Ch. 11 Flashcards
What is chemiosmosis?
- 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 does oxidative phosphorylation do for the cell?
- Generates ATP from the oxidation of metabolic fuels
- Accounts for 28 of 32 ATP obtained from glucose breakdown
What is the electron transport chain?
- 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 are the complexes in oxidative phosphorylation and what do they do?
What is the net reaction of oxidative phosphorylation?
2 NADH + 2 H+ + 5 ADP + 5 Pi + O2 –> 2 NAD+ + 5 ATP + 2 H2O
What are the key enzymes of oxidative phosphorylation?
- NADH–ubiquinone oxidoreductase (Complex I: oxidation of NADH and the reduction of FMN –> translocation of 4 H⁺ across the inner mitochondrial membrane)
- Ubiquinone–cytochrome c oxidoreductase (Complex III: oxidation of ubiquinol)
- Cytochrome c oxidase (Complex IV: accepts electrons from cytochrome c and donates them to O2 to form water
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)
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
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?
- Complex III
- Translocates 4 H+
- Passes 1 electron per Cyt C (there are 2 Cyt C so 2 electrons total)
What does Complex IV 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
- Forms H2O
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
1 NADH = ? ATP
2.5 ATP
What is the balanced equation of the ETS?
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 type of conditions favor ATP hydrolysis?
High ATP/ADP ratio
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 the 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 of the 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
