Question
Membrane Potpourri. Explain each of the following observations as succinctly as possible. a) Proteins A and B have a molecular weight of 33,000 and consist
of a single polypeptide chain with 240 hydrophilic amino acids and 60 hydrophobic amino acids, yet protein A is an integral membrane protein and protein B is a soluble protein.
b) When a photobleaching experiment similar to that described in Figure 7-11 is carried out using plasma membranes from myoblasts (precursors to muscle cells) with fluorescently tagged surface glycoproteins, it takes much for the dark, nonfluorescent spot to become fluorescent again than when phospholipids are labeled with a fluorescent dye. Moreover, only 55% of the protein fluorescence eventually returns to the laser-bleached spot.
c) In the legs of reindeer, the membranes of cells near the hoof have a higher
d) Most of the agents used in anesthetics in medicine are non-polar and act by increasing the fluidity of the lipid bilayers of cellular membranes to the extent that the transmission of nerve impulses is disrupted and sensations of pain are eliminated.
Explanation / Answer
a). Two proteins with same molecular wieght and single polypeptide chain containing 240 hydrophilic amino acids and 60 hydrophobic acids, need not to be the same proteins. - There will be difference in the sequence alignment of the amino acids, and folding differs for both. - There are many hydrophillic and hydrophobic amino acids, and both proteins may have different amino acid composition. - In the case of soluble protein, the hydrophobic amino acids may fold inward, imparting solubility to the protein. -Integral protein have specific domains, that attach with the membranes. b) It takes much time for nonfluorescent spot to become fluorescent again because the content of uptake is more compared to others. c). It is because the temperature of body tissues at the hooves, generally will be low than center of the body. To maintain fluidity, membranes at lower temperatures must contain higher percentage of unsaturated fatty acids. A percent of unsaturated fatty acids will lower the melting point of lipid mixtures. d). Anesthetics are non-polar and act by increasing fluidity of the lipid bilayers of cellular membranes. Due to this the permeability of cellular membrane will increase and the anesthetics will bindto the sodium channels, there by preventing the nerve transmission.