Transcript ENERGY - East Irondequoit Central School District

ENERGY
Intro to Cellular Metabolism
Metabolism:
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Metabolism – totality of an organism’s
chemical reactions
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Catabolic pathways – metabolic path that
releases energy by breaking down complex
molecules into simpler molecules
Anabolic pathways – metabolic path that
consumes energy to build complex molecules
from simpler molecules
Forms of Energy (capacity to cause
change)
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Radiant: sunlight, EM waves
Chemical: Glucose, ATP, Starch
Kinetic: Molecular movement (diffusion,
osmosis)
Heat
Mechanical: Muscle contraction
1st Law of Thermodynamics
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Energy may neither be created nor
destroyed; it may only be transferred or
transformed.
Thus in a closed system the total energy
remains constant.
Closed vs. Open Systems
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Organisms are open systems that exchange
materials with their environments
2nd Law of Thermodynamics
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At every energy transfer, some energy is
lost to the system (usually in form of heat)
This loss increases entropy (disorder)
Large Scale
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Energy flows into ecosystems as heat and
exits as heat radiated into space
Small Scale
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Animals take in organized forms of matter
and energy & replace them with less
ordered forms.
Ordered
Less ordered
Starch
Proteins
catabolized
CO2, H2O
Lipids
A word about “order”
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Systems rich in energy are highly ordered
Examples:
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Complex molecules
Human beings
Smaller parts (e.g. monomers of
macromolecules) have less energy and
are less ordered
Spontaneous processes
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Reactions that occur without outside help.
Ex: water flowing downhill
Release energy
For a rxn to be spontaneous, it must
increase entropy of universe
Spontaneous reactions
Non-spontaneous processes
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Require an input of energy
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Ex: Synthesize a protein
Decrease entropy in a system
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(a protein is more ordered than it’s amino acid
monomers)
Non-spontaneous reactions
Gibb’s Free Energy
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Free energy (G) is the portion of a system’s
energy that can perform work.
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Free Energy Change: ΔG = ΔH – TΔS
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H = total energy (enthalpy)
T = degrees in K
S = entropy
OR: ΔG = G(final state) – G(initial state)
Spontaneous Rxn:
ΔG = ΔH – TΔS
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For a rxn to be spontaneous, ΔG must be
negative
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Either decrease enthalpy (total energy)
Or increase entropy (give up order)
Endergonic vs. Exergonic
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Endergonic rxn – absorbs free energy
from surroundings (ΔG is positive)
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Creates more order (anabolic)
Exergonic rxn – releases free energy into
surroundings (ΔG is negative)
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Creates more disorder (catabolic)
Metabolic Equilibrium
( a very, very bad thing)
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Reactions in a closed system reach
equilibrium
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ΔG will be 0; no work can be done.
A cell that reaches metabolic equilibrium is
dead!
Key to preventing equilibrium =
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The product of one reaction becomes the
reactant in the next.
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i.e. Products do not accumulate
Energy coupling: the use of an exergonic
reaction (release energy) to power an
endergonic (requires energy) reaction.
Example:
ATP! (adenosine triphosphate)
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Energy source that powers cell’s activities