Introduction to membrane transport

The fluid mosaic model of membrane structure suggests that membranes

• are composed of a fluid bilayer of fatty acids with proteins associated on the outer and inner surfaces.

• are composed of protein molecules embedded in a fluid bilayer of phospholipids.

• are composed of a single fluid layer of phospholipids and proteins.

• are composed of a fluid phospholipid bilayer sandwiched between two layers of hydrophilic proteins.

Which of the following molecules are localized on the exterior of a phospholipid bilayer?

• saturated fatty acids

• unsaturated fatty acids

• phosphate groups

• cholesterol

At human body temperature (37°C), cholesterol in membranes functions to

• make the membrane less fluid by restricting the movement of phospholipids.

• make the membrane more fluid by stimulating the movement of phospholipids.

• facilitate cell-cell interactions by binding to receptors on neighboring cells.

• make the membrane more fluid by crowding integral membrane proteins into restricted areas.

Which of the following membrane proteins tend to lack hydrophobic regions on their surfaces?

• transmembrane proteins

• integral membrane proteins

• peripheral membrane proteins

• integrins

How do unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

• The double bonds form kinks in the fatty acid tails that prevent adjacent lipids from packing tightly together.

• Unsaturated fatty acids have a higher cholesterol content that prevents adjacent lipids from packing tightly together.

• Unsaturated fatty acids are more polar than saturated fatty acids.

• The double bonds result in shorter fatty acid tails and therefore thinner membranes.

A protein that spans the phospholipid bilayer one or more times is

• a transmembrane protein

• a glycoprotein

• a peripheral protein

• an extracellular matrix protein

What kinds of molecules pass through a cell membrane most easily?

• large hydrophobic

• small hydrophobic

• large polar

• small ionic

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

• It is a peripheral membrane protein

• It exhibits a specificity for a particular type of molecule

• It requires the expenditure of cellular energy to function

• It works against a concentration gradient

Which of the following statements about diffusion is correct?

• It requires an expenditure of energy by the cell

• It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration

• It is an active process in which molecules move from a region of lower concentration to one of higher concentration

• It is a passive process in which molecules move from a region of lower concentration to a region of higher concentration

Water can move quickly through the plasma membrane of some cells because

• it moves through hydrophobic channels

• water movement is tied to ATP hydrolysis

• it is a small, nonpolar molecule

• it moves through aquaporin channel proteins.