Quiz 13: Membranes and Transport (Ch 11, 12)

Which of the following statements describes the resting membrane potential of a neuron?

A state in which the flow of positive and negative ions across the plasma membrane is precisely balanced

Why do cells lack membrane transport proteins that are specific for the movement of O2?

Because oxygen dissolves readily in lipid bilayers

The diffusion of an integral membrane protein is studied by fluorescence recovery after photobleaching (FRAP). In this procedure, the protein of interest is labeled with a fluorescent marker, and the fluorescence in a small patch of membrane is then irreversibly "bleached" by a pulse of light from a focused laser. Which curve would most likely represent the behavior of the receptor once it has been activated by its signal molecule?

C

How do transporters and channels select which solutes they help move across the membrane?

Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.

Which of the following will produce the most fluid lipid bilayer?

Phospholipids with tails of 18 carbon atoms and two double bonds

The epithelial cells that line the gut have glucose-Na+ symport proteins that actively take up glucose from the lumen of the gut after a meal, creating a high glucose concentration in the cytosol. How do these cells release that glucose for use by other tissues in the body?

The cells have glucose uniports in their plasma membrane.

When the transport vesicle shown here fuses with the plasma membrane, which monolayer will face the cell cytosol?

The orange monolayer

In bacteria, the transport of many nutrients, including sugars and amino acids, is driven by the electrochemical H+ gradient across the plasma membrane. In E. coli, for example, a H+-lactose symporter mediates the active transport of the sugar lactose into the cell. Given what you know about coupled transport, which is likely true of the H+-lactose symporter?

The transporter oscillates randomly between states in which it is open to either the extracellular space or the cytosol.

Multipass transmembrane proteins can form pores across the lipid bilayer. The structure of one such channel is shown in the diagram. In this figure, the areas shown in red

the hydrophilic side chains of the transmembrane α helices.

In a lipid bilayer, lipids rapidly diffuse

within the plane of their own monolayer.