Bioenergetics

Question 1

Organic H+ carriers

Answer 1

NADH
Flavoproteins via FADH - non-mobile
Quinones - hydrophobic
Tyrosine - loses H+ and e- generating an O. radicak

Question 2

Metal e carriers

Answer 2

FeS clusters (Fe, 2Fe2S, 4Fe4S). Fe co-ordinated by Cys, but Rieske is 2fe2s with one Fe co-ordinated by two His residues

Cytochrome - haem cofactor uses iron, porphyrin ring co-ordinates Fe

Chlorophyll - Mg, co-ordinated by porphyrin

Plastocyanin, Cyt oxidase - Cu

OEC - Mn

Question 3

Complex I

Answer 3

L-shaped. Pumps 4H+ for every 2e- transported by NADH

NADH –> FMN –> 8xFeS –> Q –> QH2

Question 4

Complex II

Answer 4

Succinate –> FUmurate
No pumping of H+
FAD –> FADH2 –> 3xFeS –> Q –> QH2

Question 5

Complex III

Answer 5

Q cycle
QH2 binds to o site
1e –> Rieske ISP, rotates –> cytc1 –> cyt c
1e –> bL heme –> bH heme –> Q in ‘i’ site

Second round reduces QH to QH2 in i site

Question 6

Complex IV

Answer 6

Cyt c –> Cu2+ of CuA in subunit II –> heme a in subunit I –> binuclear centre of subunit 1. When both CuB and heme a3 are reduced –> O2 binds heme a3, reduces to H2O

Pumps 4H+ for every O2 –> 2H2O

Question 7

Paracoccus ETC

Answer 7

2 paths of e- flow from QH2:
forward e- flow –> ATP synthesis via H+ gradient
Reverse e- flow –> NADPH, reducing power.

Question 8

Light harvesting in cyanobacteria

Answer 8

Phycobilisome - many pigments absorbing different wavelengths (phycoerythrin, phycocyanin), energy transferred unidirectionally to chlorophyll in the RC via RET

Question 9

Light harvesting in purple bacteria

Answer 9

LH2 consists of concentric ring of 9a and 9b subunits, with bacteriochlorophyll molecules B800, B850. LH1 has similar concentric rings of a and b subunits with a RC complex in the centre that has a quinone-binding site.

RET from LH2 B800, B850 to LH1 B870 to RC special pair B870

Question 10

Light harvesting in thylakoids of higher plants

Answer 10

LHCs associate with RC - increase light harvesting efficiency using antenna chlorophylls, passes energy using RET
Also contains carotenoids,conferring photoprotection

LHC-I binds to PSI, LHC-II binds to both PSI and PSII

Accumulation of PQH2 activates protein kinase that phosphorylates LHC-II, causes dissociation of LHC-II from PSII to PSI

Question 11

ETC in purple bacteria

Answer 11

Cyclic, non-oxygenic

Bac-Chl* –> Pheophytin –> Qa –> Qb –> Q pool –> Cyt bc1 –> Cyt c2 –> Bac-Chl (Cyclic photophosphorylation) OR Cyt c oxidase (OXPHOS)

Question 12

ETC in chloroplasts and cyanobacteria

Answer 12

PSII LHC excitation RET –> P680 (replaced by OEC–>Tyrz –>P680) –> ChlD1 –> Pheo –> PQa –> Fe –> PQB

PQB-H2–> Cyt b6f –> FeS –> PC
PC –> P700 –> Chl-A0 –> Chl-A1 –> Phylloquinone –> FeS –> Fd

Question 13

Fates of reduced ferredoxin

Answer 13

FNR –> NADPH

Nitrite reductase –> Nitrogen assimilation

Glutamate synthase

FQR –> QH2; generates more ATP, less NADPH

Question 14

2 models of how H+ pumping coupling to ETC

Answer 14

Redox loop model - on the same molecule
Eg. Q-cycle in complex III, quinones

Proton pump model - conformation changes in a transmembrane complex
Eg. Complex I

Complex IV has elements of both

Question 15

ANT/phosphate translocase

Answer 15

ANT: uses pmf, exports ATP, imports ATP, rocking sausage model, C-to-M transition

Phosphate translocase - symport of H+ and Pi

Question 16

ATP synthase structure

Answer 16

F0 = 1a2b8-15c, integral membrane complex - CryoEM
F1 = a3b3gde, bound to F0 on matrix facing surface - X-ray crystal structure

Question 17

Binding-change mechanism

Answer 17

18O-labelled H2O - reversible ATP hydrolysis, incorporates 18O into Pi.
Tightly-bound ATP - means deltaG for ATP hydrolysis is close to 0, but energy is needed to release ATP