Electron Transport Chain

Question 1

Complex I: NADH Dehydragneous

Answer 1

• occurs in inner mitchondrial membrane
• NADH/FADH2 from the CAC
• Series of spontaneous e- transfer
• FAD/FMN
  FMN = FAD w/o nucleotide bound (AMP); recieves 2 e-
  FAD is bound to AMP
• Flavoprotein is any protein w/ FAD/FMN as prosthetic group.
  Complex I has a FMN, so it’s a flavoprotein.
• Iron clusters = multiple silfur inorganics or form cysteine together.
  Each Fe = 1 e-
  Fe 3+ to Fe 2+; However there are mutiple Fe in a cluster.
• Proteins will be pumped into inner membrane space.
• NADH matrix: e- = Complex I = Coenzyme Q = Complex III = Complex IV = O2 (pumps H+ = 10)
• Q will pick up e- and take to Complex III one e- at a time.

Question 2

Complex II: Succinate Dehydrogenous

Answer 2

• (FAD-E) Succinate to Fumerate + (FADH2-E) + Q to QH2 + (E-FAD)
• NADH that was created in the mitrochondrial matrix will max H+ pumping (Complex I) = H+ pumping 1,3,4
  More proton in mitchondrial matrix; more that will return.
  NADH matrix yeilds = 2.5 ATP’s, so 8 protons (3 H+/ATP)
• If Q picks up e- from Complex II and goes through ETC, it bypass Complex I = NO H+ pumping. Only H+ pumping Complex III and IV.
  FADH2 (CAC 2) yeilds = 1.5 ATP’s, so 5 protons (3 H+/ATP)
• Gradient: different concnetrations on either side of the membrane.
• Electrochemical Gradient
  Electro; changes are different on either side.
  Chemical; concentration of molecules is different on either side.
  Potential; difference in energy.
  pH is different by 1.4 units.

Question 3

Coenzyme Q

Answer 3

• Retrieves e- from Complex I, II, G3PDH and delivers to Complex III.
• Only delivers e- to Complex III b/c it has a system to funnel electrons one at a time through the ETC.
• Q (ubiquinone) = Q (semiquinone radical) = QH2 (ubiqionol)
• Q cycle: delivering one e- at a time to Complex III
  There is no proton pumping into the inner membrane space, once Q puts e- into Fe/S clusters.
  Q hydrophobic tail prevents it from leaving.
  One e- to Cytochrome C, and one e- will wait at Q.
  E- that go to Q, will go to Heme (BH/BL).
• Q is a free floater, but Cyt C cannot move; which is the reason Complex III/IV are together and are made on the same DNA strand.
• Exercise: less O2, but more Coenzyme Q.
  Q’s can retrieve e- and deliver to Complex III. More Q’s = more e- loaded and Catabolism (St3) w/o O2.

Question 4

Complex III: Cytochrome C

Answer 4

• Has heme as a prosthetic group.
  “cytochrome” = any protein w/ heme as a prosthetic group; which would include hemoglobin, Complex III/IV.
  It absorbs light at different wavelengths if oxidized/reduced.
• Types of Heme: a,b,c
  Heme b1 = 1st heme found in ETC.
  Heme c2 = 2nd heme found in ETC.
  Heme a3 = 3rd. heme found in ETC.
• Cytochrome C (Complex III)
  When heme is reduced at Fe2+
  Lysine indicates e- are in cytochrome C; + charges crowd around and attract to Complex IV - charges.
  After e- move to Complex IV, Fe3+ returns to Complex III.

Question 5

Complex IV

Answer 5

• When first e- arrives: delivered by reduced Cyto-C = Cu A = Heme A = Heme B = Cu B.
• When second e- arrives: delivered by reduced Cyto-C = Cu A = Heme A = Heme A3 (Fe2+).
• O2 retrieves e- from ETC.
  O2 takes off e- via a peroxide bridge.
  Then, 2e-/2 H+ to come inside = 2e- yeild Cu-OH/Fe-OH and 2H+ yeild 2 H20 moelcules and Cu2+/Fe3+.
• Sometimes we get O2 radical
  Dangerous oxygen radical enzyme to fix = superoxide dismutase (SDM)
  = Mutase takes FG in one molecule to another.
  = “dismutase” means it’ll break the molecule into two pieces.
  = means it’s catalytically perfect (kcat/km =10^7)
  = “scavenger enzymes”
  If you have 2 O2 radicals + 2H+ = SDM = O2 + H2O2 = catalase = H20 + O2.
  Catalase is a scavenger enzyme = catalytically prefect.
  Increase during exercise; more ROS = more SDM.

Question 6

Complex V: ATP Synthase

Answer 6

• ATP created by H+ gradient; but not by substrate-level phosphorylation.
• Chemiosmotic Theory: H+ gradient creates a proton-motive force.
  Work is needed, not spontaneous.
  Proton gradient is generated with energy from ETC by H+ pumping via Complex 1,3,4 from the matrix to intermembrane space of mitochondrion.
• P-side (IMS)
• N-side (matrix)
• C-ring: repeat alpha helices (mostly 10)
• Gamma: connects F0-domain-F1domain
• Alpha-3-Beta-3: alternates.
  Beta subunit = where ATP synthesis occurs, (ATPase activity) = where the active side.
  No ATPase activity in alpha.

Question 7

Boyer/Walker/Skow - 1997

Answer 7

• Skow: discovered Na2+/K+ Pump
• Mg2+ + ADP + Pi = [pentacovalent intermediate] = ATP + H20
  Pentacovalent intermediate is the last phosphate group that is covalently bonded to 5 O’s; one of the O’s will leave as H20 using H+ in the matrix to form it.
• Happens in B-subunit (F1-domain):
  Subtrate binds: ADP binding = L (loose).
  Product made: ATP made = T (tight-noR/T).
  Product released: ATP released = O (open).
• 3 B’s (a,b,c)
  a|L (120-degree rotation of gamma stalk in CCW) = T (made product) = O (released)
  b|O = L = T
  c|T = O = L
• Any single rotation, an ADP will be bind, made, and released.
• Alpha-subunits have ATP, but cannot push them out - thus, Beta-subunits can produce ATP.