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The BIG Four
Molecules of Life: Biopolymers
Dr. Dale Hancock
[email protected]
Room 377
Biochemistry building
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Fat
Carbohydrate
Protein
Nucleic Acid
The BIG Four
General Biopolymer
properties:
• Fat
• Carbohydrate
•All linear biopolymers have a
defined beginning and end.
•Biopolymer synthesis is an
anabolic process (requires
energy input)
• Protein
• Nucleic Acid
General Biopolymer
properties cont.:
•All biopolymers are synthesized
in one direction only.
•Some of the monomer is lost in
polymerization, leaving a
“residue” incorporated in the
growing chain.
What is required for information
containing biopolymers?
Different
side chains
residue
Defined
start
Atom
with at
least 3
bonding
options
Common
Backbone
Defined
end
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Elements of Life
The unique properties of
Carbon
• They all come from the first 2 to 3
rows of the periodic table.
• C, H, O, N, P, S
• They all have small atomic radii
• They can form strong covalent
bonds.
• Life depends on carbon
• All major biopolymers have a
substantially carbon backbone
• It is not the most abundant
element on the earth’s crust;
O: 47%, Si: 28%, Al: 7.9%, Fe:
4.5%
Carbon in all its glory!!
The unique properties of
Carbon
• It can directly bond to itself and form
long chains.
• This property is known as
caternation.
• Side chains can “hang off” the
polymer backbone
The unique properties of
Carbon
The unique properties of
Carbon
• To form a polymer an element must have
at least 3 valence or bonding electrons;
after all a chain requires 2 bonds.
• Carbon forms 4 bonds.
• It must also form strong bonds with itself;
stronger than its bond with oxygen.
• There are 3 types of reactions that are
most likely to occur on this planet:
oxidation, hydrolysis and dissociation. The
oxygen and water vapour in the
atmosphere and the ambient temperature
of ~20o make oxidation and hydrolysis the
most likely reactions.
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The unique properties of
Carbon
So why is life carbon based
and not silicon based?
• Carbon is the only element with 4
bonding electrons which can form
strong bonds with itself.
BUT
• Doesn’t Silicon also form 4
bonds?
• Some geeks may argue life is
silicon based!!
• There is after all more silicon
in the earth
So why is life carbon based
and not silicon based?
The answer is glass!!
This is
life..but
not as we
know it!
Why is life not silicon based?
• Despite the fact that there is more
silicon in the earth’s crust than
carbon…
• Silicon readily forms strong bonds
with oxygen; stronger than with itself.
• Most of the silicon on earth exists as
silicates (O-Si-O) or glass (and
sand!)
Why is life not silicon based?
• Silicon has a larger atomic
radius…why would that be
significant?
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Why is life not silicon based?
• Silicon has a larger atomic
radius…why would that be
significant?
• The larger the atomic radius the
weaker the covalent bond.
The unique properties of
Carbon
• Carbon compounds are relatively inert or
kinetically stable to hydrolysis and
oxidation.
• In general organic reactions tend to be
under kinetic control rather than
thermodynamic control.
The unique properties of
Carbon
• This means that although the reaction is
thermodynamically favourable (the product
has less energy than the reactant) the rate
of reaction is so slow as to be almost nonexistent, due to a high activation energy.
This makes these reactions attractive for
enzyme control.
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