Saturday, October 20, 2012

Chapter 5: Gibbs Free Energy



Chapter 5-Gibbs Free Energy
Problems: 5.1,3,5,11; concept:5.9,19,21,22,23

1.G-energy to drive chemical reactions
-ΔpG- tabulated (in table)
-ΔrxnG- usually calculated
eq.1: ΔrG- ∑v*ΔfGproducts –∑v*ΔfGreactants
-if 0, reaction is at equilibrium
-if negative, reactions proceeds towards right (spontaneous)
-if positive, reaction will not proceed (non-spontaneous)

2.Phase Transitions
-Phase 1 --> Phase 2:
eq.2:ΔrxnG= n* ΔfGphase 2 – n* ΔfGphase1 (ΔG is molar)
-if ΔGf phase 2 > phase 1, ΔGrxn is positive (non-spontaneous)
-if ΔGf phase 1 > phase 2, ΔGrxn is negative (spontaneous)
-if ΔGf phase 1 = phase 2, ΔGrxn is 0 (equilbrium)
-stable phase- phase with lowest ΔGf

3.Molar ΔGf vs Pressure- ΔGf,m or ΔGm = Vm*ΔP
-ΔG is directly proportional to changes in pressure
-larger molar volume- ΔG changes more as pressure changes for substances with larger molar volumes
eq.3:Vm=ΔG/ΔP
-solids,liquids: final ΔGm= ΔGm,i + Vm(Pf-Pi), where pressure is in bars
-gases: final ΔGm*(Pf)= ΔGm*(Pi)+RTln(Pf/Pi)
-reactions:  ΔGrxn= ∑V*ΔGm,final (products) – ∑V*ΔGm,final (reactants)

4.Molar ΔGf vs Temperature
-for small changes in T, entropy values are nearly constant
eq.4:ΔGm=-Sm*ΔT

5.Phase boundaries- on phase diagrams, show the pressure and temperature combinations at which 2+ phases are stable
-liquid-vapor boundary-liquid is in contact with and in equilbrium with a gas of that composition; pressure of the vapor is its vapor pressure, which substantially increases with temperature
-solid-vapor boundary-solid in contact with and in equilbrium with vapor; sublimination vapor pressure of the solid can be determined in the same way as the liquid vapor pressure
-slope- slope of boundary determined by thermodynamic properties

 6. Clapeyron equation- finds slope of boundary (ΔP/ΔT), ONLY fo small changes in P and T
-ΔtrsH- change of heat during transition between phases (where temperature and pressure stay constant)
eq.5: ΔP/ΔT=ΔtrsH/T*ΔtrsV

7.Clausius-Clapeyron equation: Δ(lnP)= ΔvapH/RT2 *ΔT
-liquid-gas boundaries
eq.6:lnP’=lnP+ΔvapH/R*(1/T-1/T’), where P’ is final P, and T’ is final T
-Table 5.1- log(P in kPa)=A-(B/T), where A and B are constants (see derivation on p.113)














8.Critical point-terminal point on liquid-gas boundary curve
-highest pressure at which liquid can be condensed
-fluid- above critical point, state of matter is called “fluid”, no boundary
-observed between states of matter as seen between liquid and gas













9.Normal boiling point- boiling temperature at 1 atm
-Standard boiling point- boiling temperature at 1 bar
-Normal boiling point- melting temperature at 1 atm
-Standard melting point- melting temperature at 1 bar

10. Phase Rule- for a system at equilbrium, F=C-P+2
-F=degrees of freedom, C=number of component, P=number of phases, 2=T+P
-components- minimum number of species necessary to define all the phases present in a system
-degrees of freedom- number of intensive variables (P,T,mol fraction, etc.) that can be changed without disturbing equilbrium
-triple point- F=0 (C=1, P=3)
-phase boundary- F=1 (C=1, P=2)


Monday, October 15, 2012

General Biochemistry 2: Lecture 10,11 (Photosynthesis, Photosystems, Cyclic)



LECTURE 10,11: PHOTOSYNTHESIS, REACTION CENTERS, PHOTOSYSTEMS

A. Photosynthesis- light driven synthesis of CH2O from CO₂; also produce oxygen by oxidating water; overall: CO₂ + 2 H₂O à CH₂O + O₂ + H₂O
Chloroplasts-site of photosynthesis; 1-1k chloroplast per cell, very in size/shape, usualy 5 um long ellipsoids.
-3 membranes: inner, outer, thylakoid membranes (where light driven reactions take place)
-3 regions: intermembrane space, stroma (dark reactions), thylakoid lumen
-thylakoid membrane- light reactions; invaginations of inner membrane cause these, resemble cristae
-thylakoid vesicle- arranged to have disk-like sacs (grana), stacked in piles, connected to each other by stroma lamellae.
-1 chloroplast=10-100 grana
-stroma-concentrated solution w enzymes, dna, rna, ribosomes

B. Reaction Centers
I. Light reactions (thylakoid membrane)- use light to generate nadph, atp and O₂. Resembles ET and OP in mitochondria.
1. Photosynthetic Reaction Center(RC)-primary photochemical rxns take place in RC.
-chlorophyll- green pigments that capture sunlight, located in and around photosystems embedded in thylakoid membrane of chloroplasts. Structure- porphyrin with magnesium at the center.
-Bacteriopheophytin- a bacteriochlorophyll where Mg2+ ion is replaced by 2 H⁺; Reaction center from a purple bacteria (rhodopseudomonas viridis) is a transmembrane protein with several chromophores (BchI a and b, nonheme Fe(II), Bpheo b, ubiquinone, menaquinone)
-antenna chlorophyll- chlorophylls not in RC;  don’t participate directly in photochemical reaction, but capture photons from sunlight.
2.Light Harvesting Complex B (antenna complex)- has several membrane-bound hydrophobic proteins, each with many chlorophylls and other pigments.
-carotenoid- accesory pigments; non-chlorophyll pigments that absorb wavelengths chlorophylls don’t strongly absorb.
-number of LHCs- many more LHCs than PRCs.
-lower energy state- light captured by antenna complex, transferred to series of antenna pigment molecules, eventually trapped by PRC (10E-10 seconds, >90% efficiency); PRC has lower excited energy state than antenna pigments.
-all O₂ cells- have psysI and II; non-O₂ cells only have psys I.

C.Photosystems
1.Photosystem 1-forms nadph
-max efficency at 700nm; absorbs 4 quanta, makes strong reductant, weak oxidant
-4[ P700 + q à P700* (strong reductant) à P700+ (weak oxidizer)+ e]
-4[ P700+ + e(from P680*) à P700]
-P700*- strong reductant provides 4e to reduce 2 NADP+ to 2 NADPH
-P700+ - weak oxidant recieves 4 e from weak reductant made by psys II to regenerate ground state psys I P700
- ferridoxin-nadp+ reductase-forms nadph in stroma

2.Photosystem II-forms O2 by oxygen-evolving center (OEC)
-max efficiency drops at >680nm; absorbs 4 q, makes weak reductant and strong oxidant
-4 [P680 + q à P680* (weak reducer) à P680+ (strong oxidant) + e]
-4 [P680+ + e (from water) à P680]
-P680+ -strong oxidant takes 4 e from 2water to make 4H+ and O2
-P680*- weak reductant provides 4 e to weak oxidant formed by psysI

3.H⁺ gradient- drives atp synthesis by atp synthase; similar to OP
-thylakoid lumen- 4e goes from weak reducer P680* to weak oxidant P700+, coupled to pumping of 8 H⁺ into thylakoud lumen.
-Evolution of one O₂- from 2 waters produces 4H+ in thylakoid lumen.
-redox-active factors- chlorophylls, cytochromes, Q, FeS clusters, plastocyanin help transfer 4e between photosystems.
-plastocyanin- peripheral membrane protein on thylakoid luminal surface, cycles between CuI and CuII, a redox-active factor.

4.cyclic transport- produces atp, but no nadph or O₂
-involves only photosystem I;
-allows cells to adjust ATP:NADPH ratio
-regulation unknown

5.efficiency of non-cyclic ET: 1.25 ATP/quantum (10 atp/8 quanta)
-for every O₂ made or 8 quanta absorbed
-water evolution: 4H+ made in lumen from 2H2Oà4H+ + O₂ 
-4e from PSII to PSI: 8H+ pumped into lumen
-H⁺ gradient: 12 H⁺/3 H⁺ to power synthase= 4 ATP
-PSI’s p700*: makes 2 NADPH, 3 atp/nadph, equals 6 ATP

6.efficency of cyclic ET: 0.67 ATP/quanta
-for every 4 q absorbed by PSI, 8H+ pumped into lumen, (8H+/3H+ to power synthase)/4 quanta
Dark reactions- use nadph and atp to make ch2o from water and CO₂. in eukaryotes, happens in stroma.

General Biochemistry 2: Lecture 9 (ATP Synthesis)



LECTURE 9: ATP SYNTHESIS

Energy coupling- free energy released by electron transport must be saved in a form that atp synthase can use.
chemiosmotic theory (1961, peter mitchell)- ETàcoupled to pumping of H⁺ from mitochondria matrix across inner membrane to outside à create H⁺ electrochemical potential gradient across inner membrane à this gradient is energy source which drives atp synthesis
-inner membrane permeability- requires intact inner membrane, impermeable to ions like H⁺, OH-, K+, Cl- (permeable to CO₂, O₂, H₂O)
-electrochemical gradient- ET = H⁺ transport from matrix to outside, creating big gradient across inner membrane
-Potential = 0.168 V (more negative inside);
-pH of matrix = 0.75 units higher than intermembrane space,
-ΔG(transport H⁺ outside) = 21.5kJ/mol
-2,4dinitrophenol (DNP)- compounds that increase permeability of inner membrane to H⁺ allow ET to proceed, but inhibit ATP synthesis. Thus, oxidation (or ET) and phosphorylation can be uncoupled by uncouplers like 2,4-dintrophenol (DNP)
p/o ratio- ratio of atp synthesized to oxygen reduced
p/2e ratio-ratio of atp synthesized to 2-e reduction of some e⁻ acceptor other than o
-FADH₂/O₂(no agent or amytal)=2, (w CN- or DNP)=0
-FADH₂/Fe(w CN-)-3 (no agent or CN-)=1
-NADH/O₂(w CN-)=0
-NADH/Fe(CN6)-3=2
-pH gradient- atp is made by mitochondria/chloroplast when pH gradient artifically generated without ET.
-bacteriorhodopsin-purple membrane protein from halobacteria; pumps H⁺ when illuminated; synthetic lipid vesicles w BR and beef heart mitochondrial ATPase can make ATP when illuminated.
-asymmetric orientation- NADH-Q reductase, Q-Cyt c reductase, Cyt c, cyt c oxidase, ATP synthase all asymmetrically oritented (used mitoc/submitoc particles w inner membrane inside out)
-Efraim Racker- discovered F0 and F1
1.F1- water soluble, peripheral membrane protein; atp hydrolysis in isolated soluble form
-a3b3yE, active in atp synthesis in synthase assembly
2.F0-water insoluble, transmembrane protein; forms proton channel.
-a1b2c9-12 in e. coli, and some addition subunits in mitochondrial F0
3. Binding Change Mechanism- shape change takes place when T has ATP and L has ADP,Pi
-L,O,T(atp)àL(adp,p),O,T(atp) + energyà L,O(ATP),T(adp,p) + ATP,waterà L,O,T(atp)
-shape change takes place when T site has ATP and L site has ADP,Pi; results in conversion of LàT, TàO, OàL;
-shape change requires energy, transmiited to catalytic α3β3 assembly via ye assembly.
-atp synthesize at new t site, original atp released from new o site

General Biochemistry 2: Lecture 8 (Electron Transport Chain, Complexes, Inhibitors)



LECTURE 8: ELECTRON TRANSPORT CHAIN, COMPLEXES, INHIBITORS

A. NADH oxidation- is highly exergonic- -218 kJ/mol
-NAD⁺ + H⁺ + 2e à NADH (-.315 V)
-oxygen + 2H+ + 2e à water (0.815 V)
Overall: oxygen + NADH + H⁺à water + NAD⁺
ATPàADP: -30.5 kJ/mol
ATPàAMP: -32.2 kJ/mol
2. Efficiency of ATP Synthesis- (3 ATP per NADH) ÷ (total energy per NADH) = 42%
-70% in mitochondria

B. ET Carriers- NADH; FMN; Q; FeS; Cyt a+a3,bl+bh,c,c1; Cua; Cub; O₂
1.Hydrogen carriers- FMN; NAD⁺; Q;
-FMN- add 2H⁺ and 2e, get FMNH2. (1H and 1 e= FMNH*)
-NAD+ - add 2H+ and 2e, get NADH + H⁺.
-Q- add 2H+ and 2e, get QH2.
2. Electron carriers- FeS, cytochromes (ET heme proteins), Cu proteins
-Fe3+ à Fe2+
-Cu2+àCu+

C. Complexes that make up ET chain
1. Complex I- NADH-CoenzQ Oxidoreductase;
-NADH à [[[FMN à2 FeS]]]à Q (passes 2e from NADH to Q)
-inside: 8-9 iron-sulfur clusters and 1 FMN
-4H+ go outside
-possible mechanism: differential H⁺ binding and release caused by protein shape change; H bonded groups in proteins and water are like a proton wire.
AH+BàA+BH. Proton moves from AH to B.
-bacteriorhodopsin-model for proton pump through proton wire
a.Cycle 1- QH₂ + Cyt c1 (Fe3+) à Q*- + Cyt c1(Fe2+) + 2H+ (cystol)
-QH2 from complex 1; pump 2H+ to intermembrane space, then to cytosol;
-donate 1e to ISP, which goes to c1;
-makes 1 Q-*
b.Cycle 2- QH₂ + Q-* + Cytc1(Fe3+) + 2H⁺(mito) à Q + QH₂+Cytc1(Fe2+)
-obtain QH₂ from complex I; pump 2H⁺ to cyto;
-Donate 1e to ISP, goes to c1. Take up 2 H⁺ from mito.
-Generate 1 QH₂, not net gain or loss of QH₂.
Net: QH₂ + 2 Cytc1(Fe3+) + 2H⁺ (mitochondria) à Q + 2 Cytc1(Fe2+) + 4 H⁺ (cystol)
-4 H⁺ pumped out, 2 c1 reduced, use 2 H⁺ from matrix.

2.Complex II- Succinate-CoenzQ Oxidoreductase
-Succinateà[[[FAD (succinate DH, 2H+ released)à3 iron-sulfur clusters à Cyt b560]]]à Q
-I and II not in series
-inside: 3 FeS clusters, succinate dehydrogenase FAD, and cyt b560
-2H+ go outside
3.Complex III- CoenzQ-Cytochrome C Oxidoreductase
-QH2à[[[CytB or FeSàCyt c1]]]à Cyt c
-inside: 2 Cyt b (bL for low and bH for high potential), 1 Cyt c1, and 1 Fe-S cluster.
-4H+ go outside, 2H+ inside
4. Complex IV- Cytochrome c oxidase
-2 Cytc(Fe2+) + 2H⁺ + .5O₂ à[[[CuAàCytaàCyta3-CuB]]]à 2 Cytc(Fe3+) + H₂O
-has cyt a, cyt a3, cua, vub
-high potential- (CuA-Cyta) lower potential than (Cyta3-CuB)
-2H⁺ go to cytosol
- Cyt c- between III and IV. Loosely bound to outer surface of inner membrane. Shuttles e⁻ between Cyt c1 and cyt c oxidase.

D. Donaters/Acceptors
1.Physio e⁻ donating systems:
-β-hydroxybutyrate dehydrogenase- β-HOButyr+NAD⁺àAcetoacetate+NADH
-Succinate DH- Succinate+FADàFumarate+FADH₂
2. Artifical e⁻ donating systems: ascorbateàtetramethyl-p-phenylenediamine (TMPD)àCyt C
3. Physio e⁻ acceptor: O₂ as acceptor of e from Complex IV
4. Artifical e⁻ acceptor: Fe(CN6)3- accepts e from Cyt cred

E. ΔG=-nFΔE, where F=96494 J/mol*V
1.Site 1(Complex 1)- ΔG=-69.5, ΔE=.36V
-NADH+H⁺+QàNAD⁺+QH₂
-reduce NAD=-.315V; reduce Q=.045V
2.Complex II- no phosphorylation
-FADH₂+QàFAD+QH₂
-ΔE=.085 V, ΔG=-16.4 kJ/mol
3.Site 2 (Complex III)- ΔG=-36.7 kJ/mol, ΔE=0.19V
-QH₂+2CytcoxàQ+2Cytcred
4.Site 3 (Complex IV)- ΔG=-112kJ; ΔE=.58V;
-2CytRED+ 2H⁺+ .5O₂à2CytOX+ H₂O

F.Inhibtors
Rotenone and Amytal- block complex I
Antimycin A- blocks complex III
CN- -blocks complex IV

G.P/O value- ratio of ATP made over oxygens used
- β-HOButyr/NADH and O₂= 3
- Succinate/FADH₂ and O₂= 2
- β-HOButyr/NADH and Fe(CN6)-3= 2
- Succinate/FADH₂ and Fe(CN6)-3= 1
- ascorbate and O₂= 1
-phosphorylation and oxidation tightly coupled, NADH+P+O₂ wont happen until ADP is added.
-Reconsitution- isolated components and phospholipid vesicles remake active sites.