Couples Reactions and Metabolic Pathways

set of principles that apply to all physical and biological processes and govern conditions under which they can occur

total amount of energy within a system and its surroundings is constant

total entropy (level of disorder) of a system and its surroundings always increases

entropy of a system approaches a constant value when its temp reaches 0

whatever part of the universe we are interested in closed system- cannot exchange matter across boundaries open system- can pass matter back and forth across boundaries (cells) surroundings- everything that surrounds the system (rest of universe)

enthalpy (H) = E + PV energy at constant pressure and volume thermodynamic quantity equivalent to the total heat content of a system It is equal to the internal energy of the system plus the product of pressure and volume. ∆H and ∆E are similar in solid and liquid heat released or absorbed by a system at constant volume is equal to total internal energy exo- release of heat (energy) endo- heat (energy) absorbed

refers to level of disorder in a system how energy is distributed in a system low entropy- organised high entropy- disorganised entropy always increases spontaneously

tells us if a process will occur on its own (spontaneous or not) expressed as ∆G ∆ G° = ∆H - T ∆S G considers for both enthalpy and entropy ∆G < 0 = a spontaneous process (exergonic) ∆G > 0 = not a spontaneous process (endergonic) all biochemical reactions must result in a loss of free energy/increased entropy and therefore be exergonic (- ΔG).

enthalpy- exothermic= ∆H < 0 endothermic= ∆H > 0 entropy- disordered= ∆S > 0 ordered= ∆S < 0 exothermic + disorded= -∆G (neg) spontaneous endothermic + disorded- spontaneous at high temp exothermic + ordered- spontaneous at low temp endothermic + ordered= +∆G- non spotaneous

low entropy (organised) to high entropy (disorganised) occurs when ∆S >0 (increased) high enthalpy to low enthalpy ∆H <0 (has decreased eg exothermic) example is bomb going off ∆G < 0 LOSS OF FREE (AVAILABLE) ENERGY

reaction will occur spontaneously if ∆G <0 reaction cannot occur spontaneosly if ∆G>0- energy input is required ∆G=0 at equilibrium ∆G reaction depends on free energy of the reactions and products and is independent f the path it takes to get there ∆G provides no info about rate of reaction

reaction cannot occur spotnaneously if ∆G is >0- energy input is required overall free energy change ∆G for a coupled reaction is equal to the sum of its individual reactions

energetically favourable- free energy of Y is greater than that of X during reaction of Y to X free energy (∆G) is <0 and disorder of universe increases spontaneous energetically unfavourable reaction of X to Y free energy (∆G) is >0 and universe would become more ordered only occurs if coupled with energetically favourable reaction

if ∆G is >0 energy must be stored eg after being released from oxidation stored in molecules called activated carriers as chemical group or electrons energy is then used for endergonic reactions or other cell activities ATP is most widely used and important activated carrier molecules

cells obtain energy through the oxidation of organic molecules energy is stored in covalent bonds of these organic molecules individual anabolic and catabolic reactions which enable us to obtain energy from organic molcules is called metabolism

oxidation- removal/ loss of electrons reduction- gain of electrons electrons are never actually lost- one molecule oxidised, another must be reduced (electrons are normally followed by hydrogen- less C-H bonds indicated oxidation)

oxidation of sugars consists of 10 reactions atp hydrolysed in reactions 1 and 3; phosphorylates sugar, couple reaction to make it energetically favourable glycolysis doesnt involved oxygen (involved oxidation + NAD is reduced) atp is generated in reaction 7 and 10 (energy investment phase - 1+ 3 and energy generation phase 7+ 10)

glycolysis may become 11 reaction pathway when lactate is produced from pyruvate when no o2 is available to act as electron acceptor, nadh passes electrons to pyruvate to form lactate normal circumstances- pyruvate moves into mitochondria where it is decarboxylated to form acetyl coA

fatty acids converted to fatty acyl coA and transported to mitochondria fatty acyl coA enters β-Oxidation β-Oxidation = 4 enzymatic reactions which reduces number of carbons on fatty acyl coA produces acetyl coA, 1xNADH and 1 FADH2 cycle continues until all carbons are removed and fatty acid is degraded

results in complete oxidation of c atoms on acetyl coA acetyl coA (2C) is transferred to 4C oxaloacetate to form citric acid (6C) series of 8 reactions (4 oxidation) regenerate oxaloacetate energy released - 3x NADH, 1xFADH2, 1XGTP