THE MOLECULES OF LIFE
CHAPTER 3
POLYMERS ARE BUILT OF
MONOMERS
• Organic molecules are formed by living
organisms.
• Carbon-based core
• The core has attached groups of atoms called
functional groups.
• The functional groups confer specific chemical
properties on the organic molecules.
FIVE PRINCIPAL FUNCTIONAL
GROUPS
Group
Structural
Formula
Hydroxyl
Ball-andStick Model
OH
Carbonyl
C
O
O
Amino
O
H
Carbohydrates
C
O
Lipids
O
C
C
Carboxyl
Proteins
OH
O
H
H
N
Proteins
H
O–
O–
O
H
N
H
Phosphate
Found In
P
O
O–
O
P
O
O–
DNA,
ATP
MACROMOLECULES
• The building materials of the body are
known as macromolecules because they
can be very large.
• There are four types of macromolecules:
1. Proteins
2. Nucleic acids
3. Carbohydrates
4. Lipids
MACROMOLECULES
• Large macromolecules are actually
assembled from many similar small
components, called monomers.
• The assembled chain of monomers is known as a
polymer.
DEHYDRATION SYNTHESIS
• All polymers are assembled the same way.
• A covalent bond is formed by removing a
hydroxyl group (OH) from one subunit and a
hydrogen (H) from another subunit.
DEHYDRATION SYNTHESIS
• Because this amounts to the removal of a molecule
of water (H2O), this process of linking together two
subunits to form a polymer is called dehydration
synthesis.
H2 O
HO
H
H HO
Energy
HO
H
HYDROLYSIS
• The process of disassembling polymers into
component monomers is essentially the
reverse of dehydration synthesis.
• A molecule of water is added to break the
covalent bond between the monomers.
• This process is known as hydrolysis.
HO
HO
H 2O
H
Energy
HHO
H
PROTEINS
• Proteins are complex macromolecules that
are polymers of many subunits called amino
acids.
PROTEINS
• The covalent bond linking two amino acids
together is called a peptide bond.
• The assembled polymer is called a
polypeptide.
Amino acid
H
H
R
N
C
C
H
O
Amino acid
H
OH
H
R
N
C
C
H
O
H2O
Polypeptide chain
H
H
R
N
C
C
H
O
H
R
N
C
C
H
O
OH
OH
PROTEINS
• Amino acids are small molecules with a
simple basic structure, a carbon atom to
which three groups are added:
• an amino group (—NH2)
• a carboxyl group (—COOH)
• a functional group (R)
• The functional group gives amino acids their
chemical identity.
• There are 20 different types of amino
acids.
PROTEINS
• Protein structure is complex.
• The order of the amino acids that form the
polypeptide is important.
• The sequence of the amino acids affects how
the protein folds together.
PROTEINS
• The way that a polypeptide folds to form the
protein determines the protein’s function.
• Some proteins are comprised of more than one
polypeptide.
PROTEINS
Primary
structure
Amino acids
•
There are four
general levels of
protein structure:
1.
2.
3.
4.
Primary
Secondary
Tertiary
Quaternary
Secondary
structure
β-pleated sheet
α-helix
O
Tertiary
structure
Quaternary
structure
PROTEINS
• Primary structure—the sequence of amino
acids in the polypeptide chain.
• Determines all other levels of protein structure.
Primary
structure
Amino acids
PROTEINS
• Secondary structure forms because regions
of the polypeptide that are nonpolar are
forced together; hydrogen bonds can form
between different parts of the chain.
• The folded structure may resemble coils, helices,
or sheets.
Secondary
structure
β-pleated sheet
α-helix
O
PROTEINS
• Tertiary structure—the final 3-D shape of the
protein.
• The final twists and folds that lead to this shape
are the result of polarity differences in regions of
the polypeptide.
Tertiary
structure
PROTEINS
• Quaternary structure—the spatial arrangement of
proteins comprised of more than one polypeptide
chain.
Quaternary
structure
PROTEINS
• The shape of a protein
affects its function.
Folded
protein
• Changes to the
environment of the
protein may cause it to
unfold or denature.
• Increased
temperature or lower
pH affects hydrogen
bonding, which is
involved in the folding
process.
• A denatured protein is
inactive.
Denatured protein
PROTEINS
• Enzymes are
globular proteins
that have a special
3-D shape that fits
precisely with
another chemical.
• They cause the
chemical that they fit
with to undergo a
reaction.
• This process of
enhancing a
chemical reaction is
called catalysis.
Active-site
cleft
NUCLEIC ACIDS
Nucleic acids are very long polymers that
store information.
•
•
•
Comprised of monomers called nucleotides.
Each nucleotide has 3 parts:
1. a five-carbon sugar
2. a phosphate group
3. an organic nitrogen-containing base
NUCLEIC ACIDS
There are five different types of nucleotides.
•
Information is encoded in the nucleic acid by
different sequences of these nucleotides.
•
Nitrogenous bases
Structure of nucleotide Nitrogenous base
7N
Phosphate group
N
9
P
O–
O
H C
2
N
3
CH2
5
N C C N
H
N C N C H
H
C
1
3
2
OH
H C
OH in RNA
H C
R
Sugar
C
N
N
C O
Cytosine
(b)
N
C NH2
O
H
H in DNA
N C
Guanine
NH2
O
N C C N H
H
Adenine
4
(a)
4
O
NH2
N1
8
O
–O
5
NH2
6
H3C C
H C
C
N
O
N H
H C
C O
H C
H
Thymine (DNA only)
C
N
N H
C O
H
Uracil (RNA only)
NUCLEIC ACIDS
• There are two types of nucleic
acids:
• Deoxyribonucleic acid (DNA)
• Ribonucleic acid (RNA)
• RNA is similar to DNA except
that
• it uses uracil instead of thymine
• it is comprised of just one strand
• it has a ribose sugar
Sugar-phosphate
“backbone”
G
P
C
Hydrogen bonds
between nitrogenous
bases
P
T
A
P
Phosphodiester bond
P
C
G
P
P
A
T
P
OH
NUCLEIC ACIDS
• The structure of DNA is a double helix
because:
• There are only two base pairs possible
• Adenine (A) pairs with thymine (T)
• Cytosine (C) pairs with Guanine (G)
• Properly aligned hydrogen bonds hold each base
pair together.
• A sugar-phosphate backbone comprised of
phosphodiester bonds gives support.
A and C cannot properly
align to form hydrogen
bonds.
G and T cannot properly
align to form hydrogen
bonds.
A and T can align to form
two hydrogen bonds.
G and C can align to form
three hydrogen bonds.
NUCLEIC ACIDS
• The structure of DNA helps it to function.
• The hydrogen bonds of the base pairs can be
broken to unzip the DNA so that information can
be copied.
• Each strand of DNA is a mirror image so that the
DNA contains two copies of the information.
• Having two copies means that the information
can be accurately copied and passed to the
next generation.
CARBOHYDRATES
• Carbohydrates are monomers that make up
the structural framework of cells and play a
critical role in energy storage.
• A carbohydrate is any molecule that
contains the elements C, H, and O in a 1:2:1
ratio.
CARBOHYDRATES
• The sizes of carbohydrates varies:
• Simple carbohydrates—consist of one or two
monomers.
• Complex carbohydrates—are long polymers.
CARBOHYDRATES
• Simple carbohydrates
are small.
• Monosaccharides consist of
only one monomer subunit.
• An example is the sugar
glucose (C6H12O6).
• Disaccharides consist of
two monosaccharides.
• An example is the sugar
sucrose, which is formed
by joining together
glucose and fructose.
CARBOHYDRATES
• Complex carbohydrates are long polymer
chains.
• Because they contain many C-H bonds, these
carbohydrates are good for storing energy.
• These bond types are the ones most often
broken by organisms to obtain energy.
• The long chains are called polysaccharides.
CARBOHYDRATES
• Plants and animals store energy in
polysaccharide chains formed from glucose.
• Plants form starch.
• Animals form glycogen.
• Some polysaccharides are structural and
resistant to digestion by enzymes.
• Plants form cellulose cell walls.
• Some animals form chitin for exoskeletons.
LIPIDS
• Lipids—fats and other molecules that are
not soluble in water.
• Lipids are nonpolar molecules.
• There are many different types of lipids.
• fats
• oils
• steroids
• rubber
• waxes
• pigments
LIPIDS
• Fats are converted from glucose for longterm energy storage.
• Fats have two subunits
• 1. fatty acids
• 2. glycerol
• Fatty acids are chains of C and H atoms, known
as hydrocarbons.
• The chain ends in a carboxyl (—COOH) group.
SATURATED AND UNSATURATED
FATS
H
Because there
are 3 fatty acids
attached to a
glycerol,
another name
for a fat is
triglyceride
H
H
H
O H
H
H
H
H
H
H
H
C O
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
O H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
O H
H
H
H
H
H
H
H
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
C O
C O
H
Glycerol
backbone
Fatty acids
(a) Fat molecule (triacylglycerol)
H
H
H
LIPIDS
• Fatty acids have different chemical
properties due to the number of hydrogens
that are attached to the non-carboxyl
carbons
• If the maximum number of hydrogens are
attached, then the fat is said to be saturated.
• If there are fewer than the maximum attached,
then the fat is said to be unsaturated.
SATURATED AND UNSATURATED
FATS
H
H
H
H
C
C
C
C
H
H
(b) Hard fat (saturated): Fatty
acids with single bonds
between all carbon pairs
(c) Oil (unsaturated): Fatty acids
that contain double bonds
between one or more pairs
of carbon atoms
PHOSPHOLIPIDS
• Biological membranes involve lipids.
• Phospholipids make up the two layers of the
membrane.
• Cholesterol is embedded within the membrane.
Outside of cell
Carbohydrate chains
Cell
membrane
Membrane proteins
Inside of cell
Phospholipid
Cholesterol