Electron Transport Chain And Oxidative Phosphorylation Flashcards
Briefly describe oxidative phosphorylation
- Oxidize NADH and FADH2
- Generate electrical energy by passing electrons to Oxygen
- create a proton gradient across inner mitochondrial membrane
- proton gradient drives phosphorylation of ADP to ATP
Where is the electron transport chain?
Inner mitochondrial membrane
The ETC uses NADH and FADH2, where are these generated?
In the make ATP and ADP using energy stored in NADH and FADH2
Generated through catabolic processes such as glycolysis , Pyruvate dehydrogenase (PDH ) and TCA
What structures and enzymes are located within the mitochondria?
-ATP synthesizing structures (ATP synthase) and San electron transport assembly in the inner mitochondrial membrane.
The following in the mitochondrial matrix:
- TCA cycle enzymes
- Fatty acid oxidation enzymes
- mtDNA, mtRNA
- Mitochondrial ribosomes
Describe briefly the mitochondrial inner membrane
Impermeable to most small ions, small and 9arge molecules
What are the 2 stages we can break this process down to?
- Electron transport
2. Oxidative phosphorylation and the Chemiosmotic hypothesis
What is the role of NADH and FADH2 in electron transport?
- NADH and FADH2 donate electrons to complexes in the inner mitochondrial membrane
- the electrons flow Through the complexes and are eventually donated to oxygen forming water
What happens to protons in the Electron transport chain?
- Process pumps protons (H+) into the inter-membrane space
- this establishes a H+ gradient across the inner mitochondrial membrane
- There is a high concentration of protons in the in the inter-membrane space and low concentration in the matrix
Explain the chemiosmotic hypothesis and oxidative phosphorylation
- this proton gradient causes protons to flow through ATP synthase in the inner membrane resulting in production of ATP
- the H+ gradient couples electron transport to ATP synthesis
What are the 4 protein complexes of the Electron transport chain?
Complex 1 - NADH dehydrogenase
Complex 2- Succinate dehydrogenase
Complex 3- cytochrome reductase
Complex 4 - cytochrome oxidase
What are the functions of 4 protein complexes in ETC?
These four complexes accept or donate electrons to relatively mobile electron carriers such as :
Coenzyme Q
Cytochrome C
How do protein ETC complexes interact with prosthetic groups?
Prosthetic groups in each complex reversibly accept and release electrons
What are the prosthetic groups for ETC Complexes I and II?
-FMN and FAD (riboflavin derivative), respectively
What is the prosthetic group of Compex III in the ETC?
Heme group (Fe2+)
What are the prosthetic groups of protein complex IV in the ETC?
Cu2+ and heme group(Fe2+)
Complexes I, II and III also contain….
Iron-sulfur proteins
Where do Complex 1 electrons come from?
-NADH electrons come from malate dehydrogenase(MDH, a-keto glutamate dehydrogenase(a-KGDH), isocitrate dehydrogenase(IDH), Pyruvate dehydrogenase (PDH) as well as fatty acid B-oxidation and from cytosolic sources such as glycolysis
Where do the electrons for Complex 2 come from?
-FADH2 electrons from Succinate dehydrogenase (SDH) or the associated Coenzyme Q(CoQ) gets them from glycerol phosphate shuttle or from fatty acid B-oxidation
Outline the flow of electrons during electron transport
- NADH oxidized by CoQ at complex I and/or FADH2 oxidized by CoQ at complex II
- CoQ oxidized by Cytochrome c and Complex II
- Cytochrome c oxidized by oxygen at complex IV
- O2 is the final electron acceptor at complex IV
Explain the ending of Oxidative Phosphorylation and chemiosmotic hypothesis
- As electrons flow down electrochemical potential, protons are pumped into the inter membrane space
- Protons are pumped into the intra membrane space at complexes I, III and IV
- This creates a pH gradient that is relieved by pumping protons back through F0F1-ATP synthase(COMPLEX V).
The energy released in this process is coupled to ATP synthesis from ADP and Pi
Explain the inhibition of electron transport
- Rotenone, piericidin A(bacterial antibiotic) and the barbiturate Amytal inhibit NADH dehydrogenase in complex 1
- Antimycin (an antibiotic) inhibits cytochrome b of cytochrome reductase(complex III)
- CO, azide, hydrogen sulphide(H2S) and cyanide (CN-) inhibit cytochrome oxidase(complex IV)
- Oligomycin(a streptomyces antibiotic) inhibits ATP synthase
What are the effects of ETC inhibitors?
Inhibitors decrease ATP synthesis, decrease ETC and Oxygen consumption
How are ATP and ADP transported?
- Adenine nucleotide translocase: unidirectional exchange of ATP for ADP(antiport)
- Symporters of Pi and H+ is electro-neutral
What chemicals inhibit ADP/ATP transport?
Atractyloside
Bongkrekic acid
Effects of both of these are similar to oligomycin
How does Atractyloside inhibit ADP/ATP transport?
Atractyloside: a toxic glycoside(molecule with a sugar and a non carbohydrate element) from thistle plant Atractylis gummifera)
-Binds the outward facing (inter-membrane space) portion of the adenine nucleotide transporter
How does Bongkrekic acid inhibit ADP/ATP transport?
Respiratory toxin produced in coconuts contaminated with Burkholderia gladioll
-Binds the inward facing (matrix) portion of the adenine nucleotide transporter
What is the purpose of uncoupled of oxidative phosphorylation?
Uncouplers decrease ATP synthesis, increase ETC and OXYGEN consumption
How do certain uncouplers act?
Certain uncouplers (e.g. DNP(dinitrophenol) ASA(aspirin), thermogin, ionophores) act by destroying the proton gradient
What is the mechanism of uncouplers of oxidative phosphorylation?
Uncoupling proteins create a “proton leak”, allowing protons to renter the mitochondrial matrix without capturing any energy as ATP
Why are shuttle mechanisms needed?
- inner mitochondrial membrane is impermeable to most proteins and coenzymes
- Need shuttle to deliver electrons from NADH (from glycolysis in the cytosol) across the inner mitochondrial membrane
What are the 2 shuttle mechanisms?
- Glycerol phosphate shuttle
- malate-Aspartate shuttle
What is the P/O ratio?
The P/O ratio= ratio of ATP formed per Onatom reduced divided by Phosphorylated nucleotide/oxygen needed
Varies between NADH and FADH2
What is the P/O ratio of NADH?
P/O ratio for NADH is 3 ATP: 1 NADH oxidized by the ETC
What is the P/O ratio for FADH2?
P/O ratio FADH2 is 2 ATP :1 FADH2 oxidized by the ETC
Describe the energy yield of the ETC
The oxidation of 1 NADH yields enough energy for:
- 3 moles of ATP(malate-Aspartate shuttle)
- 2 moles of ATP (glycerol phosphate shuttle)
The oxidation of 1 FADH2 yields enough energy for about 2 moles of ATP
What are the principle controls of ATP production ?
[NADH][NAD+]
And
[ATP][ADP]
I.e. ETC will be active when
[ADP][ATP] and [NADH][NAD+]
What is hypoxia? What are the effects?
- Hypoxia decreases the rate of ETC and ATP production
- A drop in cellular ATP increases anaerobic glycolysis and lactic acidosis production, anaerobic glycolysis cannot meet most tissue demands (neural tissue, cardiac muscle)
- Myocardial infarction (heart attack) can result from hypoxia
