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This overview delves into the essential concepts of cellular metabolism, emphasizing the two key pathways: catabolic, which releases energy by breaking down complex molecules, and anabolic, which consumes energy to build complex ones. We explore various forms of energy, the laws of thermodynamics, and the significance of spontaneous and non-spontaneous processes. Additionally, the role of Gibbs Free Energy in determining reaction spontaneity and the critical importance of energy coupling to prevent metabolic equilibrium are highlighted, ultimately suggesting how organisms maintain vitality through energy transformations.
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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. OrderedLess 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
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)
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.
ATP! (adenosine triphosphate) • Energy source that powers cell’s activities
