20- Discuss the compositional asymmetry of cell membranes (with specific example
ID: 149636 • Letter: 2
Question
20- Discuss the compositional asymmetry of cell membranes (with specific examples) and indicate how this asymmetry is maintained. 21-Some cells use their cortical network to restrain the diffusion of membrane proteins. What other function(s) does the cell cortex play? 22-Discuss the composition and importance of the Glycocalyx. 23- Figure 3 below represents the data for the mobility study of three different proteins (X, Y, and Z) using the fluorescence recovery afer photobleaching (FRAP) technique. Use these data to range the proteins according to their diffusion rate. b. PROTEIN x Which of these proteins is probably an anchored protein? Explain. PROTEINY PROTEIN Z bleach bleach bleach 5 time time time Figure 3 24-Consider the apical location of a particular protein (protein A) expressed in epithelial cells, as illustrated in Figure Figure 4A bellow. Which type of defect is likely to cause the redistribution of that protein around the entire cell as shown in Figure 4B?Explanation / Answer
20. The cell membranes have different composition on both sides of the membrane. Phospholipids are distributed asymmetrically in the lipid bilayer. Proteins are in different position in the membrane.
Flippase moves lipids to the inner monolayer and floppase to the outer monolayer, whereas scramblases exchange lipids between both monolayers. The asymmetry is maintained because "flip-flop" movement is rare in the cell membranes. Like, sphingolipids are not exchanged between monolayers and gets positioned in the monolayer where these were synthesized.
21. In mitosis, cell cortex helps in mitotic cell rounding. In cytokinesis it produces a myosin rich contractile ring to generate two daughter cells through cell division.
22. Glycocalyx is made up of glycoprotein and glycolipid. It acts as a backbone molecule for support. They help in cell-cell recognition, intercellular adhesion and communication.
23. FRAP is a method to determine the kinetics of diffusion through cells. According to the graphs, protein X has the maximum diffusion rate which shows a sharp increase, and protein Y has the lowest diffusion, as it has very low fluorescence in it’s bleached area, whereas protein Z has the moderate diffusion rate.
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