energy intro to cellular metabolism. metabolism: metabolism – totality of an organism’s chemical...
TRANSCRIPT
ENERGY
Intro to Cellular Metabolism
Metabolism: Metabolism – totality of an organism’s
chemical reactions 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)
Radiant: sunlight, EM waves Chemical: Glucose, ATP, Starch Kinetic: Molecular movement (diffusion,
osmosis) Heat Mechanical: Muscle contraction
1st Law of Thermodynamics
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
Organisms are open systems that exchange materials with their environments
2nd Law of Thermodynamics At every energy transfer, some energy is
lost to the system (usually in form of heat) This loss increases entropy (disorder)
Large Scale
Energy flows into ecosystems as heat and exits as heat radiated into space
Small Scale
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”
Systems rich in energy are highly ordered Examples:
Complex molecules Human beings
Smaller parts (e.g. monomers of macromolecules) have less energy and are less ordered
Spontaneous processes
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
Require an input of energy Ex: Synthesize a protein
Decrease entropy in a system (a protein is more ordered than it’s amino acid
monomers)
Non-spontaneous reactions
Gibb’s Free Energy Free energy (G) is the portion of a system’s
energy that can perform work.
Free Energy Change: ΔG = ΔH – TΔS H = total energy (enthalpy) T = degrees in K S = entropy
OR: ΔG = G(final state) – G(initial state)
Spontaneous Rxn:
ΔG = ΔH – TΔS
For a rxn to be spontaneous, ΔG must be negative
Either decrease enthalpy (total energy) Or increase entropy (give up order)
Endergonic vs. Exergonic
Endergonic rxn – absorbs free energy from surroundings (ΔG is positive) Creates more order (anabolic)
Exergonic rxn – releases free energy into surroundings (ΔG is negative) Creates more disorder (catabolic)
Metabolic Equilibrium( a very, very bad thing)
Reactions in a closed system reach equilibrium ΔG will be 0; no work can be done.
A cell that reaches metabolic equilibrium is dead!
Key to preventing equilibrium =
The product of one reaction becomes the reactant in the next. 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)
Energy source that powers cell’s activities