# Thermodynamics and Metabolism

Mechanics

Oct 27, 2013 (4 years and 8 months ago)

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Thermodynamics and
Metabolism

Thermodynamics:

the
science of energy
transformations
(flow of
energy through living and non
-
living systems)

All living things require ENERGY

which is the capacity for doing work

Forms of energy:

thermal

light

chemical

electrical

KINETIC

ENERGY

Energy of
motion
:

Falling water

Pistons in a car engine

Skier going down a hill

Examples on a molecular scale
include the energy of
vibrations, random diffusion,
and heat.

POTENTIAL

ENERGY

stored

energy

Example
:
Molecules of
glucose have
potential energy,
stored in bonds

FIRST LAW OF THERMODYNAMICS

Energy can
neither be created nor destroyed
,
but can be transformed from one form to another.

eg: during photosynthesis, light energy from the Sun
is transformed into chemical energy
stored

in the
bonds of glucose

During cellular respiration, the energy in
the bonds of glucose is
released

and is
transformed into new molecules (ATP),
motion, and heat energy.

Photosynthesis and Respiration

Photosynthesis

Respiration

produces food

stores energy

uses water

u獥猠捡rbon d楯x楤e

releases oxygen

o捣cr猠楮 獵n汩ght

uses food

releases energy

produ捥猠wa瑥r

produces carbon
dioxide

u獥猠sxygen

occurs in the dark as
well as light

There is ALWAYS
some
loss of useful
energy
.

The Second LAW OF THERMODYNAMICS
:

Every energy transformation increases the
entropy of the universe.

The second law of thermodynamics

In all processes or reactions, some of the energy
involved irreversibly loses its ability to do work.

or

In any reaction the amount of molecular
disorder always increases

Entropy is a measure of the
randomness or disorder in a collection
of objects

Entropy increases…

when solids become liquids or gases

Complex molecules react to form simpler molecules
(catabolic reactions)

During diffusion

Living systems seem to
break the
second Law

of Thermodynamics

Anabolic processes
in cells build highly
ordered structures
(e.g.; proteins and
DNA
) from a
random
assortment of
molecules (
amino
acids and
nucleotides
) in the
cell fluids.

On a large scale, living organisms build and
maintain highly ordered structures such as cells,
tissues, organs and systems, as well as nests, webs
and homes.

All of these changes cause the universe to become
a little more ordered.

But these anabolic processes are coupled to catabolic
processes

Which release free energy
and thermal energy and
increase the entropy of the
universe.

Living organisms create
order in a local part of the
universe at the expense of
greater a greater amount
of disorder in the universe
as a whole.

Free energy

It is clear that
we should be
concerned only with
energy available to do
useful work, so
-
called
free energy or
Gibbs
energy
.

Josiah Willard

Gibbs

(1839
-

1903)

Exothermic Reactions

Produce energy (exergonic reactions)

Tend to increase entropy (therefore,
spontaneous)

-

delta G value

E.g.; cellular respiration

Exothermic Reaction

B) Endothermic Reactions

Require energy (endergonic reactions)

Tend to decrease entropy (because they create
big/organized molecules)

Are not spontaneous

+ delta G values

E.g.; photosynthesis

The
Transition state
describes the temporary conditions in which
the bonds within reactants are breaking and the bonds between
products are forming.

Activation Energy (E
A
)

:
amount of energy needed to
strain and break the reactants' bonds in a biochemical
reaction

For an
exergonic

reaction
,
D
G

is
negative
.

For an
endergonic reaction
,
D
G

is
positive
.

ATP

ATP is the
primary
source of
free
energy in
living cells.

ATP transports chemical energy within cells for
metabolism.

Metabolic processes that use ATP as an
energy source convert it back into ADP and
inorganic phosphate(P
i
)

precursors.

ATP is therefore continuously recycled in
organisms: the human body, contains
250

grams of ATP on average, and turns over
its own weight in ATP each day.

Phosphorylation

When ATP is used as an energy source, the
energy is NOT released as heat.

Instead, the hydrolysis of ATP is usually
coupled to a reaction which attaches the
phosphate group to another molecule directly
associated with the work that needs to be
done. (What example of this have you seen?)

Attaching the phosphate group
(phosphorylation) makes the other molecule
more reactive

Redox reactions

In living systems, free energy must be released
in small quantities.

The hydrolysis of ATP and the phosphorylation
of molecules is one way to accomplish this,

Another is coupled oxidation
-
reduction
reactions.

The transfer of electrons ( and H+) from one
substance to another is a way of transferring
free energy.

The electronegativity of each substance in the
“chain” must be greater than the molecule
that preceded it.

Redox reactions are used to create ATP.