Thermodynamics & Cell energetics

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Thermodynamics &

Cell
energetics

Section 1.3 Pgs. 58
-
68

THERMODYNAMICS

Energy


Defined as the ability to
do work
(to transfer energy by
applying a force on an object.)



Classifying energy:

Energy


Kinetic Energy

the energy an object
possesses due to
movement


Potential Energy

stored energy

Chemical energy



The energy stored in
chemical bonds.


A type of potential energy.


Recall: Energy is stored in a bond when it forms, and is
released when that bond is broken.

Thermodynamics


The branch of physics that studies the
conversion of different forms of energy

Laws of Thermodynamics

First law:

The Law of Conservation of Energy


“Energy cannot be created or destroyed, it can
only be converted to other forms.”


Implication: If an object in the universe gains energy,
another one has lost.

Second law
:


Every transfer or transformation of energy
results in an overall increase in the disorder of
the universe.


This disorder is called “entropy”.

Two important thermodynamic quantities:


1.
Enthalpy (
Δ
H)

2.
Entropy (
Δ
S)

Enthalpy (
Δ
H)

Enthalpy

-

The heat content of the
molecule.


Bond energy is the energy stored in a
chemical bond.

Measured as the amount of energy required to
break

one mole of that chemical bond
(kJ/mol)


The higher the bond energy, the more
stable it is (harder to break).



Change in enthalpy
(
Δ
H)
is a measure of
the change in bond energy between
reactants and products.

Δ
H

Heat energy is...

Bond energy

> 0

absorbed

products > reactants

< 0

released

products

< reactants

Entropy (
Δ
S)



A measure of the
randomness

or
disorder

in energy, in a system.



Increases in entropy:


solid


liquid


gas


fewer moles of reactants


greater moles of
products


complex molecules


simple molecules


diffusion

The universe favours...

1.
Decrease in enthalpy

2.
Increase in entropy

Free energy (
Δ
G)


There may be a lot of energy within a
system, but not all of it is available to do
work.

Refer to pg. 62 in your text for a detailed illustration of this concept



The energy that is available for work is
referred to as
Gibbs free energy.


...is one that does not require an initial
input of energy in order to occur.


A process is spontaneous if
ΔG
is positive
(free E is released).



exergonic



If
ΔG

< 0, free E is absorbed


process is
not spontaneous. “
endergonic


Three factors influence
ΔG
:

a.
ΔH

b.
ΔS

c.
Temperature


See Table 2 on pg. 61 for a description of how these factors are
related.

CELL ENERGETICS

Metabolism


Catabolism:


Macromolecules


Subunits.


Energy is released.



Anabolism:


Subunits


Macromolecules.


Energy is required.



Metabolism = Anabolic + Catabolic
processes

Metabolic processes


All are catalyzed


All are reversible: e.g.

glucose ↔ starch



If a reversible reaction reaches
equilibrium,
Δ
G = 0


Dead cell


Avoided by removing products and
byproducts of metabolic reactions.


Endergonic reactions are closely coupled
with exergonic ones

Redox

reactions

...involve the transfer of electrons



Oxidation = Loss of electrons = Loss of E


Reduction = Gain of electrons = Gain of E




Substances that are reduced are called
oxidizing agents
.



Substances that are oxidized are called
reducing agents
.

Redox

series


Electrons are passed from one substance to
another.














Electron moves to successively stronger
electron acceptors





Free energy is released at every step.

Redox

by partial transfer

Oxidation

Reduction



loss of electrons


loss of energy


loss

of hydrogen


gain of oxygen (or another,
more electronegative atom:
F,
Cl
, Br)


gain of electrons


gain of energy


gain

of hydrogen


loss of oxygen, etc

Electron carriers: NAD
+,
FAD


Electron carriers serve as
temporary

holding stores for E.


They get
reduced
.


a)
NAD
+

NAD
+

+ 2e
-

+ H
+



NADH


b)
FAD


FAD + 2e
-

+ 2H
+



FADH
2


Adenosine
triphosphate

(ATP)


Primary source of free energy in living
cells.



Composed of:


adenine


ribose


3 phosphate (PO
4
) groups



PO
4

groups are negatively charged


unstable



Hydrolyzing the bond between the 2
nd

and 3
rd

PO
4
releases free energy


ATP + H
2
O


ADP + P
i

+ 31 kJ/mol



Catalyzed by ATPase


Exergonic


Product (ADP) is more stable

Formation of ATP


Phosphorylation


Attachment of a PO
4
group to an organic molecule



ADP is phosphorylated


ATP


ADP + P
i



ATP


a.
Substrate
-
level phosphorylation

b.
Oxidative phosphorylation

a. Substrate
-
level
phosphorylation


Direct transfer of a P
i

group from another
compound



Enzyme
-
catalyzed


Stores 31 kJ/mol


Endothermic &

endergonic


b. Oxidative
phosphorylation


Indirect



Powered by the energy released by a
series of redox reactions


You’ll learn more about this later...

Much much much more.

ATP and ADP are constantly being recycled

Homework

Pg. 68

#2
-
7, 9a, 10