electron transport chain/system
DESCRIPTION
ELECTRON TRANSPORT CHAIN/SYSTEM. BIOT 309 Fall 2013. Electron transport chains are the cellular mechanisms used for extracting energy from sunlight in photosynthesis and also from redox reactions, such as the oxidation of sugars (respiration). - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/1.jpg)
ELECTRON TRANSPORT CHAIN/SYSTEM
BIOT 309Fall 2013
![Page 2: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/2.jpg)
• Electron transport chains are the cellular mechanisms used for extracting energy from sunlight in photosynthesis and also from redox reactions, such as the oxidation of sugars (respiration).
• The electron transport chain consists of a spatially separated series of redox reactions in which electrons are transferred from a donor molecule to an acceptor molecule. The underlying force driving these reactions is the Gibbs free energy of the reactants and products. The Gibbs free energy is the energy available ("free") to do work. Any reaction that decreases the overall Gibbs free energy of a system is thermodynamically spontaneous.
![Page 3: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/3.jpg)
Note that electrons can enter the chain at three levels: at the level of a dehydrogenase, at the level of the quinone pool, or at the level of a mobile cytochrome electron carrier. These levels correspond to successively more positive redox potentials, or to successively decreased potential differences relative to the terminal electron acceptor. In other words, they correspond to successively smaller Gibbs free energy changes for the overall redox reaction Donor → Acceptor.Individual bacteria use multiple electron transport chains, often simultaneously. Bacteria can use a number of different electron donors, a number of different dehydrogenases, a number of different oxidases and reductases, and a number of different electron acceptors. For example, E. coli (when growing aerobically using glucose as an energy source) uses two different NADH dehydrogenases and two different quinol oxidases, for a total of four different electron transport chains operating simultaneously.
![Page 4: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/4.jpg)
ELECTRON TRANSPORT CHAIN/SYSTEM
• In bacterial membrane b/c– Allows charge separation– Stabilizes exact conformation
• Responsible for:– Extruding protons and establishing proton motive force
(pmf) across membrane (proton pump)– Removing electrons from substrates (NADH, FADH2, etc.)– Transferring electrons down a series of electron carriers
to final electron acceptor, e.g., O2 during aerobic respiration
• Not responsible for: generation of ATP; membrane bound ATP synthase does this
![Page 5: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/5.jpg)
• Although NADH is the most important electron donor in eukaryotes, bacteria can use a number of different electron donors, a number of different dehydrogenases, a number of different oxidases and reductases, and a number of different electron acceptors.
![Page 6: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/6.jpg)
ETC COMPONENTS
• Multi-subunit protein complexes join with electron carrier molecules
• 1 or more electron carrier molecules associate with protein complexes depending on protein components
• Depends on species, environmental conditions, even temperature
![Page 7: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/7.jpg)
ETC COMPONENTS
• Major classes of electron carrier types that undergo redox are:– Flavoproteins– Quinones – Iron-Sulfur proteins– Cytochromes
![Page 8: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/8.jpg)
ETC/S GENERAL STRUCTURE1. Dehydrogenase –> Quinones –> cytochromes (aerobic)
2. Dehydrogenase –> Quinones –> reductases (anaerobic)
• Characteristics: Branched, modular, inducible– Multiple types of each => flexibility – Branches occur at quinones and cytochromes
• Differ in Δ p generation b/c # coupling sites differ • Differ in final acceptor, e.g., oxygen, affinity
• Bacterial ETC: species may use > 1 ETC b/c– More diverse– Genomes allow picking of system to suit environment, e.g., different
carriers, different proteins– Different carbon sources– Different electron acceptors and donors
![Page 9: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/9.jpg)
PRINCIPLE FOR ELECTRON MOVEMENT
• E- move from high potential electron carriers to low potential electron carriers; each step involves redox reaction
![Page 10: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/10.jpg)
ELECTRON TRANSPORT CHAINOF PROKARYOTES (AEROBIC)
simple example
![Page 11: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/11.jpg)
MORE COMPLEX ARRANGEMENT IN SOME BACTERIA
Question 1: How many H+ move outside per ETC component?Question 2: Are these integral or peripheral proteins?
• H+ moves outside membrane (proton motive force)• Electrons passed from one electron carrier to another• Not all extrude H+
![Page 12: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/12.jpg)
![Page 13: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/13.jpg)
ETC OVERALL ATP PRODUCTION
NADH + H+ + ½ O2+ 3ADP + 3 Pi —> NAD+ + 3ATP + 4 H20
NADH yields 3 ATP
[FADH2 ] + ½ O2+ 2ADP + 2 Pi —> [FAD]+ + 2ATP + 3 H20
FADH2 yields 2ATP
![Page 14: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/14.jpg)
FLAVOPROTEIN ELECTRON CARRIERS
• Large enzyme complexes with flavins (FAD, FMN) as e-
carrier• Named after electron donor, e.g., NADH
dehydrogenase• Accept electrons from many sources: NADH,
succinate• Pump protons (not in all bacteria) to periplasm• Funnel electrons to quinones• Associated with many different proteins -> different
redox capabilities (potential) • Synthesized when needed, i.e., inducible
![Page 15: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/15.jpg)
E. coli (glucose, aerobic) ETC
• USES TWO– NADH dehydrogenases– different quinol oxidases
• CARRIERS COMBINE INDEPENDENTLY
• FOR A TOTAL OF FOUR DIFFERENT ETCS OPERATING SIMULTANEOUSLY
![Page 16: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/16.jpg)
FLAVOPROTEINS STRUCTURES: RF, FMN, and FAD
CH3
CH3
CH3 is terminal methyl group
Adenine
WHAT IS RIBOFLAVIN, other than a part of this molecule?
![Page 17: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/17.jpg)
REDOX OCCURS AT N1 and N5 on riboflavin molecule
OXIDATION AND REDUCTIONFAD, FMN
![Page 18: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/18.jpg)
ETC: QUINONE ELECTRON CARRIERS• Mediators of electron transfer between different protein complexes in biological
membranes• mobile carriers of electrons in membranes, but • some tightly associated with protein molecules to function in intramolecular
electron transfer Example = NDH-1-type dehydrogenases (NDH-1)
functioning as NADH:MK oxidoreductase• Lipids, lipid soluble• Can be highly mobile• Carry H+ and e-
• side chains of varying lengths and differing saturation(-CH2-CH=C(CH3)-CH2-)n
• Head groups can also vary• Ubiquinone and menaquinone
– UQ (Coenzyme Q) – aerobic and nitrate respiration, mostly G-– MQ (structure related to vitamin K) – fumarate respiration, mostly G+, anaerobic G-, not in
humans• Responsible for Q-cycle
![Page 19: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/19.jpg)
OXIDIZED AND REDUCED FORMS
Number of isoprenoid units( R) depends on species(-CH2-CH=C(CH3)-CH2-)n
Head Group
![Page 20: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/20.jpg)
QUINONE ELECTRON CARRIERS
• Used by E. coli as terminal e- acceptor – E. coli does not have a cytochrome oxidase
or a bc1 complex• Two different terminal quinol oxidases (both proton
pumps) reduce oxygen to water
![Page 21: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/21.jpg)
ETC: IRON-SULFUR PROTEIN ELECTRON CARRIERS
• Non-heme iron and acid-labile sulfur - at biological pH the sulfur is bound to the iron
• Non-heme iron bound to cysteine sulfur of a protein
• Several iron sulfur clusters – Different Eh values
– Proteins can have more than one Fe-S cluster– e- move around among them
![Page 22: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/22.jpg)
ETC: IRON – SULFUR PROTEINS ELECTRON CARRIERS
• Redox rxns in membrane (cytoplasm = non-ETC)
• Non-heme iron bound to: – Sulfur of cysteine on protein (#)– “acid-labile” sulfur * (sulfide)
*
*
#
#
LINEAR2F - 2S CUBANE
4F - 4SSEVERAL DIFFERENT Fe-S CLUSTERS
![Page 23: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/23.jpg)
ETC: IRON-SULFUR PROTEIN ELECTRON CARRIERS
• Proteins can have more than one Fe-S cluster• Common bacterial clusters
– F4-S4
– 2(F4-S4) – >2(F4-S4)
• Variations at cys– Pyrococcus furiosus: Fe4S4, one of conserved Cys
is substituted with aspartic acid– Loss of 4th cys also produces F3-S4
![Page 24: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/24.jpg)
ETC: IRON-SULFUR PROTEIN ELECTRON CARRIERS
• Protein structure determines if redox is: -1 -2 or
-2 -3 (MW 6,000-9,0000)
(Fe4S4*S4CYs)2- (Fe4S4*S4CYS)3-
• Standard redox potentials do not apply b/c located within protein
• Actual redox potential depends on protein• oxidoreductases
![Page 25: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/25.jpg)
ETC: CYTOCHROME ELECTRON CARRIERS
• Heme (non-heme Fe (NH-Fe)) = redox prosthetic group in proteins
Fe 2+ Fe3+
• Have 4 pyrroles attached by methylene bridges• Pyrrole N linked with Fe • Different classes based on side chains of pyrrole
rings- Different heme types in bacteria: a, b, c, d, o- Iron has redox capacity
![Page 26: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/26.jpg)
TETRAPYRROLE/PORPHRYIN
Tetrapyrrole or porphryin
methylenepyrrole
![Page 27: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/27.jpg)
ETC: CYTOCHROME ELECTRON CARRIERS
• Different functions– Move 1 electron/heme– Most also act as proton pumps– Some are terminal oxidases and reductases in ETC, i.e., transfer to
terminal acceptor
EXAMPLE4 Fe2+-cytochrome c + 8 H+
in + O2 → 4 Fe3+-cytochrome c + 2 H2O + 4 H+out
• Hemoproteins– Integral membrane proteins– Often have > 1 heme in a protein– Single or multiple subunits of protein
• Entry point for electrons from inorganic e- donors: nitrite, ferrous ion, etc.
![Page 28: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/28.jpg)
STRUCTURES: DIFFERENT HEMES
Heme aCytochrome 3 oxidase
Non-covalent bond to protein
Heme bCytochromes b
Non-covalent bond to protein
*
pyrrole
*
![Page 29: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/29.jpg)
STRUCTURES: DIFFERENT HEMES
Heme cCytochromes cCovalent bond
to protein
Heme oCytochromes o
Non-covalent bond to protein
![Page 30: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/30.jpg)
DIFFERENT HEMES
Heme d1
Occurs with cytochrome c -> cytochrome cd1
nitrate reductase
Heme dCytochromes d
Non-covalent bond to protein
![Page 31: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/31.jpg)
BACTERIA: DIFFERENT CYTOCHROMES C
aa3 type: P. dentrificans, Rb. Sphaeroidesb3 type: Thermus thermophilus
bo3 type: E. coliba3 type: Acetobacter acetiaa3 type: B. subtilis
![Page 32: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/32.jpg)
TERMINAL ELECTRON ACCEPTORS
• Inorganic and organic molecules• Inducible• Two general types
– Aerobic uses OXIDASES: oxygen– Anaerobic uses REDUCTASES: fumarate, nitrate,
nitrate
![Page 33: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/33.jpg)
TERMINAL OXIDASE VARIATIONS
• Cytochrome oxidases: a, aa3, b, d, o and combinations thereof, e.g., bd, cbb3
– Differ in:• affinities for oxygen • types of hemes or metals• ability to work as proton pumps
• Quinol oxidases
![Page 34: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/34.jpg)
ETC
• Coupling sites:– Redox reactions coupled to H+ extrusion– Occur at dehydrogenase and oxidase complexes
quinone shuttles electrons but does not perform redox
![Page 35: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/35.jpg)
ETC in DIFFERENT BACTERIA
• See White, Chapter 4.7 for ETC of different bacteria
• See Figure 4.14, 4.15, 4.16
• E. coli is summarized next
![Page 36: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/36.jpg)
SUMMARY: E. coli ETC
• NADH dehydrogenase– NDH-1, coupling site; 4 H+/e- – NDH-2, not a coupling site no proton
movement, only e- transfer• 3 quinones – ETC branches here
– Type and % varies with e- acceptor(s) in use and [O2]– Aerobic: UQ = 60%, MQ = 3%, DMQ = 37%– Anaerobic: grow on nitrate – DMQ = 70%, MQ = 30%– Anaerobic: fumarate – MQ = 74%, DMQ = 16%, UQ =
rest
.
..
![Page 37: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/37.jpg)
E. coli ETC• 2 quinol oxidases = terminal oxidases Aerobic characteristics• Quinol oxidation movement of 1 proton
across membranes • cytochrome bd: = proton pump
– b/c of Qox H+ moves outside – Operates at low O2 tension = high O2 affinity
• cytochrome bo: = proton pump– 1H+/e- + 1 H+ from Qox
– Operates at high O2 tension = low O2 affinity
![Page 38: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/38.jpg)
EMP THROUGH ETC
FLOW OF
ELECTRONS AND
ATP PRODUCTION
![Page 39: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/39.jpg)
http://vcell.ndsu.nodak.edu/animations/etc/movie.htm
![Page 40: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/40.jpg)
![Page 41: ELECTRON TRANSPORT CHAIN/SYSTEM](https://reader033.vdocument.in/reader033/viewer/2022061423/568159ef550346895dc737c7/html5/thumbnails/41.jpg)