Electron Transport and ATP Synthesis
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Transcript of Electron Transport and ATP Synthesis
Electron Transport and ATP Synthesis
C483 Spring 2013
1. To reduce one molecule of O2, ________ electron(s) must be passed through the electron transport chain and ________ molecule(s) of NADH is(are) oxidized.A) 4; 2B) 2; 1C) 1; 1D) 1; 2E) 4; 4
2. The chemiosmotic theory is a concept that ________. A) the transport of Na+ and K+ across cell membranes is by active transport B) explains how transport by facilitated diffusion reaches a saturation limit C) explains the blood-brain barrier D) a proton gradient drives the formation of ATP
3. Which is the proper ranking of greatest to least reduction potential? A) NAD+, Q, O2B) O2, Q, NAD+C) Q, NAD+, O2D) Q, O2, NAD+
4. According to the binding change mechanism, the (alpha3 beta3 ) oligomer of ATP synthase has 3 catalytic sites which can each have ________ different conformations.A) 2B) 3C) 6D) 9
5. The P/O ratio for passing electrons through complexes I, III and IV is ________.A) 1B) 1.5C) 2D) 2.5E) 3
Goal: ATP Synthesis
Overview• Redox reactions• Electron transport chain• Proton gradient
• ATP synthesis• Shuttles
Analogy: How does burning coal put flour in the grocery store?
Redox reactions: electricity
• 2 e- transfer• Calculate DG by
reduction potential• NADH: Eo’ = -.32• FMN: Eo’=-.30• DGo’ = -nFDEo’ = -2(96485)(0.02)= -3.9 kJ/mol
N
R
H2N
O H H
NR
N
N
NHR
R
O
O
H+
NADH FMN
N
R
H2N
O
NR
HN
NH
NHR
R
O
O
NAD+ FMNH2
Coenzyme Q: Mobile Carrier
• FADH2 is a one e- donator
• Many reactions, including metals
• Ubiquinone is a key intermediate
• Can diffuse through nonpolar regions easily
Numerous Redox Substrates• O2: high “reduction potential”• Substrates– Organic cofactors– Metals (iron/sulfur clusters)– cytochromes
Oxygen: the final electron acceptor
• Water is produced—has very low reactivity, very stable
• Superoxide, peroxide as toxic intermediates
• Overall reactionNADH + H+ + ½ O2 NAD+ + H2O
Flow Through Complexes
Downhill Flow of Electrons
Compartmentalization
Protonmotive Force• Flow of electrons is
useless if not coupled to a useful process– Battery connected
to wire• Proton gradient
across mitochondrial membrane
Overview of Complexes I-IV• Don’t need to know which cofactors in which
complexes, mechanism of proton pumping• Complex I and II are different entry points into
Q pool, which goes to Complex III
Protonmotive Force
• NADH + H+ + ½ O2 NAD+ + H2O + 10 H+ pumped
• succinate + ½ O2 fumarate + H2O + 6 H+ pumped
Proton Gradient
• Gradient driven by concentration difference + charge difference
• Free energy of ATP hydrolysis = -48 kJ/mole• How many protons needed to fuel ATP
formation? Minimum of 3
Using the Gradient
• Coupled to ATP synthesis• Uncouplers used to show
link of oxygen uptake and ATP synthesis
Complex V: ATP Synthase
• Molecular motor• Rotor: c, g, e– Proton channel
Proton Channel• Protons enters channel
between rotor and stator (unit a--purple)
• Rotor rotates to release strain by allowing proton to enter matrix
• “Stalk” (g) moves inside the “knob”—hexameric ATP synthase
• 9 or 10 protons = full rotation
Binding-Change Mechanism• Stalk causes ATP synthase to have three different
conformations: open, loose, tight• In “tight” conformation, energy has been used to
cause an energy conformation that favors ATP formation
• 9 protons = 3 ATP (or 1 ATP/3 protons)
Remember Analogy
• Fuelelectricitywater pumped uphillflows down to grind flour
• But we don’t have bread until flour is transported to where it needs to go!
• Compartmentalization: ATP is in matrix, but must get to the rest of the cell
Active Transport of ATP
• ATP must go out, ADP and Pi must go in• Together, use about 1 proton of protonmotive
force
Energy Accounting• ATP costs 4 protons– 3 protons in ATP synthase, 1 proton in transport
• NADH pumps 10 protons – 4 protons in Complex I, 4 protons in Complex III, and 2
protons in Complex IV– 2.5 ATP/NADH • called P/O ratio--# of phosphorylation per oxygen atom
• QH2 pumps 6 protons– 4 protons in Complex III and 2 protons in Complex IV– 1.5 ATP/QH2
Net ATP Harvest from Glucose
• Glycolysis = 2 ATP– Plus 3 or 5 ATP from
NADH– What leads to
difference in this case?• Pyruvate DH = 5 ATP• Citric Acid Cycle = 20
ATP• Total: 30-32
ATP/glucose
NADH Shuttles
• Glycerol phosphate shuttle (1.5 ATP/NADH)
• Produces QH2
• Operational in some tissues/circumstances
NADH Shuttles
• Malate-Aspartate shuttle (2.5 ATP/NADH)– Actually slightly less
because one proton is consumed in shuttle
• Separate NAD+/NADH pools indirectly interconverted
• Operational in some tissues/circumstances
Answers
1. A2. D3. B4. B5. D