Bil 255 Exam 3 in class quiz questions

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 A voltage difference across the plasma membrane when the neuron has been stimulated A voltage difference across the plasma membrane, with more positive membrane potential inside A voltage difference of 0 millivolts (mV) across the membrane A voltage difference that is chiefly a reflection of the electrochemical Na+ gradient across the plasma membrane

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 concentration must be kept low inside cells to avoid creating reactive superoxide radicals that can damage DNA and proteins Because oxygen dissolves readily in lipid bilayers Because oxygen is transported in and out of the cell by special oxygen-binding proteins such as hemoglobin Because oxygen, dissolved in water, can enter cells via aquaporins Because transport of oxygen across cell membranes is energetically unfavorable

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. The time it takes for fluorescence to return to the bleached membrane patch provides a measure of how rapidly unbleached, fluorescently labeled proteins diffuse through the bilayer into the area. This "recovery" is plotted on a curve that shows fluorescence over time. For one protein, which acts as a receptor for an extracellular signal molecule, stimulation by its signal ligand causes the receptor to interact with other membrane proteins, forming a large protein signaling complex. Shown first is the FRAP result for the unstimulated receptor. Which curve would most likely represent the behavior of the receptor once it has been activated by its signal molecule?

C: slow rising check mark curve

How do transporters and channels select which solutes they help move across the membrane? Both channels and transporters discriminate between solutes mainly on the basis of size and electric charge. Channels allow the passage of solutes that are electrically charged; transporters facilitate the passage of molecules that are uncharged. 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. Channels will allow the passage of any solute as long as it has an electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate. Transporters discriminate between solutes mainly on the basis of size and electric charge; channels bind their solutes with great specificity in the same way an enzyme binds its substrate.

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? Large amounts of cholesterol Phospholipids with fully saturated tails of 18 carbon atoms Phospholipids with fully saturated tails of 20 carbon atoms Phospholipids with tails of 18 carbon atoms and two double bonds Phospholipids with tails of 20 carbon atoms and two double bonds

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. Glucose diffuses down its concentration gradient through the lipid bilayer of the plasma membrane. The cells have a glucose pump that expels the glucose needed by other tissues. The cells have glucose channels in their plasma membrane. The cells run the glucose-Na+ symport proteins in reverse.

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? Half the time the orange monolayer will face the cytosol, and half the time the blue monolayer will face the cytosol. It depends on the cargo the vesicle is carrying. It depends on whether the vesicle is coming from the endoplasmic reticulum or the Golgi apparatus. The blue monolayer The orange monolayer

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? If the H+ gradient were reversed, the transporter could serve as a H+-lactose antiport. Lactose and H+ ions bind to two different conformations of the transporter. The transporter goes through an intermediate state in which the lactose-binding site is open to both sides of the membrane. The transporter oscillates randomly between states in which it is open to either the extracellular space or the cytosol. To undergo the conformational change that releases lactose into the cell, the transporter hydrolyzes ATP.

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

In a lipid bilayer, lipids rapidly diffuse: back and forth from one monolayer to the other in the bilayer. both within the plane of one monolayer and back and forth between the monolayers. in and out of the bilayer. within the plane of their own monolayer. None of the above: lipids remain in place within the bilayer

Within the plane of their own monolayer

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 represent: small, water-soluble molecules. the amphipathic side chains of the transmembrane α helices. the hydrophilic side chains of the transmembrane α helices. the hydrophobic lipid tails of the bilayer. the hydrophobic side chains of the transmembrane α helices.

the hydrophilic side chains of the transmembrane α helices.