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Ch. 4- Carbon and the Molecular
Diversity of Life Structure and
Ch. 5- Function of
Macromolecules
A. P. Biology
Chapters 4 and 5
Mr. Knowles
Liberty Senior High School
The Uniqueness of Carbon
• Requires 4 electrons to fill its outer shell.
• Will form tetrahedral molecules with other
atoms. Has equidistant bond angles of
109.5°.
• Will readily form single, double and triple
covalent bonds.
• Carbon forms a variety of chained and
ringed organic compounds.
• Carbon is the backbone for many organic
compounds.
Carbon in a Tetrahedron!
Hydrocarbons:
– Are molecules consisting of only carbon
and hydrogen.
– Are found in many of a cell’s organic
molecules.
Fat droplets (stained red)
100 µm
Figure 4.6 A, B
(a) A fat molecule
(b) Mammalian adipose cells
Functional groups are the parts of
molecules involved in chemical
reactions
Functional groups
– Are the chemically reactive groups of atoms
within an organic molecule.
Six functional groups are
important in the chemistry of life
–Hydroxyl
–Carbonyl
–Carboxyl
–Amino
–Sulfhydryl
–Phosphate
Some important functional groups
of organic compounds
FUNCTIONAL
GROUP
HYDROXYL
CARBONYL
CARBOXYL
O
OH
(may be written HO
C
C
OH
)
STRUCTURE In a hydroxyl group (—OH),
a hydrogen atom is bonded
to an oxygen atom, which in
turn is bonded to the carbon
skeleton of the organic
molecule. (Do not confuse
this functional group with the
hydroxide ion, OH–.)
Figure 4.10
O
The carbonyl group
( CO) consists of a
carbon atom joined to
an oxygen atom by a
double bond.

When an oxygen atom is doublebonded to a carbon atom that is
also bonded to a hydroxyl group,
the entire assembly of atoms is
called a carboxyl group (—
COOH).
Some important functional
groups of organic compounds
NAME OF
COMPOUNDS
Alcohols (their specific
names usually end in -ol)
EXAMPLE
H
H
H
C
C
H
H
Ketones if the carbonyl group is Carboxylic acids, or organic
within a carbon skeleton
acids
Aldehydes if the carbonyl group
is at the end of the carbon
skeleton
H
OH
H
C
H
C
H
H
Ethanol, the alcohol
present in alcoholic
beverages
H
O
C
H
C
OH
H
H
Acetone, the simplest ketone
H
Figure 4.10
C
O
H
H
C
C
H
H
O
C
Propanal, an aldehyde
H
Acetic acid, which gives vinegar
its sour taste
Some important functional
groups of organic compounds
FUNCTIONAL  Is polar as a result of the
PROPERTIES electronegative oxygen atom
drawing electrons toward
itself.
 Attracts water molecules,
helping dissolve organic
compounds such as sugars
(see Figure 5.3).
 A ketone and an
aldehyde may be
structural isomers with
different properties, as
is the case for acetone
and propanal.
 Has acidic properties because
it is a source of hydrogen ions.
The covalent bond between
oxygen and hydrogen is so polar
that hydrogen ions (H+) tend to
dissociate reversibly; for
example,
H
H
C
H
Figure
4.10
H
O
C
OH
H
C
H
O
+ H+
C
O
 In cells, found in the ionic
form, which is called a
carboxylate group.
Some important functional
groups of organic compounds
AMINO
SULFHYDRYL
H
N
H
Figure 4.10
O
SH
(may be written HS
The amino group (—NH2)
consists of a nitrogen atom
bonded to two hydrogen
atoms and to the carbon
skeleton.
PHOSPHATE
)
O P OH
OH
The sulfhydryl group
consists of a sulfur atom
bonded to an atom of
hydrogen; resembles a
hydroxyl group in shape.
In a phosphate group, a
phosphorus atom is bonded to four
oxygen atoms; one oxygen is
bonded to the carbon skeleton; two
oxygens carry negative charges;
abbreviated P . The phosphate
group (—OPO32–) is an ionized
form of a phosphoric acid group (—
OPO3H2; note the two hydrogens).
Some important functional
groups of organic compounds
H
O
C
HO
C
OH
OH
N
OH
Glycine
Figure 4.10
OH
OH
OH
C
C
OH
OH
OH OH OH
SH
OH
C
C
C
OH OH O H
O
O
P
O
O
Ethanethiol
Because it also has a carboxyl
group, glycine is both an amine
and a carboxylic acid;
compounds with both groups
are called amino acids.
Glycerol phosphate
Some important functional
groups of organic compounds
 Two sulfhydryl groups can
 Acts as a base; can pick
interact to help stabilize
protein structure (see
Figure 5.20).
up a proton from the
surrounding solution:
H
N
H
+N
H
(nonionized)
H
(ionized)
 Ionized, with a charge
Figure 4.10
of 1+, under cellular
conditions.
H
 Makes the molecule of which
it is a part an anion (negatively
charged ion).
Can transfer energy between
organic molecules.
Functional groups give organic
molecules distinctive chemical
properties
Estradiol
CH3
OH
HO
Female lion
CH3
OH
CH3
O
Figure 4.9
Male lion
Testosterone
Organic Compounds
• Four major groups:
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic Acids
• Differ in their functional groups;
Fig. 3.2, p.45.
Organic Compounds
• Some organic compounds are small
with one or a few functional groupsmonomers. (Ex. Glucose =
monosaccharide).
• Other organic compounds are made
from linking several simple
monomers together in complex
chains- polymers (1000’s of glucose
monomers = starch, polysaccharide).
Monomers

Polymers
Simple
Complex
• Monosaccharides 
Polysaccharides
• Glycerol, Fatty Acids Lipids, Fats
• Amino Acids 
Proteins
• Nucleotides 
Nucleic Acids
Building Macromolecules
• All polymers are formed by
making covalent bonds between
two monomers.
• The –OH group from one
monomer is removed and the –H
from the other is removed –
Dehydration Synthesis
• H2O is removed which requires
energy.
Dehydration Synthesis
HO
H
ENERGY
HO
HO
H
HOH
H
Dehydration Synthesis
• When polymers are built from smaller
monomers- anabolic reactions
(synthesizing). Requires energy.
• These reactions require the reactants
to be held close together and chemical
bonds to be stressed and brokencatalysis.
• Catalysis is caused by enzymes.
Hydrolysis Reactions
• Cells may also disassemble polymers into
monomers- catabolic reactions
(breakdown).
• A molecule of H2O is added and split; a H
is added to one monomer and the OH is
added to the other-hydrolysis (water
splitting).
• Catabolic reactions release the energy
stored in the bonds of the monomers.
Carbohydrates
• Contain C, H, O atoms (CH2O)n
• Functions:
Main source of energy- for
immediate use or for energy storage,
Used for structure- on surfaces of
cell membranes (bacteria,
eukaryotes), or support cell walls
(plants).
Three Types of Carbohydrates
1. Monosaccharides- “mono”single; simple sugars that are
made of 3-6 C’s in a chain or
ring.
Ex. C6H12O6 , Glucose, most
abundant monosaccharide
Straight Chain or Rings
Monosaccharides- Isomers
Three types of isomers are:
– Structural
– Geometric
– Enantiomers
(a) Structural isomers
H
H
H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
X
(b) Geometric isomers
H
H
C
H
C
NH2
CH3
Figure 4.7 A-C
X
CO2H
C
H
H
X
H
CO2H
c) Enantiomers
H
C
C
C
H
C
H
H
H
C
C
H
X
C
H
H
H
C
H
H
NH2
CH3
H
Enantiomers:
Are important in the pharmaceutical
industry.
Figure 4.8
L-Dopa
D-Dopa
(effective against
Parkinson’s disease)
(biologically
inactive)
Isomers
Structural Isomersmonosaccharides with the
same empirical formula
but different structures.
Ex. Glucose and Fructose
Isomers
• Stereoisomers –
monosaccharides that have the
same empirical formula but they
have functional groups as mirror
images of each other.
• Ex. Glucose and Galactose
Monosaccharides of Nucleic
Acids
Other Monosaccharides
• Fructose- commonly found
in fruit.
• Galactose- found in milk.
• Ribose- found in RNA.
• Deoxyribose- found in DNA.
Monosaccharides
• Most offer a number C-H bonds
as potential chemical energy.
• May also be used as monomers
to build more complex polymers
for energy storage or structural
molecules.
2. Disaccharides
• Are two monosaccharides that
form a glycosidic bond by
removing a H2O molecule.
• Glucose + Fructose-->Sucrose
(table sugar)
Sucrose- A Disaccharide
(Umm!)
Disaccharides
• Monosaccharides (glucose) is often
converted into a disaccharide before
being transported around an
organism’s body.
• Unable to be used in this form until
it arrives at a tissue.
• Plants transport glucose as sucrose.
(sugar cane)
Lactose (MOO!)
Lactose
• Mammals use lactose to
transport glucose to infant.
• Adults usually lack the
enzyme, lactase, which breaks
down lactose glucose +
galactose.
Other Disaccharides
• Sucrose (Table Sugar)- Glucose +
Fructose
• Lactose (Milk Sugar)- Glucose +
Galactose
• Maltose (Breakdown from Starch)Glucose + Glucose
3. Polysaccharides
• Formed when monosaccharides are
linked in chains by glycosidic
bonds.
• They are polymers- long chains of
monomers (building blocks).
• Polymer = polysaccharide,
• Monomers = monsaccharides
Polysaccharides
• Two Basic Functions1. Storage Polysaccharides:
May store 1000’s of monomers
for energy. Usually stored in
special storage structures.
2. Structural: May form
structural parts of cells and/or
tissues.
Starch = Amylose
Chloroplast
Starch
1 m
Amylose
Figure 5.6
Amylopectin
(a) Starch: a plant polysaccharide
Plant Storage- Starch
• Amylose- hundreds of glucose molecules
in a long, unbranched chain.
• The glycosidic bond is between the 1C4C.
• The chains coil in water and don’t form H
bonds, therefore not very soluble in H2O.
• Only 20% of starch in potatoes is amylose.
• 80% is amylopectin- short and branched
glucose chains. Is cross-linked.
Starch Storage
• Plants use special tissues
called tubers.
• Also stored in bulbs of
perennials.
Glycogen:
– Consists of glucose monomers.
– Is the major storage form of glucose in
animals.
Mitochondria
Giycogen granules
0.5 m
Glycogen
Figure 5.6
(b) Glycogen: an animal polysaccharide
Animal Storage- Glycogen
• Insoluble, branched amylose
chains.
• Longer and more branched than
starch.
• Stored in liver and skeletal
muscle.
• Not transported in blood.
Starch
Cellulose
Cellulose has different glycosidic linkages than
starch.
H
O
C
CH2OH
H
4
O
H
OH
H
HO
C
H
H
C
OH
H
C
OH
H
C
OH
OH
HO
OH
H
OH
C
H
H
CH2OH
 glucose
H
O
H
OH
4
OH
1
H
HO
H
H
OH
 glucose
(a)  and  glucose ring structures
HO
CH2OH
CH2OH
CH2OH
CH2OH
O
O
O
O
4
1
OH
O
1
OH
4
O
OH
OH
1
OH
4
O
1
OH
O
OH
OH
(b) Starch: 1– 4 linkage of  glucose monomers
OH
CH2OH
O
HO
O
OH
1
OH
O
O
OH
CH2OH
OH
O
O
OH
Figure 5.7 A–C
4
OH
CH2OH
O
OH
(c) Cellulose: 1– 4 linkage of  glucose monomers
CH2OH
OH
Structural Polysaccharides
• Cellulose- a chain of glucose molecules
in which the monomers alternate
positions.
• Similar to amylose but not recognized
by the same enzymes. Resistant.
Compare in Fig. 3.7.
• A water-tight, structural molecule.
• Plant cell walls
Cellulose- A Structural
Polysaccharide of Plants
A major component of the tough walls that
enclose plant cells
Cellulose microfibrils
in a plant cell wall
Cell walls
Microfibril
About 80 cellulose
molecules associate
to form a microfibril, the
main architectural unit
of the plant cell wall.
0.5 m
Plant cells
Parallel cellulose molecules are
held together by hydrogen
bonds between hydroxyl
groups attached to carbon
atoms 3 and 6.
Figure 5.8
OH CH2OH
OH
CH2OH
O O
O O
OH
OH
OH
OH
O
O O
O O
O CH OH
OH
CH2OH
2
H
CH2OH
OH CH2OH
OH
O O
O O
OH
OH
OH
OH
O
O
O O
O
O CH OH
OH CH2OH
2
H
CH2OH
OH
OH CH2OH
O O
O O
OH
OH
OH
OH O
O
O O
O
O CH OH
OH
CH2OH
2
H
 Glucose
monomer
Cellulose
molecules
A cellulose molecule
is an unbranched 
glucose polymer.
• Cellulose is difficult to digest:
– Cows have microbes in their stomachs to
facilitate this process (relationship?).
Figure 5.9
Termite Colony
Koalas and Eucalyptus
I have
indigestion!
Polysaccharides and Clean
Hair!
Chitin
• 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
(a) The structure of the
chitin monomer.
Figure 5.10 A–C
(b) Chitin forms the exoskeleton
of arthropods. This cicada
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.
3. Chitin
• Structural polysaccharide of Arthropods
(insects and crustaceans) and fungi.
• Modified form of cellulose; has an added
nitrogen group to each glucose unit.
• Hard, flexible, and water-tight.
• Few organisms can digest.
• Exoskeleton of Arthropods.
My Kind of Polysaccharide!
Biology Lab Manual, Lab
#3, pp.29-31
Testing for
Carbohydrates
Reactive Groups in
Monosaccharides
Groups are Missing in Sucrose
The Benedict’s Test
Cu 2+ (Cupric Ions)
Heat and High pH
H
Reducing Sugar
Cu+ (Cuprous Ions)
H
Cu (Most Reduced Copper)
Benedict’s Test for Reducing
Sugars
+
-
?
Positive and Negative Control
for Starch