The Cell Review
Cell Membrane Structure and Function
What are the main molecular components of cell membranes?
Composed of phospholipids (phosphate group at end hydrophilic, fatty acids at tails hydrophobic) and
proteins (many glycoproteins and glycolipids – carbohydrates attached).
What are some of the less abundant molecules?
Cholesterol – keeps it strong and together.
Describe and discuss the “fluid mosaic model” of membranes?
Phospholipid bilayer: Two layers of phospholipids. Proteins are embedded throughout the phospholipids.
(Some proteins are attached to microtubules and can’t move – makes for more mosaic/fluid nature rather
How are the phospholipids arranged in the membrane and what are the reasons and
significance of that?
The hydrophobic tails in center of membrane – so can interact with water.
Hydrophilic parts on the inside and outside edges.
How are the glycoproteins oriented?
Carbohydrates are attached to the outer portion of the proteins. These proteins are hydrophilic.
What are the functions (other than structural) of the proteins and glycoproteins in the
They are essential in communication in the membrane.
What is the significance of the fact that some membrane proteins are anchored to
This gives rise to the membrane’s mosaic nature.
Why is the membrane considered to be semipermeable?
Few molecules can freely enter/leave the cell. The semi permeable membrane allows communication
between the cell and its external environment and also maintains the environment on the inside.
Distinguish between isotonic, hypotonic, and hypertonic solution. How would a cell (such as
a red blood cell) be affected by being placed in each of these?
Isotonic: Same concentration of water on the inside and outside of the cell. No effect.
Hypotonic: Less water in the blood cells, therefore the water will rush in and the cells will swell up and
Hypertonic: More amount of water on the inside of the cell, it will rush out and the cells will shrivel up
Define and explain: diffusion, facilitated transport, active transport. What is the basis for
each, and how do are the similar and what makes them unique?
Diffusion: Water (carbon dioxide and oxygen can also diffuse across membran