Chapter 5- The Structure and
Function of Macromolecules
Carbohydrates
AP BIOLOGY
1
Macromolecules
• Carbohydrates
• Proteins
• Lipids
• Nucleic Acids
2
Carbohydrates
3
Polymer Vs. Monomer
• Polymer: A large molecule
made up of identical or similar
building blocks
– Ex. Polysaccaride
• Starches
• Monomer: the building block
that is used to make polymers
– Glucose
4
Carbohydrates
• Carbohydrates are composed of C, H, O
• Most names for sugars end in –ose
• CH2O (Empirical Formula)
(CH2O)x
C6H12O6
(CH2O)
C6H12O6
• Contains a Carbonyl (C=O) & many Hydroxyl (OH)
• Function: Energy & Storage
• ex: sugars, starches, cellulose, chitin
Monosaccharides
• Simple 1 monomer sugars
• Ex’s:
– Glucose
– Frucotose
– Galactose
sugar
sugar
sugar
sugar
sugar
sugar
sugar
sugar
6
Biological function of monosaccharides
• ENERGY!!!!
• Key parts of other molecules (e.g. nucleic acids, ATP)
• Monomers for Disaccharides & Polysaccharides.
• They form polymers in dehydration reactions.
Classifying Monosaccharides
• Monosaccharides are uniquely identified based on:
– The location of the carbonyl carbon in the straight chain
form
– The number of carbons present
– The spatial arrangement of carbons
Sugar structure
5C & 6C sugars form rings in solution
Where do
you find solutions
in biology?
In cells!
Identifying monosaccharides
alpha-glucose
beta-glucose
• The arrangement of the –OH group on the #1
carbon does not matter when naming sugars.
• The location of the other groups on the 2,3,4, and 5
carbons does matter.
Carbons are numbered
C 6'
5' C
O
4' C
C 1'
energy stored in C-C bonds
C 3'
C 2'
Carbon Skeleton
• 3-7 Carbons long
• Classified by number of carbons
– 6C = hexose (glucose)
– 5C = pentose (ribose)
– 3C = triose (glyceraldehyde)
CH2OH
H
HO
CH2OH
O
H
OH
6
H
Glucose
H
H
OH
OH
C
O
H
HO
H
5
OH
O
HO
H
Ribose
H
H
C
H
H
C
OH
3
OH
H
Glyceraldehyde
Functional groups determine function
Aldehyde
Carbonyl at
end
Ketone
Carbonyl in
middle
Forming Disaccharides
glucose+ glucose=
monomer
monomer
Disaccharide
Polymer
14
Disaccharides
• 2 monomers
• Held by
glycosidic bonds
• Ex’s
– Sucrose
– Lactose
– Maltose
Disaccharide
Monosaccharides
Sucrose
Glucose
+
Fructose
Lactose
Glucose
+
Galactose
Maltose
Glucose
+
Glucose
15
Building sugars
Dehydration synthesis
monosaccharides
|
glucose
H2O
disaccharide
|
fructose
sucrose
(table sugar)
Building sugars
monosaccharides
disaccharide
H2O
glycosidic linkage
|
|
glucose
glucose
|
maltose
Lactose
18
Glucose and Fructose
Glucose
19
Polysaccharides
• Polymers of sugars
– costs little energy to build
• Function:
– energy storage
• starch (plants)
• glycogen (animals)
–in liver & muscles
– structure
• cellulose (plants)
• chitin (arthropods & fungi)
Polysaccharides
• Polymers of sugars joined by glycosidic linkages.
• Serve two main functions
– Storage- glycosidic linkages are hydrolyzed to obtain
monosaccharides as energy is needed.
– Structural- make up the materials that are used to
protect the organism.
Glycosidic Bonds
• Chemical linkage between the monosaccharide
units of disaccharides, and polysaccharides,
which is formed by the removal of a molecule of
water
– Condensation reaction
• Bond forms between the carbon-1 on one sugar
and the carbon-4 on the other.
Α & β Glycosidic Bonds
• An α-glycosidic bond- formed when the –OH group on
carbon-1 is below the plane of the glucose ring
• A β-glycosidic bond is formed when it is above the plane.
– Ex. Cellulose- formed of glucose molecules linked by 1-4
β-glycosidic bonds (Above plane)
– Ex. Starch- composed of 1-4 α-glycosidic bonds (Below
plane )
in cellulose
in starch
Polysaccharides- 100’s to 1000’s of
monosaccharides
Storage Polysaccharides
Structural Polysaccharides
Starch
Plants
Cellulose
Plants
Glycogen
Animals
Chitin
Animals-Insects
Fungi
24
Structural Polysaccharides
• Key in forming the structure of an organism.
• Most common structural polysaccharide is cellulose.
– Makes up cell walls in plants
– Used to make paper
• Chitin
• Polymer of glucose
• Forms via 1-4 glycosidic linkage.
Cellulose
• Most abundant organic
compound on Earth
– herbivores have evolved a mechanism to digest
cellulose
– most carnivores have not
• cellulose = undigestible roughage
But it tastes
like hay!
Who can live
on this stuff?!
Cow
can digest cellulose well;
no need to eat other sugars
Gorilla
can’t digest cellulose well; must
add another sugar source, like
fruit to diet
Helpful bacteria
• How can herbivores digest cellulose so well?
– BACTERIA live in their digestive systems & help digest
cellulose-rich (grass) meals
Rumen-Upper part of stomach
Digesting starch vs. cellulose
starch
easy to
digest
enzyme
cellulose
hard to
digest
enzyme
Plant Storage Polysaccharides
• Starch is the main storage polysaccharide- Found
in two forms.
– Amylose- main storage polysaccharide found in plants.
– 1-4 glycosidic linkage found in glucose.
– Amylopectin- also in plants.
– Like starch with branching.
– Branch occurs with a 1-6 glycosidic link.
Storage Polysaccharide in Animals
• Glycogen is the main storage polysaccharide in
animals.
• It is even more highly branched than amylopectin.
• Stored primarily in muscle and liver cells and is
used when glucose stores are low.
Polysaccharide diversity
• Molecular structure determines function
in starch
in cellulose
isomers of glucose
 structure determines function…

Linear vs. branched polysaccharides
slow release
starch
(plant)
energy
storage
glycogen
(animal)
fast release
Fig. 5-6
Chloroplast
Mitochondria
Starch
Glycogen granules
0.5 µm
1 µm
Glycogen
Amylose
Amylopectin
Starch
Unbranched
Glycogen
Branched
Difference between starch and cellulose
• Starch production involves 1-4 glycosidic
linkage of a-glucose monomers.
– Helical shape
• Cellulose production involves 1-4 glycosidic
linkage of b-glucose monomers
– Never branched , straight
• a- Glycogen
• b- Cellulose
• Does this matter?
Fig. 5-7a
a Glucose
(a) a and b glucose ring structures
b Glucose
Fig. 5-7bc
(b) Starch: 1–4 linkage of a glucose monomers
(c) Cellulose: 1–4 linkage of b glucose monomers
Chitin
• Chitin is the structural polysaccharide in arthropods
– Ex. insects, spiders, crustaceans, and fungi.
• Similar to cellulose, but it has a slightly different
monomer that is a derivative of glucose
Fig. 5-10
(a) The structure
of the chitin
monomer.
(b) Chitin forms the
exoskeleton of
arthropods.
(c) Chitin is used to make
a strong and flexible
surgical thread.
YES, It matters!
• Cellulose has a much different structure than starch.
• In storage polysaccharides, the polymer hydrogen bonds
mainly with itself to form helices (spirals)
– Ex. Glycogen
• In structural polysaccharides, the polymer hydrogen bonds
with other polymer strands to form a strands that form
thread like structures
– Ex. Chitin & Cellulose
Starch vs. Cellulose
Helix
Sheet
41
IT REALLY MATTERS
• Animals lack the enzymes (cellular machinery)
to break down cellulose.
• Only a few bacteria and fungi can break down
cellulose.