S1B4 - Electron Transport Chain Flashcards
(40 cards)
Name the protein components of the mitochondrial electron transport chain. Include the name and complex number.
- Complex I - NADH dehydrogenase
- Complex II - Succinate dehydrogenase
- Complex III - ubiquinone: cytochrome c oxidoreductase
- Cytochrome c
- Complex IV - Cytochrome oxidase
- Complex V - ATP synthase
What is the main function of flavoproteins, heme containing cytochromes, copper in complex IV, and UQ?
Flavoproteins transfer electrons along the electron transfer chain
What do you need to know about coenzyme Q?
Coenzyme Q (aka ubiquinone)
- Ubiquinoneis a lipid-soluble conjugated dicarbonyl compound that readily accepts electrons
- Upon accepting two electrons, it picks up two protons to give an alcohol, ubiquinol
- Ubiquinol can freely diffuse in the membrane, carrying electrons with protons from one side of the membrane to another side
- Coenzyme Q is a mobile electron carrier transporting electrons from Complexes I and II to Complex III
Name the entry point in the electron transport chain for the electrons from the following biological fuels:
- fatty acid oxidation
- succinate oxidation (citric acid cycle)
- NADH
- succinate
- Glycerol 3-phosphate
- Acyl-CoA dehydrogenase
- Q
- Q
- through a flavoprotein with the cofactor FMN to a series of FE-S centers (in Complex I) and then to Q
- through a flavoprotein with the cofactor FMN to a series of FE-S centers (in Complex II) and then to Q
- to a flaviprotein on the outer face of the inner mitochondrial membrane, then to Q
- to electron-transferring flavoprotein (EFT), from which they pass to Q via ETF: ubiquinone oxidoreductase
What does Myxothiazol do?
Myxothiazol prevents electron flow from QH2 to the Rieske iron-sulfur protein, binds at Qp. This all takes place in complex III.
How many electrons from NADH to O2 result in the translocation of how many protons across the membrane. How many protons from Complex I & IV? How many from Complex II?
2e from NADH to O2 result in the translocation of 10 protons across the membrane, 4 each from Complex I & IV and 2 from Complex II.
Describe the two main functional subunits of ATP synthase.
- F1
- soluble complex in the matrix
- individually catalyzes the hydrolysis of ATP
- F0
- integral membrane complex
- Transports protons from IMS to matrix, dissipating the proton gradient
- Energy transferred to F1 to catalyze phosphorylation of ADP
Describe Leber hereditary optic neuropathy (LHON).
- LHON affects CNS causing sudden–onset blindness in early childhood due to death of the optic nerve
- LHON results from single base change in the mitgenes encoding three subunits of complex I (ND1, 4, & 6) lowering its activity
- Patients with lowered amount of muted mitDNAdevelop symptoms and blindness in early adulthood while patients with higher percent of mutated mitDNAdevelop sever disease in early childhood
What are the two different shuttles used to transport NADH across the inner mitochondrial membrane? Which is more energy efficient?
Since NADH cannot cross the mitochondrial membrane, cytosolic electrons carried by NADH are carried across the mitochondrial membrane via two shuttle pathways:
- The primary NADH electron transport system is the malate-aspartate shuttle, which transports NADH electrons to complex I in the mitochondria.
- The less commonly used NADH electron transport system is the glycerol-3-phosphate (G3P) shuttle. In the G3P shuttle, NADH reduces dihydroxyacetone-phosphate to G3P, which can cross the inner mitochondrial membrane. G3P is then oxidized back to dihydroxyacetone-phosphate by FAD+ to form FADH2. FADH2 donates its electrons to complex II. Because NADH is converted to FADH2 in this system, it is less efficient than the malate-aspartate shuttle.

For each of the following electron transport chain toxins, would there be an increased or decreased proton gradient and oxygen consumption compared to normal: Rotenone? Oligomycin? 2,4-Dinitrophenol?
What toxin inhibits ATP synthase directly by blocking its proton channel?
Oligomycin (a macrolide) inhibits ATP synthase (complex V) by blocking its proton channel (specifically the Fo subunit, “o” for oligomycin).
Reduced nicotinamide adenine dinucleotide produced during glycolysis is shuttled into mitochondria to provide electrons for oxidative phosphorylation. Which of the following molecules is NOT involved in the most common shuttle mechanism?
A) Aspartate
B) Alanine
C) Oxaloacetate
D) Malate
E) Glutamate
The malate-aspartate shuttle is used to shuttle NADH into mitochondria. The process starts with oxaloacetate + NADH becoming malate. Malate is able to enter the mitochondria, where it is converted back to OAA + NADH. OAA is unable to leave the mitochondria, but it can be converted to aspartate using glutamate as an amino group donor. The aspartate enters the cytosol and is converted back to OAA. Alanine is NOT involved in the malate-aspartate shuttle.
Which two toxins can bind and disrupt NADH dehydrogenase (or complex I) of the ETC? Which toxin can do this to cytochrome c reductase (complex III)?
Amobarbital (known as amytal) and rotenONE bind to NADH dehydrogenase (complex I) and directly inhibit electron transport.
Antimycin A (“AnTHREEmycin”) binds to cytochrome c reductase (complex III) and directly inhibits electron transport.
How does 2,4-dinitrophenol inhibit aerobic respiration?
2,4-Dinitrophenol and increased doses of aspirin increase the permeability of the inner mitochondrial membrane leading to a decreased proton gradient and increased oxygen consumption. Heat is generated instead of ATP (this explains the fever generated following toxic doses of aspirin.)
What two tissues are most severely affected when exposed to toxins that disrupt any component of the electron transport chain?
Toxins that disrupt any component of the ETC disrupt the aerobic production of ATP. Tissues that depend highly on aerobic respiration, such as the CNS and the heart, are particularly affected.
To what enzyme do carbon monoxide and cyanide bind in the electron transport chain?
Carbon monoxide and Cyanide bind to Cytochrome C oxidase (complex IV) and directly inhibit electron transport.
In neonates, brown fat is metabolized for heat production. To accomplish this, the proton gradient across the mitochondrial membrane is disrupted. Which of the following toxins similarly disrupts the proton gradient?
A) Oligomycin
B) Glutamate
C) Cyanide
D) Carbon monoxide
E) 2,4-dinitrophenol
E) 2,4-dinitrophenol
- 2,4-dinitrophenol transports protons across the mitochondrial membrane, inhibiting the electron transport system.
- Oligomycin inhibits ATP synthase.
- CO and CN bind to cytochrome c oxidase, consuming oxygen and depriving the mitochondria of an electron receptor.
What is the final electron acceptor of the electron transport chain?
Molecular oxygen, O2, is the final electron acceptor.

What powers ATP synthase to generate ATP?
ATP Synthase (Complex V): uses the electrochemical proton gradient created by the ETC to produce ATP from ADP and Pi.

What is the main function of the electron transport chain? In humans, where is the electron transport chain located?
Electron transport chain (oxidative phosphorylation): uses NADH and FADH2 electrons (from glycolysis, pyruvate dehydrogenase complex, and the citric acid cycle) to form a proton gradient. The proton gradient drives the production of ATP.
The ETC (electron transport chain) is composed of 5 multi-enzyme complexes, numbered I-V. It is embedded in the inner mitochondrial membrane.
Carbon monoxide, in addition to binding heme, can also directly disrupt a process that is central to ATP synthesis. To which enzyme does carbon monoxide bind?
A) Succinate dehydrogenase
B) Pyruvate kinase
C) Cytochrome c oxidase
D) Isocitrate dehydrogenase
E) Adenosine triphosphate synthase
C) Cytochrome c oxidase
CO binds to cytochrome c oxidase in the electron transport chain.
In the electron transport chain, what is the ATP yield per molecule of NADH? FADH2?
1 NADH yields 2.5 ATP and 1 FADH2 yields 1.5 ATP. The reason for the lower energy yield of FADH2 is that NADH electrons are transferred to complex I while FADH2 electrons are transferred to complex II.
- Complex II is succinate dehydrogenase of the citric acid cycle.
What are the mobile electron carriers of the electron transport chain?
Mobile electron carriers coenzyme Q and cytochrome c shuttle electrons between enzyme complexes of the ETC.
- coenzyme Q shuttles electrons from complexes I and II to complex III.
- cytochrome c shuttles electrons from complex III to complex IV.
What provides the energy for creating the proton gradient in the electron transport chain?
The flow of electrons (provided by NADH and FADH2) through the ETC provides the energy to pump protons into the mitochondrial inter-membrane space. This creates an electrochemical proton gradient.
