 |  Biology, 6/e Author Dr. George B. Johnson,
Washington University
Author Dr. Peter H. Raven,
Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer,
Carleton College
Contributor Dr. Jonathan Losos,
Washington University
Membranes
Answers to Review Questions| Chapter 6 (p. 122)
1. A phospholipid is similar to a triglycerol, but has a phosphorylated alcohol in the place of the fatty acid on the third carbon of the glycerol molecule. Increasing the number of double bonds between carbons in phospholipid fatty acid chains would increase the fluidity of the membrane.
2. Proteins typically span cell membranes as multi-pass helices, which form protein channels, or as beta-barrels, creating pores in the membrane.
3. A cell hyperosmotic to its environment would have a higher concentration of solutes in its cytoplasm than the surrounding environment.
4. Both are forms of endocytosis, or taking extracellular materials into the cell. Phagocytosis employs the extension of pseudopods to take in comparatively large particulate material (such as a pathogen by a white blood cell); pinocytosis occurs when the cell invaginates to take in a volume of fluid containing desired microparticulate or molecular material.
5. In receptor-mediated endocytosis, a coated pit in the membrane contains a protein receptor. When triggered by the presence of a specific molecule, the pit closes over and traps the molecule within a vesicle.
6. Facilitated diffusion differs from simple diffusion in that specific carrier molecules are employed for movement across a membrane, and a saturation limit can be reached when no further diffusion can occur because all carrier molecules are in use.
7. Active transport is different from facilitated diffusion in that it is an energy-requiring (ATP-using) process capable of moving molecules against their concentration gradients, but similar in that it involves the use of carrier proteins.
|
|
2002 McGraw-Hill Higher Education