Chapter 3

# Chapter 3 - Reginald H Garrett Charles M Grisham Chapter 3...

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Reginald H. Garrett Charles M. Grisham Chapter 3 Thermodynamics of Biological Systems

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Essential Question What are the laws and principles of thermodynamics that allow us to describe the flows and interchanges of heat, energy, and matter in biochemical systems?
3.1 What Are the Basic Concepts of Thermodynamics? Figure 3.1 The characteristics of isolated, closed, and open systems. Isolated systems exchange neither matter nor energy with their surroundings. Closed systems may exchange energy, but not matter, with their surroundings. Open systems may exchange either matter or energy with the surroundings.

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The First Law – The Total Energy of an Isolated System is Conserved E (or U) is the internal energy - a function that keeps track of heat transfer and work expenditure in the system E is heat exchanged at constant volume E is independent of path E 2 - E 1 = E = q + w q is heat absorbed BY the system w is work done ON the system Thus both q and w are positive when energy flows into a system
Enthalpy Enthalpy – a better function for constant pressure H = E + PV If P is constant, H = q H is the heat absorbed at constant P Volume is approx. constant for biochemical reactions (in solution) So H is approx. same as E for biochemical reactions

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3.1 What Are the Basic Concepts of Thermodynamics? Positive values of ΔH would be expected for the breaking of hydrogen bonds as well as for the exposure of hydrophobic groups from the interior of a native, folded protein during the unfolding process. Such events raise the energy of the protein solution.
The Second Law – Systems Tend Toward Disorder and Randomness Systems tend to proceed from ordered to disordered states The entropy change for (system + surroundings) is unchanged in reversible processes and positive for irreversible processes All processes proceed toward equilibrium - i.e., minimum potential energy

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Entropy A measure of disorder An ordered state is low entropy A disordered state is high entropy dS reversible = dq/T
“What is Life?”, asked Erwin Schrödinger, in 1945. A disorganized array of letters possesses no information content and is a high entropy state, compared to the systematic array of letters in a sentence. Erwin Shrödinder’s term “negentropy” describes the negative entropy changes that confer organization and information content to living organisms. Shrödinger pointed out that organisms must “acquire negentropy” to sustain life.

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Energy dispersion Entropy can be defined as S = k ln W And ΔS = k ln W final – k ln W initial Where W final and W initial are the final and initial number of microstates of a system, and k is Boltzmann’s constant. Viewed in this way, entropy represents
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Chapter 3 - Reginald H Garrett Charles M Grisham Chapter 3...

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