Biochemistry : Electron Transport Chain Proteins and Complexes

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #11 : Electron Transport And Oxidative Phosphorylation

Where does oxidative phosphorylation take place in a eukaryote?

Possible Answers:

Nucleus

Lysosome

Endoplasmic reticulum

Cytoplasm

Mitochondria

Correct answer:

Mitochondria

Explanation:

Oxidative phosphorylation takes place in the mitochondria in a eukaryote.  The process is made possible by the double membrane within the mitochondria.

Example Question #71 : Carbohydrate Metabolism

How many protons in total are pumped into the intermembrane space of a mitochondria through the electron transport chain, if each complex individually receives 2 electrons?

Possible Answers:

8 protons

6 protons

12 protons

14 protons

10 protons

Correct answer:

12 protons

Explanation:

Complex I pumps 4 protons, complex IV pumps 4 protons, and the interaction between complex III and complex II is more complicated.

Complex II pumps no electrons in itself, but releases the fully reduced quinone species, , which interacts with complex III through the Q cycle. Simplified, the net result of the Q cycle is that 4 protons are pumped out into the intermembrane space. complex III pumps 2 protons from the mitochondrial matrix and 2 protons from .

This is a simplification of the 4 complexes, providing only the information necessary to complete the question. But a full understanding of the 4 complexes, and the flow of electrons is nonetheless essential for understanding why each complex pumps the number of protons it does.

Example Question #11 : Electron Transport Chain Proteins And Complexes

Which of the electron transport chain protein complexes accepts electrons from ?

Possible Answers:

All of the protein complexes accept electrons from 

Complex 2 (succinate dehydrogenase)

Complex 4 (cytochrome C oxidase complex)

Complex 1 (NADH-Q reductase complex)

Complex 3 (Cytochrome C reductase complex)

Correct answer:

Complex 2 (succinate dehydrogenase)

Explanation:

 first delivers its electrons to complex 2 of the electron transport chain. Subsequently, the electrons are delivered to ubiquinone, and then they move through complex 3, cytochrome C, and complex 4. Complex 2, therefore, is the only protein complex that directly accepts electrons from .

Example Question #11 : Electron Transport And Oxidative Phosphorylation

Which of the following is a unique property of complex 4 in the electron transport chain with respect to the other protein complexes?

Possible Answers:

It is the smallest of the protein complexes

It accepts electrons from 

It reduces oxygen to water

It is the only complex that does not pump hydrogens

It is the only complex that contains iron

Correct answer:

It reduces oxygen to water

Explanation:

The fourth complex in the electron transport chain is unique in that it has the important responsibility of reducing molecular oxygen to water. Oxygen is the final electron acceptor for cellular respiration, so this is a very important role. Complex 2 is the only one that accepts electrons from  and is the smallest of the protein complexes. Complex 2 is also the one that does not have hydrogen pumping ability. Iron is a component of complexes 1, 3, and 4.

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