Chapter 11: Oxidative Phosphorylation Flashcards
What is Chemiosmosis?
- Proposed by Peter Mitchell
- Proton gradient is established across the mitochondrial inner membrane
- H+ travels from high to low
- Energy from H+ gradient is used to generate ATP
What is the Electron Transport Chain? What does it start and end with?
- Series of redox reactions that occur in a set of protein complexes embedded in the inner mitochondrial membranes
Start:
- NADH is oxidized into NAD+
- Citrate cycle is source of NADH
End:
- O2 reduced to H2O
What is the symbol for the chemical gradient? What is the symbol for membrane potential?
- ΔpH
- Δψ
How do protons behave like an electrical circuit?
- Resistor- ATP Synthase
- Capacitator - Proton Gradient
- Battery- Electron Transport System
Can the Proton circuit be uncoupled? what happens?
- Can be uncoupled to stop generating ATP
- Causes proton leakage resulting in heat
What do Thermogenin and Oligomycin do?
- Thermogenin passes H+ and energy released as heat
- Oligomycin blocks the flow of H+ through ATP synthase
Describe the structure of the mitochondria.
- Outer mitochondrial membrane
- Intermembrane space
- Inner mitochondrial membrane
- Cristae
- Mitochondrial matrix
What are the complexes and what do they do?
What is the net outcome of ET system?
Where does NADH Oxidation occur
Complex I
- Takes place on matrix side of inner mitochondrial matrix
- Two electrons initiate multiple Redox reactions
- O2 ends up being reduced to water
- Two electrons enter ET system through FADH2 oxidation
- Electron flow facilitated by sequential arrangement of electron carriers
How do electrons influence translocation of protons in the transport system?
- 2e- from NADH = 10 H+ translocated
- 2e- from FADH2 = 6H+ translocated
- Two new electron carriers
- Q-QH2
- Cytochrome C (ox-red)
Describe what happens in Complex I
- Protein: NADH-Ubiquinone oxido-reductase
- NADH is oxidized while Coenzyme Q is reduced
- Largest complex
- Covalently bound to Flavin (FMN)
- FMN accepts 2e- from NADH
Outline FMN reactions
Flavin mononucleotide (FMN) –red–> semiquinone –red–> Flavin mononucleotide (FMNH2)
What is the function of Fe-S clusters?
Complex I
- Exchange 1 e-
Fe3+ ⇋ Fe2+
What is coenzyme Q and what does it do?
- Coenzyme Q acts as a mobile electron carrier and transports electrons from Complex I to Complex III
- Ubiquinone (Q) is reduced to ubiquinol (QH2)
- 4 H+ are translocated from the matrix side of the membrane to the intermembrane space
How do electrons bind to form QH2
- NADH transfers 2e- to FMN
- 2e- Transferred from carrier to carrier
- 2e- +2H+ bind to Q making QH2
What does Complex II do?
- Protein: succinate dehydrogenase
- citrate cycle: catalyze oxidation reduction of succinate to fumarate
- Coupled redox reaction using FAD
- Reduces coenzyme Q to QH2
FADH2 + Q –> FAD+ + QH2
(no hydrogen translocation)
What does Complex III do?
- Protein: Ubiquinone-cytochrome C oxidoreductase
- Reduces cytochrome c and translocates 4 H+
- Docking site for QH2 and Cytochrome c
- Contains binding sites for ubiquinone (Qp and Qn)
- Transfers e- through an iron sulfur cluster center
- Contains 11 different protein subunits
What is the Q cycle?
- Converts 2e- transport process into 1e- transfers
- Electrons come from QH2
- Occurs in Complex III
- Cytochrome c is reduced in the process
- Cytochrome c transports 1 e- from Complex III to Complex IV
What is Complex IV and what does it do?
- Protein: Cytochrome c Oxidase
- Accepts electrons one at a time
-cytochrome C is oxidized while O2 is reduced
-2 copper center - Cu2+ <–> Cu+
- 2H+ are translocated across the membrane
2 cytochrome c (red) + 4 HN+ + ½ O2 → 2 cytochrome c (ox) + 2HP+ + H2O
How many protons are required to synthesize 7 ATP?
10 protons
How many ATP does the oxidation of 1 NADH result in?
2.5 ATP
What is the balanced equation of the ET system?
2 NADH + 2 H+ + 5 ADP + 5 Pi + O2 → 2 NAD+ + 5 ATP + 2 H2O
How many large structural components are there in ATP Synthase complex and what do they do?
F1- encodes catalytic activity
Fo - acts as protein channel crossing the inner mitochondrial membrane
What subunits does the rotor of ATP synthase complex consist of?
– γ,δ,ε subunits
What subunits does the headpiece of ATP synthase cpmplex consist of?
Catalytic part: α3β3 unit
What does the Stator do in ATP synthase complex?
It is the immobile stabilizing arm
What three states can the F1 subunit be in? How much does the Rotor rotate and when is ATP released?
- L(loose), T(tight), and O(open)
- 120 degree rotation (clockwise)
- ATP only released in open position
Which subunit contains ATP/ADP binding sites?
Beta
How does ATP binding affinity change in the different states?
What are the outcomes of ADP binding?
- 10 protons used in one round
- Generate 3 ATP
How does F0 rotate?
Asp 59 is protonated
- COO- –> COOH
Outline the Six steps of F0 rotation.
What type of conditions favor ATP hydrolysis?
High ATP/ADP ratio
What are two translocases in Oxphos?
- ATP/ADP
- Pi
What are two shuttles for translocation of 2e- from cystolic NADH?
- Malate-aspartate shuttle (liver)
- Glycerol-3-phosphate (muscle)
How is ADP + Pi imported into mitochondrial matrix?
- Translocase proteins located in inner mitochondrial matrix
What does ATP/ADP translocase do?
- Exports 1 ATP for every ADP imported
- Antiport
- Switch between cytosolic and matrix states
What does phosphate translocase do?
- Translocates 1 Pi and H+ into the matrix
- Can be symporter or antiporter
- Resembles a channel
What is the Malate-Aspartate Shuttle?
- Primary shuttle in liver, kidney, and Heart
- All reactions are reversible
- NADH will not be imported into the matrix
- Electrons find another way into matrix
- Supply of NAD+ is maintained
Outline the four steps in Malate Aspartate shuttle.
- Oxaloacetate + NADH + H+ is reduced by cytosolic malate dehydrogenase to form Malate and NAD+
- Malate is transported into mitochondrial matrix and oxidized by mitochondrial malate dehydrogenase with NAD+ to form oxaloacetate and NADH + H+
- Transamination of Oxaloacetate by mitochondrial aspartate aminotransferase and glutamate to formAlpha ketoglutarate and aspartate which is shuttled across the membrane
- Transamination of aspartate in the cytosol by cytosolic aspartate aminotransferase and Alpha ketoglutarate to form oxaloacetate and glutamate
What is glycerol-3-phosphate shuttle?
- In skeletal muscle and brain
- Delivers electrons from NADH to the mitochondrial matrix using FAD
- Electrons from NADH2 go via FADH2 into electron transport system through coenzyme Q
- Consists of two isozymes of glycerol-3-phosphate dehydrogenase
Outline the three steps involved in Glycerol-3-phosphate shuttle.
- Glycolytic intermediate (dihydroxyacetone phosphate) in cytosol is reduced forming glyerol-3-phosphate which diffuses across outer mitochondrial membrane through porin channels
- Glycerol-3-phosphate is reoxidized in intermembrane space forming dihydroxyacetone phosphate, 2e- are transfered to FAD in mitochondrial glycerol-3-phosphate dehydrogenase (regenerates dihydroxyacetone phosphate is recycled via porin channels)
- 2e- passed to Q which transfers them one at a time to complex III via Q cycle
How much ATP is generated by one glucose in liver cells via malate-aspartate shuttle? How about glycerol-3-phosphate shuttle in muscle cells?
32 in liver cells
30 in muscle cells
What do ADP/ATP and NADH/NAD+ ratios regulate?
ADP/ATP: Control aerobic respiration
NADH/NAD+: in mitochondrial matrix control steps in the citrate cycle
What happens to O2 consumption and ATP synthesis when inhibitors of ETS are added?
O2 consumption and ATP production shut down
Where does cyanide bind in ETS and what happens
- Binds to complex IV and causes no electron transfer to O2 which stops ATP synthesis
What does oligomycin do?
blocks H+ flow in ATP synthesis
What does 2,4 dinitrophenol do?
Transports H+ across the membrane uncoupling the ETS and ATP synthesis
What is the difference between brown and white adipose tissue?
Brown:
- Smaller droplets leave more space for mitochondria
White:
- Large fat droplet fills cytosolic space in each cell
Where does Rotenone bind?
Inhibits Complex I
Where does hydrogen cyanide bind?
Inhibits Complex IV
Where does Carbon Monoxide bind?
Inhibits Complex IV
Where does antimycin A bind?
Inhibits Complex III
Where does Venturicidin bind?
Inhibits ATP synthase
Where does DCC bind?
Inhibits ATP synthase
Where does Bongkrekic acid bind
Inhibits ATP/ADP translocase
What do inherited mitochondrial disease cause?
Decreased ATP production
What is LHON
- Complex I
- Only passed on by females
- Severity dependent on ratio of normal/mutant mitochondria
- During aging disease may worsen
