Thermodynamics and Metabolism

bronzekerplunkMechanics

Oct 27, 2013 (4 years and 16 days ago)

75 views

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.