3.4.2 The Plasma Membrane: The Fluid-Mosaic Model

Question 1

plasma membrane

Answer 1

• described as a fluid mosaic because of the “mosaic” of protein molecules embedded in a lipid bilayer. The mosaic is fluid as most of the proteins and lipid molecules drift in a lateral direction at the rate of about two microns/minute. Your professor graphically refers to proteins floating in a sea of lard!

Question 2

review

Answer 2

• The membrane is stabilized by an extracellular matrix and by an intracellular cytoskeleton
• lipid bilayer. It consists of hydrophobic tails sandwiched in between hydrophilic heads that point toward the cellular cytoplasm or toward the watery outer environment.

Question 3

selective permeability

Answer 3

• describes the plasma membrane’s ability to allow certain molecules to pass through more easily than others. Some molecules are completely blocked. The
  plasma membrane is structured so as to promote selective permeability of substances:

Question 4

Which of the following would increase membrane fluidity?

a. having a greater proportion of unsaturated lipids in the lipid bilayer
b. having a greater proportion of saturated lipids in the lipid bilayer
c. a relatively high protein content in the membrane
d. a relatively low cholesterol content in the membrane

Answer 4

• a. having a greater proportion of unsaturated lipids in the lipid bilayer

Question 5

The fluid mosaic model proposes that the plasma membrane is

Answer 5

• a non-rigid bilayer of phosphorylated lipids with embedded proteins

Question 6

Which of the following is not a role of the plasma membrane?

a. The plasma membrane defines the boundaries of a cell.
b. The plasma membrane regulates the passage of molecules into and out of the cell.
c. The plasma membrane manufactures proteins.
d. The plasma membrane functions in cell recognition.

Answer 6

c. The plasma membrane manufactures proteins

Question 7

The plasma membrane is more readily permeable to which molecule?

Answer 7

• a steroid hormone

Question 8

Proteins in the membrane

Answer 8

• can transverse the membrane completely or partially, or simply be bound to the exterior surface of the membrane

Question 9

True or false?
Although the plasma membrane is “fluid” in the sense that it is not rigidly held together, the molecular forces present prevent migration within the membrane of individual components such as phospholipid molecules or proteins.

Answer 9

• false