CARBOHYDRATES
Properties
 Carbohydrates – Carbon/Hydrogen/Oxygen
 Formula – (CH2O)n
 Ratio: Carbon 1: Hydrogen 2: Oxygen 1
 USES: energy source, structural components, combination with
other compounds such as GLYCOPROTEINS
 ISOMERS are different structural arrangements of the same number
and types of atoms
Eg. C6H12O6 – glucose, fructose and galactose
 OPTICAL ISOMERS are identical in every way but are mirror images
of each other
Eg. α Glucose and β Glucose rings
Monosaccharides
•Simple sugars containing 3 to 7 carbon
atoms
•Primary energy source for fuelling cell
metabolism
•Reducing sugars and soluble in water
•Can bond together to form disaccharides
and polysaccharides
Egs. TRIOSE (3 carbon)
glyceraldehyde
*intermediate in carbohydrate
metabolism
PENTOSE (5 carbon)
ribose
*sugar unit of RNA
HEXOSE (6 carbon)
glucose
fructose
galactose
*energy
•Most pentose & hexose sugars can exist
in the form of rings and straight lines
- rings provide the sub-units
needed for building complex
carbohydrates
α- glucose & β- glucose differ in
the position of the –OH and –H
attached to the 1st carbon atom
(see above). This is an example of
an OPTICAL ISOMER
Condensation of Glucose/Fructose

When simple carbohydrates are joined to
make complex carbohydrates the process is
called CONDENSATION

Macromolecules (such as sucrose) are often
formed by removing ‘H’ from one atom and
‘OH’ from the other

The ‘H’ and ‘OH’ combine to form water

Monomers are joined to build
macromolecules by the removal of water

The reverse reaction when a polysaccharide
has water added and is broken down into
mono and disaccharides is known as
HYDROLYSIS
Eg. Sucrose (carbohydrate) is formed when glucose
and fructose are joined via a condensation
reaction

Energy is required to form the bond (anabolic)

The bond is known as an a
alpha (1-2) glycosidic bond
Disaccharides

Composed of 2 monosaccharides joined together by a condensation reaction

Joined by a GLYCOSIDIC BOND

Soluble in water
Eg. SUCROSE (glucose + fructose)
 table sugar
LACTOSE (glucose + galactose)
 milk
MALTOSE (glucose + glucose)
 grains
Polysaccharides

Polymers with monosaccharide sub-units, joined via condensation reactions
and glycosidic bonds

The polysaccharide can be made of several thousand monosaccharides
(forming a macromoleclule)

Poly saccharides are not sugars and are generally insoluble

Glucose accumulation will affect cell osmotic properties as well as reacting
with various chemicals
- therefore stored as a polysaccharide

Glucose can be made available again quickly by an enzyme controlled
reaction
Examples of Polysaccharides
STARCH
GLYCOGEN
(PLANT CARBOHYDRATE)
(ANIMAL CARBOHYDRATE)

Energy storage molecule in plants

Energy storage in liver and muscles of animals

Long chains of α- glucose molecules


Contains 25 – 30% AMYLOSE & 70 – 75%
AMYLOPECTIN
Branched polysaccharide composed of αglucose molecules with different links to starch

More water soluble than starch

Easily hydrolysed by enzymes into glucose

Easily hydrolysed into soluble sugars when
required

Chains can be branched or helixed
(amylopectin) or straight (amylose)
Examples of Polysaccharides
CHITIN
CELLULOSE
(ARTHROPOD EXOSKELETONS/FUNGI CELL WALLS)
(STRUCTURAL MATERIAL IN PLANT CELL WALLS)

Tough modified polysaccharide made
up of β-glucose molecules

Linear polysaccharide made of βGlucose joined by glycosidic links

Similar to cellulose but each glucose
has an amine (NH2) group attached

Most abundant organic material

Parallel chains become cross-linked
with hydrogen bonds and form
microfibrils

Microfibrils are very strong (major
structural component of plants)

Difficult to digest, humans cannot as
they lack relevant enzymes

Animals such as herbivores have
modified digestive systems that
harbour bacteria that can breakdown
cellulose

2nd most abundant carbohydrate
Cellulose cont.........
The nature of the glycosidic bond means that each glucose molecule is
180° rotated compared to those next to it (SEE ABOVE)
This gives cellulose its linear shape and strength
Allows many hydrogen bonds between parrallel cellulose chains
Cellulose cont.........
Hydrogen bonds between cellulose chains
Biological Macromolecules
Which of the following describe disaccharides?
A) Glucose, galactose, and fructose are isomers with more than one
asymmetric carbon.
B) They are a long chain of monosaccharides linked by glycosidic bonds.
C) Cellulose is the result of two monosaccharides that have undergone a
condensation reaction.
D) Lactose, maltose, and sucrose are the result of bonded monosaccharides
after a dehydration reaction.
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Biological Macromolecules
Which of the following describe disaccharides?
A) Glucose, galactose, and fructose are isomers with more than one
asymmetric carbon.
B) They are a long chain of monosaccharides linked by glycosidic bonds.
C) Cellulose is the result of two monosaccharides that have undergone a
condensation reaction.
D) Lactose, maltose, and sucrose are the result of bonded monosaccharides
after a dehydration reaction.
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Biological Macromolecules
Why are carbohydrates an essential part of our diets?
A) All of these answers.
B) Carbohydrates provide more energy than lipids.
C) Carbohydrates contain only soluble elements that are vital to the health of
our bodies.
D) Carbohydrates provide energy from our diets.
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Biological Macromolecules
Why are carbohydrates an essential part of our diets?
A) All of these answers.
B) Carbohydrates provide more energy than lipids.
C) Carbohydrates contain only soluble elements that are vital to the health of
our bodies.
D) Carbohydrates provide energy from our diets.
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