BIOC520: Biological Chemistry 
			
L-13: Bioenergetics
							
J. Thomas
August 15, 1997

OBJECTIVES:
1.	To understand basic thermodynamics.
2.	To understand the concepts of standard free energy changes, actual
	free energy changes, and how they are related to the equilibrium for
	reactions.  
3.	To understand the key role of ATP in energy conversions, and how
	to identify other energy rich compounds.


I.	Energy producing and energy utilizing systems
	A.	Catabolic pathways - generation of energy by
		transformation (glycolysis) or oxidation (oxidative
		phosphorylation) of ingested or stored fuels.

	B.	Anabolic pathways - utilization of energy for
		biosynthetic purposes (DNA synthesis, protein synthesis,
		etc.)

         C.	ATP - the link between the two pathways (Fig. 6.2
		Devlin, p. 219)
		1.	Phosphoanhydride bonds as high energy bonds
		2.	Other nucleotides  (Fig. 6.3 Devlin, p. 219)
			a.	GTP: gluconeogenesis and protein synthesis
			b.	CTP: lipid synthesis
                     	c.	UTP: glycogen synthesis
			d.	All depend on ATP formation: nucleoside
				diphosphate kinase (Fig. 6.4 Devlin)
		3.	Other bonds having a high free energy of
			hydrolysis (> 7 kcal/mole)(Table 6.3 Devlin, p.223)
			a.	1,3 bis-phosphoglycerate (mixed acid
				anhydrides)
			b.	Phosphoenolpyruvate (enol phosphates)
			c.	Creatine phosphate (phosphoguanidines
			d.	Pyrophosphate (phosphoric acid anhydrides)
			e.	Acetyl CoA (thiol esters) (Fig. 6.11
				Devlin, p. 226)

II.	Thermodynamic relationships and energy rich compounds
	A.	Laws of thermodynamics
		1.	First Law: energy may be converted from one form
			to another, but the total in a system remains constant.
			 (Glucose --> lactate + ATP)
		2.	Second Law: Entropy (deltaS) is a measure of
			disorder or randomness of a system.  All systems
			tend to progress towards maximum entropy. Entropy
			is unavailable to perform useful work.
		3.	Free energy (deltaG): available for useful work
			a.	deltaG = deltaH - TdeltaS   (deltaH =
				enthalpy, T = temperature in degrees K) 
			b.	Exergonic:free energy lost,
				spontaneous reaction (deltaG less than 0)
			c.	Endergonic:requires energy for
				reaction to proceed
 				(deltaG greater than 0)
			d.	At deltaG = 0, the reaction is at
				equilibrium
			e.	The actual free energy change (deltaG for 
				a reaction is equal to the standard free
				energy (deltaGo’) plus a term tha depends
				on actual concentrations of products and 
				reactants
				deltaG’ =deltaGo’+ RTln{[Products]/[Reactants]}
				deltaG’= deltaGo + 1.4 logP/ (in kcal/mole)
				Where deltaGo’ = -Rtln(Keq
					     = -1.4 log(Keq) (inkcal/mole)
			f.	Free energy changes for coupled
				reactions are ADDITIVE
								deltaGo’ 
					A+ B --> C + D		 -5.0
					D --> P + Q              +4.5
		Sum of coupled rx     A + B ----> C + P + Q	 -0.5

				(See top of p. 225, Devlin for example)

	B.	Thermodynamics of membrane transport
		1.	Uncharged molecules: deltaGo’ = RT ln {[C2]/[C1]}
						= 1.4 log{[C2]/[C1]}
			where the direction of transport is from C1 to  C2 

		2.	Charged molecules: must also consider the membrane
			potential (inside negative generally) 
 			  deltaGo’ = RT ln {[C2]/[C1]} + Z(deltaPsi)  
				= 1.4 log {[C2]/[C1]} + 23Z(deltaPsi)  
			where F = Faraday constant = 23 kcal V-1mole-1
			deltaPsi= the membrane potential (in volts)
			and	Z = the charge on the ion

jt 9/96