACCHARIDES

Hexose monomer (mono = 1 unit) molecules which are the “building blocks” of carbohydrates. There are
3 hexose monosaccharides and they are isomers of each other.
o
Isomers are molecules which have the same molecular formula
Name
Molecular Formula
Structural Formula
Glucose
C6H12O6
Galactose
C6H12O6
Fructose
C6H12O6
Interesting facts
5 carbon ring
Solid- straight chain
=aldehyde
5 carbon ring
Found in milk
4 carbon ring
Found in honey
B. DISSACCHARIDES:
 Formed when two monosaccharides chemically bond together by dehydration synthesis reaction
(removal of water)
 The two monosaccharides are held together chemically through a glycosidic bond
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Maltose: sugar in beer and malt vinegar
Glucose
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
Maltose
+
Water
+
Galactose

Lactose

Sucrose
+
Water
Sucrose: Table sugar
Glucose

Glucose
Lactose: Sugar found in milk
Glucose

+
+
Fructose
+
Water
Maltose, Lactose and Sucrose are all disaccharides with the formula C12H22O11 . Thus they are all isomers
of one another.
They are water soluble molecules due to their OH bonds they contain. A high electronegativity
difference exists making them polar covalent molecules (hydrophilic).
C. POLYSACCHARIDES
 They are polymers (large molecules with repeating monomer subunits called monosaccharides)
 They are so large that when ingested they have to undergo hydrolysis (addition of water) to break their
glycosidic bonds to become more useful in the body (with the appropriate enzyme)
 Polysaccharides are insoluble because they form a coil shape and OH is tucked
Glycogen
 Animals store this in the
liver and muscle cells
 Insoluble in water
 Made of repeating
glucose units in a
straight chain with
smaller side chains
 α 1-4 glycosidic on
straight chain
 α 1-6 glycosidic on side
chain
Amylose (Starch)
 A plant starch
 Insoluble in water
Amylopectin
 A plant starch
 Insoluble in water
 Linear unbranched chain of
several hundred glucose
units
 α 1-4 glycosidic on straight
chain
******Alpha glucose
(2C’ OH down)
vs.
Cellulose
 Plant polysaccharide
 Insoluble in water
 Branched chains of glucose.
 Every 30th glucose has a side
chain bonded to α 1-6
glycosidic
 Chain of β-glucose units.
Has a flip flop pattern of
bonding that produces a
long rigid molecule. The
absence of side chains
allows linear molecules
to lie close together.
 Allows for H-bonding
which creates elongated
fibrils in plants
1-4 β glucose
beta glucose (2C’ OH up)