BIOL 1201 Lecture Notes - Lecture 2: Lipid Bilayer, Fluid Mosaic Model, Competitive Inhibition

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Biology Exam 2 Notes
Chemical Reactions
Chemical reactions: occur when two or more atoms, ions, or molecules
collide in such a way that they produce a new substance
o Must physically run into each other - in the right orientation and w/
sufficient force to produce the new substance
o They have to make a new substance chemically
o The way to make molecules go faster and make the reaction go faster
is to heat it up
Energetics of chemical reactions are governed by the 2 Laws of
Thermodynamics
o 1st Law: Energy can neither be created nor destroyed only converted
from one form to another
If reactants have less energy than products, must input energy
If reactants have more energy than products, energy must be
released
o 2nd Law: When converting energy from one form to another, the
amount of useful energy decreases (there is useable and non-usable
energy)
The conversion of energy is not 100% efficient and some
energy is lost
Most common form of non-useful energy (energy that has been
wasted) is the energy that is given off as heat
Body heat we give off is wasted energy of reactions in
our body
The more efficient the process is and the less waste energy
there is, the better it is for you you don’t have to take in as
much energy
Free Energy and Chemical Reactions
Spontaneous Reaction: one which can occur without outside help or energy
(exergonic: release free energy)
o Reactions that release free energy (exergonic)
Reactions can occur without any outside help
This doesn’t tell us anything about the speed of the reaction
o Have a negative G (going downhill energetically)
o Free energy in the system decreases
o )f everything was spontaneous you wouldn’t have to eat/breath very
much
Non-spontaneous Reaction: needs outside help (endergonic: require free
energy)
o Reactions that require the addition of free energy (endergonic)
Cannot occur without the addition of energy
o Have a positive G (going uphill energetically)
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o Free energy in systems increase
Free Energy (G)
Energy that is free and available to do useful work in the cell
The amount of energy that is released when reactions occur or the amount of
energy required in a process for a reaction to occur
[Figure 8.5]
o In each example, move from states of higher free energy to lower free
energy
Activation Energy (EA)
Energy required to get the reactants lined up properly
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o Energy required to get to the transition state
The larger the activation energy, the slower the reaction
Activation Energy does not change the G
Changes in Free Energy
Therefore, the question of interest to us: Is G positive or negative?
G = ∆H - TS
o G = change in free energy
o H = change in enthalpy
Enthalpy: heat energy of the system
Not the temperature, but rather the amount of heat
energy contained in the system
Example: Match at room temperature, but the chemicals in the
match have a lot of enthalpy
o T = temperature in Kelvins
All temperatures are positive numbers; no negative Kelvins
o S = change in entropy
Entropy: measure of disorder
Greater disorder, greater entropy (fewer molecules for
greater disorder)
Less disorder, lower entropy (more molecules for less
disorder)
Example: Lighting a Match
o Heat energy was released (which is why it gets hot)
Enthalpy of the match decreases when the match is lit (feel the
heat being released)
o Entropy increased instead of decreased (increased disorder)
Enthalpy decreased but entropy increased so the reaction was
spontaneous
o Reaction is spontaneous (energy did not need to be added)
Once you light the match it keeps burning you didn’t have to
keep adding energy
Free energy is negative; it decreased
Activation energy is extremely high (which is why you have to
strike the match to overcome the activation energy)
Example: Cooling pack crystals combine with water
o Both start off room temperature when combined it was cold
No extra energy was added spontaneous reaction
ΔG is negative (it is negative when it is a spontaneous
process)
o It is non-spontaneous when ΔG is positive
Did not release heat energy gets hot when releasing heat
energy
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