Metabolism Lecture 5, part 1 Fall 2008

Metabolism All the biochemical process within an organism that maintain life and contribute to growth Emergent properties –The whole is greater than the sum of its parts –New properties emerge with each step upward in the hierarchy of life Cellular metabolism arises from interactions between molecules within the orderly environment of the cell 1

Metabolism Metabolic pathway –Series of chemical reactions Catabolic pathway –Breaks down a complex molecule into simpler compounds –Creates energy Anabolic pathway –Builds a complex molecule from simpler compounds –Consumes energy Bioenergetics –Study of how energy flows through living organisms 2

Energy The capacity to cause change The ability to rearrange a collection of matter Two main types Kinetic energy Potential energy 3

Energy Kinetic energy Energy of motion –Does work by imparting motion to other objects Thermal energy (heat) –Type of kinetic energy –Amount of energy associated with the random movement of atoms and molecules –Temperature Measure of how much thermal energy a molecule possesses The faster the molecule, the more collisions, the higher the temperature 4

Energy Potential energy Stored energy Based on location or structure Chemical energy –Form of potential energy available for release in a chemical reaction 5

Chemical Energy Chemical energy Energy stored in chemical bonds –Released when bonds between molecules broken Produces heat, kinetic energy and waste products Amount of kinetic energy produced is how efficient the process is –Car: 25% kinetic energy – rest is lost as heat –Cellular respiration: 40% cellular work, rest is used for body heat 6

Review Chemical Bonds, pg Covalent Ionic Hydrogen 7

Energy Transformation Energy can change from potential to kinetic and back 8

Energy Transformation Energy can change from potential to kinetic and back Fig

Energy & Thermodynamics Thermodynamics Study of energy transformations that occur in a collection of matter First Law of Thermodynamics (Principle of Conservation of Energy) –Energy is neither created nor destroyed, only converted from one form to another –Amount of matter & energy in the universe remains the same –Energy is always conserved Can be converted from one form to another. e.g. photosynthesis converts energy from the sun into plant biomass. Energy quantity stays the same 10 Fig.8.3

Energy & Thermodynamics Second Law of Thermodynamics –When energy is changed from one form to another, some of the useful energy is always degraded to lower-quality, more dispersed, less useful energy. Usually heat –e.g. cellular respiration glucose + oxygen = carbon dioxide + water + energy (+ heat) Energy quality is changed 11 Fig.8.3

Energy & Entropy Entropy –amount of disorder in a group of molecules –Heat - high disorder, high entropy, less useful form of energy Second Law of Thermodynamics (revisited) Every energy transformation increases the entropy of the universe Cells are not disordered – use energy to fight entropy Organisms are “islands of low entropy in an increasingly random universe” 12

How do chemical reactions happen? Reactants –starting materials Products –resulting materials Balanced equations Matter is neither created nor destroyed, only rearranged –Breaking and forming of chemical bonds 13

How do chemical reactions happen? 3H 2 + N 2 → 2NH 3 ← Reaction is reversible Chemical equilibrium –A dynamic but stable state of a reversible chemical reaction in which the forward reaction and reverse reaction proceed at the same rate, so that the concentrations of reactants and products remain constant –Changing chemical equilibrium Changing concentration of reactants or products Changes in temperature (e.g., gas to liquid) 14

How do chemical reactions happen? What makes a chemical reaction spontaneous? –Proceed on their own without any continuous external influences (energy) Reactions tend to be spontaneous if: 1. the products have lower potential energy than the reactants 2. when the product molecules are less ordered than the reactant molecules 15

What makes a chemical reaction spontaneous? 1. Reactions tend to be spontaneous if the products have lower potential energy than the reactants Products have lower potential energy if their electrons are held more tightly than electrons of reactants More electronegative –Electronegativity –The tendency of an atom to attract electrons towards itself 16

What makes a chemical reaction spontaneous? Enthalpy (ΔH) –Measure of difference in energy between reactants and products –When reaction is exothermic ΔH is negative Exothermic –Chemical reaction that releases heat Endothermic –Chemical reaction that absorbs heat 17

What makes a chemical reaction spontaneous? 2. Reactions tend to be spontaneous when the product molecules are less ordered than the reactant molecules Entropy (S) –amount of disorder in a group of molecules – Δ S is positive when products are less ordered than reactants –Spontaneous reactions increase entropy 18

Free Energy Physical and chemical process proceed in direction that results in lower potential energy (negative ΔH) and increased disorder (positive ΔS) Gibbs free-energy change (ΔG) Free energy –The portion of a system’s energy that can perform work when temperature and pressure are uniform throughout the system (e.g., living cell) ΔG = ΔH - T ΔS T= temperature in Kelvin –Temperature becomes more important in determining free-energy change as the temp of molecules increases Fig

Free Energy ΔG = ΔH - T ΔS If ΔG is less than 0, reaction is spontaneous = exergonic –Net release of free energy If ΔG is greater than 0, reaction is not spontaneous = endergonic –Absorbs free energy from its surroundings –Stores free energy in molecules Fig

Free Energy & Equilibrium When ΔG is zero, reactions are at equilibrium –Free energy decreased –Systems cannot spontaneously move away from equilibrium Living cells not at equilibrium –Products become reactants in other metabolic pathways 21

ATP & Cellular Work Three main types of work Mechanical –E.g. moving cilia, contracting muscles Transport –Transport of molecules across cell membrane Chemical –Promoting chemical reactions that do not happen spontaneously (endergonic) Most cellular work done by ATP 22

ATP & Cellular Work ATP (adenosine triphosphate) Adenine (nitrogenous base) Ribose (sugar) 3 phosphate groups –Phosphate groups negatively charged –Repelling of charges = high potential energy Unstable molecule –Hydrolysis breaks bond of terminal phosphate group –Products: Adenosine diphosphate (ADP) and inorganic phosphate –Exergonic: releases energy 7.3 kcal per mole ATP 23 Fig. 5.5

ATP & Cellular Work Phosphate Transfer Phosphorylation –Transfer of the phosphate group from ATP to some other molecule This phosphorylated molecule undergoes a change that performs work –More reactive/less stable –Conformation change –Phosphorylated = molecule that receives the phosphate group Fig

ATP & Cellular Work Energy coupling Transfer of energy from processes that yield energy (exergonic) to processes that consume energy (endergonic) Fig

ATP & Cellular Work ATP recycling ATP used continuously by organism ADP+ inorganic P brought together again via cellular respiration –Very rapid - 10 million ATP molecules spent & regenerated per second per active muscle cell 26 Fig. 8.12