BISC 1111 Chapter Notes - Chapter 8.1-8.4: Exergonic Reaction, Atp Hydrolysis, Thermal Energy

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Samuel Mohebban Chapter 8.1-8.4 Exam 2
1
Metabolism- totality of an organism’s chemical reactions.
A metabolic pathway begins with a specific molecule, which is then altered in a series of defined
steps, resulting in a certain product.
Catabolic pathways- release energy by breaking down complex molecules to simpler compounds
o Ex: cellular respiration
Anabolic pathways- consume energy to build complicated molecules from simpler ones.
o Ex: synthesis of an amino acid from simpler molecules and the synthesis of a protein from
amino acids.
Energy is the capacity to cause change.
o Kinetic Energy- energy associated with relative motion of objects.
o Thermal Energy- kinetic energy associated with the random movement of atoms or
molecules.
Thermal energy in transfer from one object to another is called heat.
o Potential energy- energy that matter possesses because of its location or structure. (not
kinetic)
o Chemical energy = potential energy available for release in a chemical reaction.
Thermodynamics- study of the energy transformations that occur in a collection of matter.
o System = matter under study
o Surroundings = everything outside the system
First law of thermodynamics- the energy of the universe is constant
o Energy can be transferred and transformed, but it cannot be created or destroyed.
Entropy- is a measure of disorder, or randomness.
o The more randomly arranged a collection of matter, the greater its entropy.
Second law of thermodynamics- every energy transfer or transformation increases the entropy of the
universe
Spontaneous Process- if a given process leads to an increase in entropy, then that process can
proceed without requiring an input of energy
The entropy of a particular system, such as an organism, may decrease as long as the total entropy of
the universe (system + surroundings) increases.
Free energy- is the portion of a system’s energy that can perform work when temperature and
pressure are uniform throughout the system, as in a living cell.
o ∆G = ∆H – T∆S
(∆H = change in enthalpy, ∆S = change in system’s entropy, T = absolute temp)
If ∆G is negative = spontaneous
Every spontaneous process decreases the system’s free energy,
o Processes that have a positive or zero ∆G are never spontaneous.
G = G (final) G (initial)
o G is only negative when the process involves a loss of free energy during the change form
initial state to final state.
o Because the final state has less free energy, the system is less likely to change and therefore is
more stable than before.
As a reaction proceeds toward equilibrium, the free energy of the mixture of reactants and products
decreases.
Free energy increases when a reaction is pushed away from equilibrium.
G is at its lowest possible value for a system at equilibrium.
Any change from equilibrium will have a +∆G and will not be spontaneous.
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Samuel Mohebban Chapter 8.1-8.4 Exam 2
2
A process is spontaneous and can perform work only when it is moving toward equilibrium
An Exergonic reaction proceeds with a net release of free energy. (-∆G) [Spontaneous]
An Endergonic reaction is one that absorbs free energy from its surroundings. (+∆G)
[Nonspontaneous]
If a chemical process is exergonic, then the reverse process must be endergonic.
A living cell is not in equilibrium.
o The constant flow of materials in and out of the cell keeps the metabolic pathways from ever
reaching equilibrium, and the cell continues to do work throughout its life.
A cell does 3 main kinds of work:
o 1) Chemical work = the pushing of endergonic reactions that would not occur
spontaneously, such as the synthesis of polymers from monomers.
o 2) Transport work = the pumping of substances across membranes against the direction of
spontaneous movement.
o 3) Mechanical work = such as the beating of cilia, the contraction of muscle cells, and the
movement of chromosomes during cellular reproduction.
Energy coupling- the use of an exergonic process to drive an endergonic one,
o ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as
the immediate source of energy that powers cellular work.
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