Biology 1002B Lecture Notes - Lecture 4: Gibbs Free Energy, Exergonic Reaction, Exergonic Process

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15 Feb 2016
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Professor
Lecture 4: Energy and Enzymes Anuj Gupta 01/13/16
cells as open systems and how they maintain low entropy
Chlamy (as well as cells) are open systems (energy and matter are freely exchangeable
with the environment).
Energy can be used as work to move or build macromolecules. Takes work to do so. But
not all E is used because some is lost as entropy or energy spreading.
Entropy causes or will cause everything to breakdown.
Cells maintain low entropy by always taking in energy and matter.
However this comes at a cost. The S of the environment around the cell drastically
increase due to the cell constantly giving off waste and heat.
You need to eat to maintain low
entropy because the entropy is always
causing stuff to breakdown (this
process CANNOT be stopped). By
constantly getting energy you can
counteract this by keeping the entropy
low.
oThat is why transcription is
always occurring or
housekeeping genes are always
on. Even if a cell has lots of
actin, its not going to stop
making it since the actin will
breakdown due to S.
Components of Gibbs Free Energy equation and how they affect whether or not a reaction
will be spontantous
∆ G=∆ HT ∆ S
(G is gibbs free energy, enthalpy, S is entropy, T is temperature)
oFor example the amount of energy glucose contains is ∆H, the amount lost to heat
is T∆S, and the amount that you can actual utilize is ∆G.
If ∆H is
o+ Endothermic
o- Exothermic
If ∆G is
o+ Endergonic
o - Exergonic
If T∆S is
o+ More spread out
o- Less spread out
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For example, if a reaction proceeds as A B, then the sign of ∆G indicates whether a
reaction will be SPONTANEOUS (this reaction will not require any energy. This reaction
will not require any aid to occur) or not. If a reaction is spontaneous than ∆G is -.
Exergonic reaction energy profile
Occurs if ∆Gi is -. This means is the reaction is spontaneous. This means that Gproducts
< Greactants . The free energy of the products (B) is less than the free energy of the reactans.
Both enthalpy (H) and entropy (S) INDEPENDENTLY contribute to the change in
Free Energy (G).
For example the fermentation of glucose to
ethanol.
oIts exergonic since ∆G is - , and its
exothermic since ∆H is – and energy
is given off.
oIncrease in disorder in products
compare to reactants.
We know that entropy is
going to increase because the
# of molecules increase, and
a phase change occurs (more
energy spreading)
Another example, the melting of ice.
oThe reaction is exergonic (ice melts
spontaneously) but its endothermic.
oThe glass is heating up since it’s absorbing
energy from the environment.
oHowever there is a massive increase in
entropy. Even though ∆H is +, T∆S > ∆H
resulting in a –∆G.
Transition state and energy of activation
Transition state always a slightly higher energy state. That’s the point where molecules
have the highest G (even more than normal reactants would) before it G goes down and
the reactants are converted to products.
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