Chapter 20 - The Electron Transport Chain

Question 1

Distinguish between an oxidizing agent and a reducing agent

Answer 1

An oxidizing agent, or oxidant, accepts electrons in redox reactions.

A reducing reagent, or reductant, donates electrons in such reactions.

Question 2

Explain why coenzyme Q is an effective mobile electron carrier in the electron transport chain.

Answer 2

The 10 isoprene units render coenzyme Q soluble in the hydrophobic environment of the inner mitochondrial membrane.

The two oxygen atoms can reversibly bind two electrons and two protons as the molecule transitions between the quinone form and the quinol form.

Question 3

What are the reactive oxygen species, and why are they especially dangerous to cells?

Answer 3

Hydroxyl radical (OH^-)
Hydrogen peroxide (H₂O₂)
Superoxide ion O₂^-
Peroxide O₂^2-

These small molecules react with a host of macromolecules - including proteins, nucleotides, and membranes - to disrupt cell structure and function.

Question 4

What is the advantage of having Complexes I, III, and IV associated with one another in the form of a respirasome?

Answer 4

The respirasome is another example of the use of supramolecular complexes in biochemistry. Having three complexes that are proto pumps associated with one another will enhance the efficiency of electron flow from complex to complex, which in turn will cause more efficient proton pumping.

Question 5

What are antioxidant vitamins?

Answer 5

Vitamin C and E

Question 6

What citric acid cycle enzyme is also a component of the electron transport chain?

Answer 6

Succinate dehydrogenase is a component of complex II

Question 7

Incompare fermentation and respiration with respect to electron donors and electron acceptors.

Answer 7

In fermentation, organic compounds are both the donors and acceptors of electrons.

In respiration, the electron donor is usually an organic compound, whereas the electron acceptor is an inorganic molecule such as oxygen.