Biology 102
Lecture 4: Biological Molecules
Lecture outline
1. Organic molecules: Overview
2. Carbohydrates
 Functions
 Structure
3. Lipids
1. Living organisms are
composed of organic molecules

Organic: Have a carbon “skeleton”
Carbon-carbon
bonds
Each C atom can form as many as 4 bonds
with other atoms
 What other molecule is similar?

Functional groups
Specific
arrangements of atoms that give
each type of organic molecule their unique
characteristics

All organisms are composed of similar
organic molecules
 Carbohydrates
 Lipids
 Proteins
 Nucleic

acids
Complex biological molecules
(polymers) are synthesized from more
simple molecules (monomers)
 So,
monomers are basically subunits of polymers.

Biological molecules are joined together by
removing water: Dehydration synthesis
Audesirk, p. 39

Biological molecules are split apart by adding
water: Hydrolysis
 “hydro”=water,
“lysis”=to cut
Audesirk, p. 39
2. Carbohydrates

Key functions:
Serve


as a source of energy
Energy is “stored” within the bonds of all organic
molecules, but carbohydrates are the most easily
broken down to release energy
Starch, glycogen and glucose are all examples of
carbohydrates that provide energy
Provide


structure
Cellulose forms the cell walls of plants
Chitin forms the cell walls of fungi and the
exoskeleton of arthropods (insects, crabs, etc…)
Structure of carbohydrate monomers

Composition




Monosaccharides: sugar
monomer, or “single
sugar”
When dissolved in water,
usually forms a ring


Contain Carbon, Hydrogen
and Oxygen at ratios of 1:2:1
So, literally is Carbon plus
water!
Here, ring is 5 carbons and
one o the oxgyens
Carbohydrates are polar

Where are the negative and
positive charges?
C6H12O6
Several other monosaccharides with
slightly different structures from glucose




Fructose: sugar found in
corn syrup and orange
juice
Galactose: sugar found in
milk
Ribose: sugar that forms
part of RNA backbone
Deoxyribose: sugar that
forms part of DNA
backbone
Carbohydrate polymers

Disaccharides: “di” means “two”
Two
monosaccharides linked by
dehydration synthesis
Note how an “H” of one monosaccharide
combines with the “OH” of the other.
Audesirk,
Fig. 3-1
Polysaccharides are chains of monosaccharides

Starch: energy storage


Cellulose: structure



Enzyme in our saliva
breaks down starch into
sugar monomers
Forms plant cell walls
We cannot break down
cellulose, so it passes
undigested through us
Chitin: structure


Cell walls of fungi
Contains nitrogen atoms!
3. Lipids

Key functions
 Energy

storage molecules (i.e. fat); long-term
Fats and oils have over 2X the amount of energy for a given
unit of weight compared to carbohydrates:

9.3 Calories/g compared to 4.1 Calories/g
 Waterproof
coverings on plants and animals
 Essential components of cell membranes
 Hormones (i.e. testosterone and estrogen)

Contain large non-polar regions
 Specifically,
polar
the long hydrocarbon chains are non-
Oils and fats (triglycerides)


Contain only Carbon, Hydrogen and Oxygen
(just like carbohydrates!)
Formed when three fatty acid subunits join to
a single glycerol molecule
 Synthesized
with a dehydration synthesis reaction
The difference between oils and fats

Fats: solid at room temperature
They
are “saturated” with Hydrogens: NO
DOUBLE BONDS BETWEEN CARBONS


Resulting hydrocarbon chain is straight
Allows chains to fit together in solid clumps
HHHHHH
-C-C-C-C-C-C-H
HHHHHH
The difference between oils and fats
(cont.)

Oils: liquid at room temperature
They
are “unsaturated” : HAVE SOME
BONDS BETWEEN CARBONS


Resulting hydrocarbon chain is kinked
Do not fit together as well, and so remain fluid
HH
HHH
-C-C=C-C-C-C-H
H
HHHH
Note the double bond and
lower number of Hydrogens:
“unsaturated”
Phospholipids

Key component of membranes,
including the plasma (cell) membrane
Phosphate-containing

Note where the charges would be…
Two

head region (polar!)
fatty acid tails (non-polar)
Why not polar?
Steroids


Composed of four rings of carbon
Various functional groups protrude from the
rings
Cholesterol:
•Key component of
membranes
•Used to synthesize other
steroids
Testosterone and
estradiol
•Sex hormones
•Note similarity in structure