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

1 st 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

2 nd 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 CO 2, H 2 O 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