# Energy Use In cells

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Energy Use In cells. Matter anything that has mass and takes ups space Energy - capacity to do work or bring about change Matter is a form of energy [ E=mc 2 ] > 4 billion kg of matter per second are converted into energy in the sun - PowerPoint PPT Presentation

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Energy Use In cells

Energy Use In cellsEnergy & MetabolismMatter anything that has mass and takes ups spaceEnergy - capacity to do work or bring about change Matter is a form of energy [ E=mc2 ] > 4 billion kg of matter per second are converted into energy in the sunEnergy is expressed as units of work kilojoules (kJ) or as heat energy kilocalories (kcal)

Energy and MetabolismEnergy flows as heat energy from an object with a higher temperature to an object with lower temperatureCells are too small to have regions with different temperatures, so biologists talk about work energy (kJ)Organisms carry out conversions between potential energy (stored/position) and kinetic energy (motion)Chemical energy is PE stored in chemical bondsThermodynamicsThermodynamics study of energy and its transformationFirst Law: energy cannot be created or destroyed. It can only be transferred or converted from one form to another.Mass/energy present 14 billion years ago =todays mass/energyOrganisms cant create own energy have to capture it from the environment and transform it into a form used for biological workThermodynamicsSecond law When energy is converted from one form to another, some usable energy (energy available to do work) is converted to heat. Heat is the KE of randomly moving particles. This heat the random motion of particles- cannot do work. Amount of usable energy in the universe decreases over timeEnergy is constant, but usable energy is decreasingThermodynamicsLess-usable energy is more diffuse and disorganized.Entropy (S) is a measure of this disorder.Organized usable energy has low entropy.Disorganized energy (i.e. heat) has high entropy.As a result of 2nd Law, the cells net energy conversion is about 40% efficient.Organisms maintain a high degree of organization, why dont they wind down?Organisms are open systems. They exchange energy and materials with the environment. Organization is maintained through a constant input of energy.Plants do photosynthesisAnimals eatMetabolismMetabolism is the sum of all chemical activities in an organism.Anabolism complex molecules made from simpler substancesCatabolism larger molecules broken down into smaller onesThese are complementary processes.Catabolism results in overall release of energyAnabolism requires overall input of energyMetabolismIn order to talk about how much usable energy is available to a cell, we talk about Enthalpy (H) total PE of a system, Entropy (S) disorder and Free Energy (G) energy available to do work in biochemical reactionsG = H T(S) As entropy of a system increases, the amount of free energy decreases.When we measure the temperature difference of a process, we are measuring the enthalpy (PE) change of the system.

If T is +, then heat has been released from the system, H is (exothermic)

If T is -, then heat has been absorbed by the system, H is + (endothermic)MetabolismExergonic reactions release energy. This means that the products have less free energy than was present in the reactants. The free energy of the system (energy available to do work) decreases and G is considered to be negative. (G = - )

Endergonic reactions absorb energy, the products have more free energy than the reactants, the free energy of the system increases and G is positive. (G = +)Metabolism- G (exergonic) means that the reaction occurs without input of additional energy (the reaction is considered to be spontaneous).

+G (endergonic) means that the reaction requires input of energy to proceed (the reaction is considered to be non-spontaneous).

In organisms, endergonic reactions (reactions that are driven by energy input) are coupled with exergonic reactions (reactions that are spontaneous and release usable energy). Free energyDiffusion is exergonic. Diffusion goes down a concentration gradient. There is PE in a concentration gradient. Cell uses energy to produce this concentration. A region with a high concentration is more ordered (has lower entropy)than a region with low concentration. As particles move around randomly, they become more disordered (they now have higher entropy). As they gain higher entropy, they have less free energy. This is exergonic and the energy released can be used for cellular work.ChemiosmosisG depends on concentration of reactants and products.Any process that increases randomness (increases entropy) can do work because free energy is increased: G = H TSAs S (randomness) increases, G becomes more negative. -G = exergonic

Exergonic means it is free energy- releasing. This means that energy is made available to the cell to do cellular work. Formation of ATP through chemiosmosis is an example of the use of a Hydrogen ion concentration gradient this way.