Complex Structures and
Functions of Carbohydrates
• Monosaccharides- single sugars
– Glucose C6H12O6
– Fructose
•Disaccharides- double sugars
–Sucrose ( table sugar)
•Polysaccharides- three or more
monosaccharides
–Macromolecule
–Starch
–Glycogen
–Cellulose- provides structure for
plants (humans cannot digest)
Glucose and other monosaccharides often form ring structures
#5
#1
The ring forms when a hydrogen is transferred from the
hydroxyl group on the #5 carbon to the oxygen of the
carbonyl group on the #1 carbon.
This allows the #1 carbon to form a bond with the oxygen
attached to the #5 carbon, completing the ring.
Give an example of a monosaccharide.
Give an example of a disaccharide.
Give an example of a polysaccharide.
What is the molecular formula for this
sugar, and how do you know it is a sugar?
Two [or more] monosaccharides may be joined by dehydration
synthesis to produce larger disaccharides and polysaccharides.
Dehydration means to take water out. When dehydration
synthesis occurs, something is being built, while taking
water out, or producing water as a product.
XOH + HZ  XZ + HOH
Dehydration synthesis is a typical condensation reaction.
The reverse reaction of breaking up polymers is
accomplished by another chemical reaction known as
hydrolysis.
Hydrolysis is simply the reverse of dehydration synthesis. You add water to a
molecule to break it down.
X + H2O --> HX + OH
Glucose is a very common monosaccharide that is used for cellular
respiration among other things. The names of most sugars end in –ose. The
carbon skeletons of monosaccharides are usually 3-7 carbon atoms long.
Glucose and fructose are hexoses (six-carbons long), pentoses have five
carbons, and trioses have three carbons.
Two glucose molecules can be joined to produce a molecule of
maltose [and a molecule of water].
A glycosidic link
occurs when two
monosaccharides
are joined by
dehydration
synthesis.
A second disaccharide, the common table sugar known as
sucrose, is produced by combining glucose and fructose.
If dehydration synthesis continues for a long time, a long and
complex carbohydrate chain called a polysaccharide is formed.
Polysaccharides are produced by adding more monosaccharides
to the chain. Some of the most important polysaccharides are
made of long polymers of glucose.
What element can be found at each corner in the ring?
In glycogen, or animal starch, the glucose units are again
joined to produce long chains, but side chains are linked to the
main chain.
What process joins two monosaccharides together?
What type of reaction is dehydration synthesis?
When two monosaccharides are joined together, what are the
products?
What reaction breaks down polysaccharides?
What are the reactants in hydrolysis?
Where does a glycosidic link form?
Storage Polysaccharides
Chloroplast
Starch
• Starch
– Is a polymer
consisting
entirely of
glucose
monomers
– Is the major
storage form of
glucose in plants
1 m
Amylose
Amylopectin
Plastids are organelles such
as chloroplasts, which store
starch.
Glycogen is the storage form of glucose in animals and humans
which is analogous to the starch in plants. Glycogen is
synthesized and stored mainly in the liver and the muscles
Plants make glucose and cellulose
through the photosynthesis
processes, and store starch
primarily in their roots.
Animals in turn eat plant
materials and products.
Digestion is a form of hydrolysis where
the starch is broken down into the
various monosaccharides. A major
product is glucose, which can be used
immediately for metabolism to make
energy, through the process of cellular
respiration.
Mitochondria
Giycogen
granules
0.5 m
Glycogen
The glucose that is not used immediately is converted in the
liver and muscles into glycogen for storage. Any glucose in
excess of the needs for energy and storage as glycogen is
converted to fat.
Where is most starch stored in plants?
What are plastids?
What is animal starch called, and where is it produced and
stored mainly?
What process in animals can be likened to hydrolysis, and what
is the main product of hydrolysis?
What is that glucose used for?
What happens if glucose exceeds energy and storage needs?
Another polysaccharide, cellulose, has its glucose units
joined together, however, alternating glucose units are 'flipflopped'.
Changes in the bond configuration cause changes in the final
shape and function of the molecules.
Cellulose is found in plant cells,
and forms the structurally
strong framework in the cell
wall. It’s lattice-like structure
makes it very strong indeed.
• Cellulose is difficult to digest
– Cows and other herbivores have microbes in
their stomachs to facilitate this process
Humans do not!
• Chitin, another important structural
polysaccharide
– Is found in the exoskeleton of arthropods
– Can be used as surgical thread
CH2O
H
O OH
H
H
OH H
OH
H
H
NH
C
O
CH3
(b) Chitin forms the exoskeleton
(a) The structure of the
of arthropods. This cicada
chitin monomer.
is molting, shedding its old
exoskeleton and emerging
in adult form.
(c) Chitin is used to make a
strong and flexible surgical
thread that decomposes after
the wound or incision heals.
What is the structural significance of cellulose
in plants?
How do herbivores digest cellulose?
What element can be found in the
polysaccharide chitin, that isn’t in other
carbohydrates?
Fats and oils are made from two kinds of molecules:
Complex Structures and Functions of Lipids
Do you remember what fats are composed of?
• glycerol (a type of alcohol)…and three
• fatty acids joined to it by dehydration synthesis.
Since there are three fatty acids attached, these are known
as triglycerides.
The main distinction
between fats and oils is
whether they’re solid or
liquid at room temperature,
and this is based on
differences in the
structures of the fatty
acids they contain.
The “tail” of a fatty acid is a long hydrocarbon chain, making it
hydrophobic.
• Hydrophobic means fear of water…so the tail end of a fatty acid is nonpolar, and
will not associate with water at all.
The “head” of the molecule is a carboxyl group which is hydrophilic.
• Hydrophilic means water friendly…so the head end of a fatty acid will readily
associate with water.
Fatty acids are the main
component of soap, where
their tails are soluble in oily
dirt and their heads are
soluble in water to emulsify
and wash away the oily dirt.
However, when the head end is
attached to glycerol to form a
fat, that whole molecule is
Glycerol
hydrophobic.
Backbone
What process joins the fatty acids to the glycerol
to make fat?
The tail of a fatty acid is a nonpolar hydrocarbon.
What word describes its association with water?
The head end of a fatty acid has a carboxyl group
which is hydrophyllic. Describe its association
with water.
What part of the fat makes the whole molecule
hydrophobic?
• Saturated fatty acids
– straight molecules
–Generally solid at room temperature
–Butter, lard, grease from cooked meats
– Contain no double bonds between carbons
• Unsaturated fatty acids
–Some carbon atoms linked by a “double’ covalent bond
–Generally liquid at room temperature
–EX: olive oil, fish oils
•Hydrogenated vegetable oils contain naturally unsaturated
fatty acids that have been saturated artificially (with
hydrogen) and are generally solid at room temperature
–EX: margarine, vegetable shortening
How do you know the fat on this meat is a saturated fat?
How are the carbon bonds between saturated and
unsaturated fats different?
Describe how hydrogenated unsaturated fatty acids are
different from natural unsaturated fatty acids.
Phospholipids are made from
•glycerol
•two fatty acids, and (in place of the third fatty acid)
•a phosphate group with some other molecule The hydrocarbon tails of the
fatty acids are still
attached to its other end.
hydrophobic, but the
phosphate group end of the
molecule is hydrophilic
because of the oxygens with
all of their pairs of unshared
electrons.
This means that phospholipids
are soluble in both water and
oil.
This becomes especially
important as we learn about
cells, and the structure of
their membranes.
Our cell membranes are made mostly of phospholipids arranged in a double layer
with the tails of the fatty acids from both layers “inside” (facing toward each
other) and the heads facing “out” (toward the watery environment) on both
surfaces. This protects the cell from many molecules moving across the membrane.
Structure of the
Phospholipid Bilayer
+
CH2
CH2
N(CH3)3
Choline
Outside of cell
O
O
O–
P
Phosphate
O
CH2
CH
O
O
C
O C
CH2
Glycerol
O
Fatty acids
Hydrophilic
head
Hydrophobic
tails
Inside of cell
Figure 5.13
(a) Structural formula
(b) Space-filling model
(c) Phospholipid
symbol
How are phospholipids different from other lipids,
structurally?
What is the significance of the phosphate group on the
phospholipid?
Why are phospholipids important in the structure of our
cell membranes?
Cholesterol is not a “bad guy!” Our bodies make about 2 g of cholesterol per day,
and that makes up about 85% of blood cholesterol, while only about 15% comes
from dietary sources.
• Cholesterol is the precursor to our sex
hormones and
• Vitamin D
Vitamin D is formed by the action
of UV light in sunlight on
cholesterol molecules that have
“risen” to near the surface of the
skin.
Our cell membranes contain a lot
of cholesterol (in between the
phospholipids) to help keep them
“fluid” even when our cells are
exposed to cooler temperatures.
Steroids may be recognized by
their skeleton, consisting of three
fused six-membered and one fivemembered ring
Waxes are widely
distributed in nature.
The leaves and fruits
of many plants have
waxy coatings, which
may protect them
from dehydration and
small predators.
The feathers of birds and
the fur of some animals
have similar coatings which
serve as a water repellent.
Cuticle
Cuticle
Ocotillo Cacti
Lipoproteins are clusters of proteins and lipids all
tangled up together. These act as a means of carrying
lipids, including cholesterol, around in our blood.
There are two main categories of lipoproteins distinguished
by how compact/dense they are.
•LDL or low density lipoprotein is
the “bad guy,” being associated with
deposition of “cholesterol” on the
walls of someone’s arteries.
•HDL or high density lipoprotein is
the “good guy,” being associated
with carrying “cholesterol” out of
the blood system, and is more
dense/more compact than LDL.
Many plant pigments, such as anthocyanins, chlorophylls A and
B, carotenoids and xanthophylls are lipids.
Some lipid pigments can also appear in animals, like
cichlids…and people.
Xanthophylls and melanins
Which is the “bad guy”, LDL or HDL,
and why?
What lipid plays a key role in the
“fluidity” of the cell membranes?