Chapter 4 Energy and Cellular Metabolism

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University of Alberta
Physical Education and Sport
Michael Kennedy

Energy Is Used to Perform WorkAll living organisms obtain store and use energy to fuel their activities Energy can be defined as the capacity to do work but what is work In biological systems the word means one of three specific things chemical work transport work and mechanical work1 Chemical work enables cells and organisms to grow maintain a suitable internal environmentstore information needed for reproductionother activities It is the making and breaking of chemical bonds2 Transport work enables cells to move ions moleculeslarger particles through the cell membranethrough the membranes of organelles in the cell to create concentration gradients distribution of molecules in which the concentration is higher on one side of a membrane than on the other 3 Mechanical work is used for movement In a cellular level movement includes organelles moving around in a cell cells changing shapeciliaflagella beating At the macroscopic level in animals movement usually involves muscle contractionEnergy Comes in 2 Forms KineticPotentialWe speak of energy stored in chemical bonds All types of energy share an ability to appear in 2 forms1 Kinetic energy is the energy of motion ex Ball rolling down a hill heat warming a frying pan or electric charge flowing through power lines2 Potential energy is stored energy ex Ball on top of a hill has potential energy bcos it has the potential to start moving down the hillThe conversion from potential energy to kinetic energy is never 100 efficienta certain amount of energy is lost to the environment usually as heat Potential energy is stored in concentration gradientschemical bonds It is transformed into kinetic energy when needed to do chemical transport or mechanical workEnergy is Transferred Between Molecules During ReactionsUsing chemical reactions cells transform the potential energy of chemical bonds into kinetic energy for growth maintenance reproductionmovement A chemical reaction begins with 1 or more reactantsends with 1 or more products Table 42ABCDReaction rate is the disappearance rate of the reactants AB It is measured as the change in concentration of products with time The purpose of chemical reactions in cells is either to transfer energy from 1 molecule to another or to use energy stored in reactant molecules to do work The energy stored in the chemical bonds of a molecule available to perform work potential energy is the free energy of the molecule Complex molecules have more chemical bonds which means higher free energies ex Glycogen has more free energy than a single glucose molecule The high free energy of glycogen is the reason that these molecules are used to store energy in cells To understand how chemical reactions transfer energy between molecules we should answer 2 questions How do reactions get started Reactants need activation energy to be initiated for the reaction What happens to the free energy of the productsreactants during a reaction The difference between reactantsproducts is the net free energy change of the reactionEnergy Is Trapped or Released during ReactionsThe products of a reaction have either a lower free energy than the reactants or a higher free energy than the reactants A change in free energy level means that the reaction has either released or trapped energyIf the free energy of the products is lower than the free energy of the reactants Figure 43 b the reaction releases energy exergonic reaction or energyproducingEndergonic reactions or energyutilizing trap some activation energy in the products which then have more free energy than the reactants ex An endergonic reaction links many glucose molecules together to create glycogen
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