Biology, Eighth Edition (Raven)

Chapter 7: How Cells Harvest Energy

Electron Transport System and Formation of ATP

How does Cyanide kill you? The final stage of cellular respiration is the electron transport chain (ETC). The ETC is a series of molecules embedded in the mitochondrial membrane. The first molecule accepts protons and electrons from the products of the Krebs Cycle. The electrons are passed from molecule to molecule and finally react with oxygen and protons to form water. Without oxygen the final reaction cannot occur. This causes a ‘traffic jam’ in that electrons further back on the chain cannot be transferred. The entire process stops. In the absence of oxygen the ETC stops working and no ATP is generated. Cyanide prevents oxygen from binding to the final molecule in the electron transport chain. Individuals poisoned with cyanide die from oxygen deprivation even though their cells may have abundant oxygen.

View the animation below, then complete the quiz to test your knowledge of the concept.


1.	The electron transport chain in bacteria is located...

		A)	in the cytoplasm.
		B)	in the mitochondria.
		C)	in the cell wall.
		D)	in the cell membrane.
		E)	in the plasmid.

2.	During aerobic respiration, the last carrier protein transfers a pair of electrons to...

		A)	water.
		B)	NADH.
		C)	oxygen.
		D)	Coenzyme Q.
		E)	a proton (H⁺).

3.	The function of the enzyme ATP synthase is to...

		A)	accept a proton from inside the cell membrane as it accepts electrons.
		B)	utilize the energy of the proton motive force to convert ADP to ATP.
		C)	produce reduced coenzymes like NADH.
		D)	transfer hydrogen to the electron transport chain.
		E)	shuttle electrons from NADH to a terminal electron acceptor.

4.	Electrons enter the electron transport chain when NADH transfers them there along with protons in the form of hydrogen.

		A)	True
		B)	False

5.	The electron transport chain consists of a series of membrane-bound carriers that shuttle protons and electrons to NADH.

		A)	True
		B)	False