Introduction to
Metabolism
How the Universe Really Works
What is Energy?

Capacity to do work

Forms of energy
Electrical
 Mechanical
 Chemical
 Light
 Heat

What is Energy?

Capacity to do work

Forms of energy
Potential energy
 Kinetic energy

Kinetic and potential energy: dam


Stored Water =
Potential Energy
Moving Water =
Kinetic Energy
Kinetic and potential energy: cheetah at rest and running

Cheetah resting =
Potential Energy
Cheetah running =
Kinetic Energy

Energy can be converted from one form to
another.



As the boy climbs the ladder to the top of the slide
he
is converting his kinetic energy to potential energy.
As he slides down, the
potential energy is
converted back to
kinetic energy.
It was the potential energy
in the food he had eaten
earlier that provided the
energy that permitted him
to climb up initially.
Fig. 6.2
One-Way Flow of Energy



The sun is life’s primary energy source
Producers trap energy from the sun and
convert it into chemical bond energy
All organisms use the energy stored in
the bonds of organic compounds to do
work
What Can Cells Do
with Energy?

Energy inputs become coupled to
energy-requiring processes

Cells use energy for:

Chemical work

Mechanical work

Electrochemical work
Energy Relationships
large energy-rich molecules
(fats, complex carbohydrates,
proteins, nucleic acids)
ADP + Pi
BIOSYNTHETIC PATHWAYS
(ANABOLIC)
DEGRADATIVE PATHWAYS
(CATABOLIC)
ATP
energy-poor products
such as carbon dioxide, water
ENERGY INPUT
simple organic compounds
simple sugars, amino acids,
fatty acids, nucleotides
Thermodynamics

Thermodynamics is the study of energy
transformations.

system indicates the matter under study and the
surroundings are everything



closed system is isolated from its surroundings.
In an open system energy (and often matter) can be
transferred between the system and surroundings.
Organisms are open systems.

They absorb energy - light or chemical energy in organic
molecules - and release heat and metabolic waste
products
First Law of Thermodynamics


The total amount of energy in the
universe remains constant
Energy can undergo conversions from
one form to another, but it cannot be
created or destroyed
Second Law of
Thermodynamics

No energy conversion is ever 100
percent efficient

The total amount of energy is flowing
from high-energy forms to forms
lower in energy
Two laws of thermodynamics


Conversion of energy from chemical potential
to kinetic mechanical energy.
Some energy is lost to heat.
Entropy


Measure of degree of disorder in a
system
The world of life can resist the flow
toward maximum entropy only because it
is resupplied with energy from the sun
Free Energy

Free energy can be thought of as a
measure of the stability of a system.
Systems that are high in free energy compressed springs, separated charges - are
unstable and tend to move toward a more
stable state - one with less free energy.
 Systems that tend to change spontaneously
are those that have high energy, low entropy,
or both.


In any spontaneous process, the free
energy of a system decreases.
Energy changes in exergonic and endergonic reactions
The Math

We can represent this change in free energy
from the start of a process until its finish by:



delta G = G final state - G starting state
Or delta G = delta H - T delta S
For a system to be spontaneous, the system
must either give up energy (decrease in H),
give up order (decrease in S), or both.



Delta G must be negative.
The greater the decrease in free energy, the
greater the maximum amount of work that a
spontaneous process can perform.
Nature runs “downhill”.
Still Calculating

The magnitude of delta G for an exergonic
reaction is the maximum amount of work the
reaction can perform.

For the overall reaction of cellular respiration:




C6H12O6 + 6O2 -> 6CO2 + 6H2O
delta G = -686 kcal/mol
Through this reaction 686 kcal have been made
available to do work in the cell.
The products have 686 kcal less energy than the
reactants
Endergonic Reactions

Energy input
required

Product has more
product with
more energy
(plus by-products
602 and 6H2O)
energy than starting
ENERGY
IN
substances
6
12
Exergonic Reactions


Energy is
released
Products have
less energy than
starting
substance
energy-rich
starting
substance
ENERGY
OUT
+
602
6
6
products with less energy
Participants in
Metabolic Pathways
Substrates

Energy Carriers
Intermediates

Enzymes
End

Cofactors
products