BIOLOGICAL MOLECULES
Biological molecules are macromolecules, which basically means
they are polymers composed on small repeating units that have
been covalently bonded together. The exception to this is a type
of lipid called triacyleglycerides or phospholipids which are
relatively large molecules composed of smaller molecules bonded
together.
Recall:
Macromolecule Subunit
Carbohydrate
monosaccharide
Triglyceride
fatty acids and
glycerol
Protein
amino acid
Nucleic Acid
nucleotides
Subunits are chemically liked together in the cell by a specific
type of chemical reaction called a condensation reaction. These
reactions are anabolic as they create larger molecules. When
cells need to break molecules down (e.g. digestion), they perform
catabolic reactions called hydrolysis.
What molecule do you think is common to a condensation
reaction and a hydrolysis reaction?
CARBOHYDRATES
 Contain carbon, hydrogen and oxygen in a 1:2:1 ratio
 Contain multiple hydroxyl groups (How does this affect
their ability to hydrogen bond?)
 Monosaccharides are simple sugars
o They can vary in their carbon chain length
o May assume a ring structure in water
 When glucose forms a ring there is a chance that
the –OH group will be either above or below the
plane of the of the ring
 Above the plane results in α-glucose
 Below the plane results in β-glucose
o They can vary in their carbonyl functional group
 Aldose – glyceraldehyde, ribose, glucose,
galactose
 Ketose – dihydroxyacetone , ribulose, fructose
 Disaccharides are dimers (two monomers linked together)
o Common disaccharides include sucrose, maltose and
lactose
o Monosaccharides liked by a glycosidic linkage.
Condensation Reaction/Dehydration Synthesis
R—OH
+
R1—OH

R—O—R1
+
H2 O
+ H2O
 Oligosaccharide – has several monosaccharides
linked together
 Polysaccharide – has several hundred to several
thousand monosaccharides linked together
 Starch(amylose), cellulose and glycogen
 Starch is made of α-glucose units
 Glycogen is also made of α-glucose units with
branching
 Cellulose is composed of β-glucose units
The structure of cellulose allows for maximum hydrogen bonding
between parallel molecules and this produces tight bundles called
microfibrils. This rigid structure is beneficial to plants and to
humans because:


Chitin is a glucose fortified with a nitrogen group giving it a very
strong structure.
Read pages 3235
LIPIDS
 hydrophobic molecules composed of C, H and O
 less –OH groups and longer hydrocarbons compared to
carbohydrates therefore less soluble in H2O
 suited to their function of long term stored energy reserve
and membrane components (barriers to water based cellular
environment)
 four classes
o fats
o steroids
o phospholipids
o waxes
FATS
 common energy storage in animals within adipose tissue
 thermal insulation effect
 stored as triglycerides in plants and animals
o glycerol + 3 fatty acids
O
HO—C—CH2—CH2—CH3
O
HO—C—CH2—CH2—CH==CH—CH3
O
HO—C—CH2—CH2—CH3
Fatty acids can be either saturated
(full number of hydrogen/no double bonds) or unsaturated
(contain double bonds)
A condensation reaction occurs between the carboxyl group of
the fatty acids and the hydroxyl groups of the glycerol (that’s
why you need 3 fatty acids because there are 3 hydroxyl groups).
The resulting bond is called an ester bond.
O
O
R—OH
+
R1—C—OH
 R—O—C—R1
+
H2 O
The ester bond has limited hydrogen bonding capacity. In fact,
fatty acids are stabilized by hydrophobic interactions. In a
saturated fat the hydrophobic interactions are stronger because
the fatty acid chains are able to stack very closely together, thus
forming fats that are solids at room temperature. Unsaturated
fats are liquids at room temperature because the double bonds in
the chain allow for kinking in the chain which prevents close
stacking of the molecules.
PHOSPHOLIPIDS
Phospholipids have a phosphate group on one of the carbons and
only 2 fatty acids attached via an ester linkage. The presence of
the phosphate group creates a hydrophilic end in this molecule
and the fatty acid portion is hydrophobic. This makes the
phospholipids excellent barriers as in membrane structure.
Figure 1. A Phosphlipid.
STEROIDS
 compact hydrophobic molecules containing four fused rings
and various functional groups
 cells use steroids as a building block for certain vitamins
like vitamin D
 some sex hormones are steroids
 cholesterol is an important membrane steroid that controls
cell fluidity and permeability
WAXES
 hydrophobic molecules composed on long chain fatty acids
linked to alcohols
 length of chain provides for pliable yet firm consistency
 form waterproof layers on plants
Read pgs. 1827