Study Question Sets for Exam 1
Study Question Set 4
Membrane Structure 1, 2 & 3
- Illustrate or describe our current concept of the structure of a
cell membrane, indicating the organization of membrane lipids and the various
ways in which proteins can associate with the membrane.
- Distinguish between classical integral membrane proteins and peripheral
proteins in terms of the ease with which each type is removed from a membrane.
Explain why methods for removing the two types of proteins from membranes
are different. Be thorough.
- Indicate the limitations of the Robertson/Danielli-Davson
model of membrane structure, as compared to the Singer model, in accounting
for the dynamic features of cells.
- The lipid bialyer is very fluid and integral proteins are
able to move laterally through the lipid bilayer with relative ease. Do
these proteins also "bob" up and down in the lipid bilayer, with one end immersed
within the bilayer instead of protruding through it? If so,
what keeps them from dropping into the cytoplasm or popping out of the bilayer?
If not, why not? (A student-generated question.)
- Why did red blood cells prove very useful for early
studies of the protein composition of membranes?
- What is meant by the term "amphipathic"? How does amphipathicity
contribute to the formation of a stable membrane structure?
- What role does water play in determining the molecular organization
of cell membranes? Explain.
- The nature of scientific investigation is such that "good
science" can result in incorrect interpretations or conclusions because of
a lack of complete information. Explain how the limitations of our knowledge
of the diversity of protein structure and properties led Danielli and Davson
to propose that membrane proteins lie exclusively at the protoplasmic and
extracellular surfaces of membranes.
- Describe an experiment using cells of different species, Sendai
virus, and fluorescent antibodies which provides support for the Singer model
model of membrane structure.
- The most common structural organization of the membrane-spanning
portion of a single-pass integral membrane protein is an alpha helix. How
does this organization allow regions of protein structure to cross the lipid
bilayer of a membrane?
- Indicate the importance of early work on bacteriorhodopsin to the
development of the Singer model of membrane structure.
- Plasma cells have surface receptors for binding the foreign antigen
that they are differentiated to make antibody against. The antigen binding
sites are spread all over the surface of "virgin" cells, but after
antibody binding occurs, the binding sites, with their bound antibodies, aggregate
into clusters (called patches). What does this "patching" tell us
about cell membranes that is incompatible with the Robertson/Danielli-Davson model?
- What is a "lipid raft"?
- What feature(s) of a plasma membrane protein determine whether or not that
protein will reside in a lipid raft? Explain.
- What is FRAP? Explain how FRAP can be used to study the relative
mobilities of different membrane components.
- Defend or refute the following statement, citing examples to support
your thesis. Be thorough.
"Membrane proteins and membrane lipids are totally independent entities."
- Describe the steps involved
in preparing a specimen for examination by freeze-fracture techniques.
- What is the "replica"
we examine in freeze-fracture microscopy?
- What type of microscope do we use to examine freeze-fracture replicas? nbsp; How are we able to see the important featurs of the replica?
- What can freeze-fracture tell us about membrane proteins?
- Lipids extracted from cell membranes can be used to create artificial lipid
bilayers.
- Describe the fate of bacteriorhodopsin when it is mixed with
such lipids being used for artificial bilayer (or liposome) formation.
- Compare the behavior expected of bacteriorhodopsin to that one would expect
under the same conditions for serum antibodies, which are hydrophilic, globular
glycoproteins that circulate in the blood or permeate into interstitial
fluids.
- How would one use freeze fracture to verify one's predictions in (a) experimentally?
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