Biology, Eighth Edition (Raven)

Chapter 38: Transport in Plants

Proton Pump

What is the use of a concentration gradient across a membrane? When a molecule or an ion is moved across a membrane from an area of low concentration to an area of high concentration then a gradient is generated. This gradient can be chemical or it can also create a difference in electrical charge across the membrane if ions are involved. The concentration is a source of potential energy. The gradient is analogous to picking up objects that are on the floor and placing them on a table. The objects can now be pushed off and the energy of their fall can be used to perform a task, just as falling water can be used to generate electricity. The proton pump generates an electrical and chemical gradient that can be used to create ATP which can drive a large number of different biochemical reactions.

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


1.	Proton pumps are protein complexes that

		A)	break down water into hydrogen and oxygen.
		B)	synthesize water from hydrogen and oxygen.
		C)	pump protons and electrons through the cell membrane.
		D)	pump protons from the exterior of the cell to the interior.
		E)	pump protons from the interior of the cell to the exterior.

2.	Synthesis of ATP via a proton gradient is called

		A)	glycolysis.
		B)	krebs cycle.
		C)	chemiosmosis.
		D)	substrate-level phosphorylation.
		E)	fermentation.

3.	Which of the following is the enzyme used to synthesize ATP?

		A)	ATP phosphodiesterase
		B)	ATP hydrolase
		C)	ATP kinase
		D)	ATP phosphorylase
		E)	none of the above

4.	The protons are generated during oxidation reactions.

		A)	True
		B)	False

5.	The membrane is permeable to protons.

		A)	True
		B)	False