Course code: G109

Biological Macromolecules
 The FOUR Classes of Large Biomolecules

• All living things are made up of four classes of

large biological molecules:
• Carbohydrates
• Lipids
• Protein
• Nucleic Acids

• Macromolecules are large molecules composed

of thousands of covalently bonded atoms

• Molecular structure and function are inseparable

 The FOUR Classes of Large Biomolecules

• Macromolecules are polymers, built

from monomers
• A polymer is a long molecule consisting of many
similar building blocks.
• These small building-block molecules are called
monomers.
• Three of the four classes of life’s organic
molecules are polymers
– Carbohydrates
– Proteins
– Nucleic acids
 The Diversity of Polymers

• Each cell has thousands of different macromolecules.

• Macromolecules vary among cells of an organism,

vary more within a species, and vary even more
between species.

• An immense variety of polymers can be built from a

small set of monomers.
 Components of Life

Data from E. coli:

Component % by weight Complexity*

Water 70 1
Protein 15 3000
Nucleic Acids 7 1001
Carbohydrate 3 50
Lipids 2 40
Smallorganics 2 500
Inorganics 1 12

*number of types
6
 Carbohydrates: serve as Fuel
and Building Material

• Carbohydrates include sugars and the polymers

of sugars

• The simplest carbohydrates are

monosaccharides, or single sugars

• Carbohydrate macromolecules are

polysaccharides, polymers composed of many
sugar building blocks
 How are Carbohydrates classified?
• On their behavior towards hydrolysis, they
are divided into:
 Monosaccharides - simple sugars with multiple OH groups.
Based on number of carbons (3, 4, 5, 6), a
monosaccharide is a triose, tetrose, pentose or hexose.
 Disaccharides - 2 monosaccharides covalently linked.
 Oligosaccharides - a few monosaccharides covalently
linked.
 Polysaccharides - polymers consisting of chains of
monosaccharide or disaccharide units.
 Sugars: Monosaccharides

• Monosaccharides have molecular Glucose

formulas that are usually multiples
of CH2O

• Glucose (C6H12O6) is the most

common monosaccharide

• Monosaccharides are classified by

Main “fuel” for
– The location of the carbonyl group
bacteria, plants
– The number of carbons in the and animal cells
carbon skeleton
 Sugars: Disaccharides
• A disaccharide is formed when a dehydration
reaction joins two monosaccharides

• This covalent bond is called a glycosidic linkage

 Functions of Disaccharides

 Sucrose, for example, is table sugar, and it is the

most common disaccharide that humans eat.
Glucose and Fructose

 Lactose is found in breast milk and provides

nutrition for infants. Glucose and Galactose

 Maltose is a sweetener that is often found in

chocolates and other candies. Glucose and
Glucose

 Since it is an energy storage source, many plants

such as sugar cane are high in sucrose.
 Polysaccharides

• Polysaccharides, the polymers of sugars, have storage

and structural roles
• The structure and function of a polysaccharide are
determined by its sugar monomers and the positions of
glycosidic linkages
 Types of Polysaccharides: Storage

• Starch, a storage
polysaccharide of
plants, consists
entirely of glucose
monomers
• Plants store surplus
starch as granules
within chloroplasts
and other plastids
• The simplest form of
starch is amylose
 Types of Polysaccharides: Storage

• Glycogen is a
storage
polysaccharide in
animals
• Humans and other
vertebrates store
glycogen mainly in
liver and muscle cells
Types of Polysaccharides: Structural

• The polysaccharide cellulose is a major

component of the tough wall of plant cells
• Like starch, cellulose is a polymer of glucose, but
the glycosidic linkages differ
• The difference is based on two ring forms for
glucose: alpha () and beta ()
Such Elegance!
 Polysaccharide
Random Acts of Biology
• Cellulose in human food passes through the
digestive tract as insoluble fiber
• Some microbes use enzymes to digest cellulose
• Many herbivores, from cows to termites, have
symbiotic relationships with these microbes

• Chitin, another structural polysaccharide, is found

in the exoskeleton of arthropods (crunch!)

• Chitin also provides structural support for the cell

walls of many fungi
 Who knew?

Chitin Shell
Amino acid and Protein
Proteins are polymers of amino acids.
This is an amino acid. It
is the monomer for a
protein. It contains C, H,
O and N. It has 3 groups:
an amino group, an R-
group, and a carboxyl
group. The R-group is
considered a variant
group because it
changes.
Natural Amino acids (20 types)
 Proteins
 Elements: C-H-O-N
 Monomer (Building Block):
amino acids (20 different
ones!)
 Polymer: proteins (tons)
 Examples of proteins:
hemoglobin in red blood cells,
albumin in eggs, enzymes that
control reactions in the body,
and antibodies
 Found in: fish, eggs, meat
What are the forces between amino acid residues
in a protein?

Ionic interactions between oppositely charged residues

can pull them together.
Hydrogen Bonds - Hydrogens are partially positively
charged, are attracted to partially negative oxygens.
(weaker)
van Der Waals - hydrophobic residues become attractive to
each other when forced together by exclusion from the
aqueous surroundings. (weakest)
Examples of interactions contributing to the tertiary
structure of a protein
Function of Proteins
• Provides us with building
blocks for life.
• Also regulate most functions
in a cell.
• Combines with DNA to form
chromosomes
• Antibodies (fights disease)
 Function of
Proteins
 Provides structure & strength
(fibers)
 Transports molecules in & out
cells
 Hemoglobin (transports O2)
 Enzymes (speeds up
reactions)- i.e. Amylase
 Acts as hormones. i.e. insulin
Lipids and Fats
 Lipids are Hydrophobic
Lipids are a diverse group of hydrophobic
molecules
• Lipids are the one class of large biological
molecules that do not form polymers
• The unifying feature of lipids is having little or no
affinity for water (water fearing)
• Lipids are hydrophobic because they consist
mostly of hydrocarbons, which form nonpolar
covalent bonds
• The most biologically important lipids are fats,
phospholipids, and steroids
 Fats: Start with a Simple
Glycerol Molecule

• Fats are constructed from two

types of smaller molecules:
glycerol and fatty acids
• Glycerol is a three-carbon alcohol
with a hydroxyl group attached to
each carbon
• A fatty acid consists of a carboxyl
group attached to a long carbon
skeleton
Dehydration Reaction 1: Add a Fatty Acid

• Next, add a “fatty acid” through a dehydration

synthesis reaction
 Dehydration Reaction 2!!

• Next, add a SECOND “fatty acid” through a

dehydration synthesis reaction
 Dehydration Reaction THREE!!!

• The joining of
the C of the
fatty acid to
the O of the
hydroxyl
group of the
glycerol is
called an
ester linkage.
 Saturated or Unsaturated?
• Fats made from
saturated fatty acids
are called saturated
fats, and are solid at
room temperature
• Most animal fats are
saturated (lard)
• Saturated fatty acids
have the maximum
number of hydrogen
atoms possible and no
double bonds
 Saturated or Unsaturated?
• Fats made from
unsaturated fatty acids are
called unsaturated fats or
oils, and are liquid at room
temperature
• Plant fats and fish fats are
usually unsaturated
• Unsaturated fatty acids
have one or more double
bonds
 Saturated or Unsaturated?
• A diet rich in saturated
fats may contribute to
cardiovascular disease
through plaque deposits

• Hydrogenation is the
process of converting
unsaturated fats to
saturated fats by adding
hydrogen
 What’s a Trans fat?

• Hydrogenating vegetable oils also creates

unsaturated fats with trans double bonds
• These trans fats may contribute more than
saturated fats to cardiovascular disease
 Saturated or Unsaturated?

• Certain unsaturated fatty acids are not synthesized

in the human body
• These must be supplied in the diet
• These essential fatty acids include the omega-3 (ω-
3) fatty acids, required for normal growth, and
thought to provide protection against cardiovascular
disease
 Fats: Major function is storage!

• The major function of

fats is energy storage
• Humans and other
mammals store their
fat in adipose cells
• Adipose tissue also
cushions vital organs
and insulates the
body
 Phospholipids
• When phospholipids are added to water, they self-
assemble into a bilayer, with the hydrophobic tails
pointing toward the interior
• The structure of phospholipids results in a bilayer
arrangement found in cell membranes
• Phospholipids are the major component of all cell
membranes
Carbohydrate
Phospholipid
bilayer

Nonpolar
Hydrophobic
Polar
Hydrophilic
 A Single Phospholipid Molecule

Choline
Hydrophilic head

Phosphate

Glycerol
Hydrophobic tails

Fatty acids

Hydrophilic
head

Hydrophobic
tails

(a) Structural formula (b) Space-filling model (c) Phospholipid symbol

 Soaps
Hydrophobic part: nonpolar

Hydrophilic part: polar (remains in contact with environment)

O
- +
3 RCO N a

l Sodium soaps
n)
 Soaps
When soap is mixed with dirt (grease, oil, and …), soap
micelles “dissolve” these nonpolar, water-insoluble
molecules.
 Steroids
• Steroids are lipids characterized by a carbon
skeleton consisting of four fused rings
• Cholesterol, an important steroid, is a component
in animal cell membranes
• Although cholesterol is essential in animals, high
levels in the blood may contribute to
cardiovascular disease
 Sex Hormones
Progestins (Female Sex Hormones):

The progestin progesterone is called the “pregnancy

hormone”; it is responsible for the preparation of the uterus for
implantation of a fertilized egg.
 Sex Hormones
Androgens (Male Sex Hormones):

Testosterone and Androsterone are androgens made in the

testes.
They control the development of secondary sex
characteristics in males.
 Sex Hormones
- Synthetic androgen analogues, called anabolic steroids,
promote muscle growth.
- They have the same effect as testosterone, but are more
stable, so they are not metabolized as quickly.

- They have come to be used by athletes and body builders,

but are not permitted in competitive sports.
- Prolonged use of anabolic steroids can cause physical and
psychological problems.
Next Lecture:
Information Molecules and Central
Dogma of Molecular Biology