What is Biochemistry?
• A science that integrates life with chemistry
• A science that attempts to determine how
lifeless molecules combine to give the
attributes of life
• A science that operates by the principle that
life’s molecules are selected for the functions
• A science that delves into the world of the
unseen for answers to life’s mysteries.
What are the Challenges of Biochemistry?
To understand the chemical complexity of a cell
To determine how cells are able to extract and transform
energy from their surroundings
To learn how cells are capable of self-replication
To determine how cells sense and respond to changes
in their environment
To understand the structural logic behind the selection
of specific molecules for specific tasks
How does Biochemistry Differ from
• Organic chemistry is the chemistry of
carbon compounds. Biochemistry is the
study of carbon compounds that crawl
A Biochemist is a person who can’t tell the difference between a
plant or an animal
What are the Objectives of
• To introduce students to the properties of
molecules found in living cells.
• To compare and contrast the properties of
molecules in the different categories.
• To demonstrate the structure-function
principle of biochemistry.
• To threaten, cajole, or otherwise persuade
students that a knowledge of biochemistry
is essential to understanding the properties
Molecules of Life
Take Home: Weak and strong forces hold biomolecules
Important Functional Groups in Biomolecules
Important Functional Groups (Continued)
CH2 O-P-O CH2-CH2-N(CH3)3
Light to electrical
Chemical to mechanical
Sound to electrical
Q: How do we know when a given reaction or process will
occur spontaneously or in a favored direction?
A: Berthelot (1860) All spontaneous reactions occur with
the liberation of heat. Therefore, spontaneous reactions
A: Gibbs (1870). Heat is not the only index of spontaneity.
Many spontaneous processes occur without liberating heat.
The order or entropy must also be considered.
Q: Is it possible for a reaction to actually absorb heat or
remain isothermal and still be favored in one direction?
Q: Can you give an example?
A: When ice melts or salt dissolves in water or when a gas
confined to one chamber diffuses to occupy two chambers,
these are spontaneous reactions that absorb heat.
Q: So, knowing the favored direction must account for
both energy release and order.
A: Yes, energy as heat is called enthalpy. Enthalpy change
or H measures energy released at constant pressure. In a
favored reaction H is less than 0, i.e., H is negative.
Entropy is a probability function. The probability that the
system will exist in any form other than perfect order. In a
favored reaction entropy change or S is positive.
The combination gives rise to a state function called the
free energy. A reaction will always be favored in the direction
that free energy change is negative or less than 0.
Q: Can you give me a equation that helps me see this
Maximal (– G)
G = H - TS
occurs when H
is negative and
S is positive
Energy Change at constant pressure
Energy locked in chemical bonds
Glucose + 6O2
6CO2 + 6H2O
H = heat evolved
Take Home: Because energy differential is independent
of path taken, energy from combustion in a bomb
calorimeter is the same as in the body
Oxidation of Palmitic Acid (C16H32O2)
p = heat evolved at constant
At constant pressure and volume, no work has been
done against or by the surroundings.
At constant P, if
can do work on
the system… more
heat can be evolved
q=E + w
w = PV
w = nRT
CH3(CH2)14COOH + 23O2
16CO2 + 16H2O
Relates to molecular order
Energy unavailable during a chemical transition
“A spontaneous reaction is one that favors movement
from order to disorder…occurs with a positive change
“To go from disorder back to order requires input
Take Home: Living system take chemicals from their
disordered environment and assemble them into ordered
arrays of structural molecules. Hence, living systems live
on NEGATIVE entropy.