AP Bio chp 5

Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At high temperatures, these regions...

• are more fluid than the surrounding membrane

• are less fluid than the surrounding membrane

• are able to flip from inside to outside

• detach from the plasma membrane and clog arteries

Singer and Nicolson's fluid mosaic model of the membrane proposed that membranes

• are a phospholipid bilayer

• are a phospholipid bilayer between two layers of hydrophilic proteins

• are a single layer of phospholipids and proteins

• consist of protein molecules embedded in a fluid bilayer of phospholipids

Which of the following types of molecules are the major structural components of the cell membrane?

• phospholipids and cellulose

• nucleic acids and proteins

• phospholipids and proteins

• proteins and cellulose

When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that...

• the integral membrane proteins are not strong enough to hold the bilayer together

• water that is present in the middle of the bilayer freezes and is easily fractured

• hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing

• the hydrophobic interactions that hold the membrane together are weakest at this point

The presence of cholesterol in the plasma membranes of some animals...

• enables the membrane to stay fluid more easily when cell temperature drops

• enables the animal to remove hydrogen atoms from saturated phospholipids

• enables the animals to add hydrogen atoms to unsaturated phospholipids

• makes the animal more susceptible to circulatory disorders

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

• They can move laterally along the plane of the membrane

• They frequently flip-flop from one side of the membrane to the other

• They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane

• They are free to depart from the membrane and dissolve in the surrounding

  solution

Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold?

• by increasing the percentage of unsaturated phospholipids in the membrane

• by increasing the percentage of cholesterol molecules in the membrane

• by decreasing the number of hydrophobic proteins in the membrane

• by cotransport of glucose and hydrogen

In order for a protein to be an integral membrane protein it would have to be...

• hydrophilic

• hydrophobic

• amphipathic, with at least one hydrophobic region

• completely covered with phospholipids

When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are

• peripheral proteins

• phospholipids

• carbohydrates

• integral proteins

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

• The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly

• Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in their membranes

• Unsaturated fatty acids are more polar than saturated fatty acids

• The double bonds block interaction among the hydrophilic head groups of the lipids