19. In most cells, the concentration of monomeric actin is between 50-500 ??, ho
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19. In most cells, the concentration of monomeric actin is between 50-500 ??, however the measured critical concentration of purified G-actin is below 1 ??. Given this, the expectation is that most G-actin in the cell would readily polymerize into filaments. What keeps this from happening? (5 pts) 20. You are culturing human fibroblasts. When you immunostain the cells using an ER (endoplasmic reticulum) marker, you find that instead of extending throughout the cytoplasm normally, the ER appears to be collapsed near the nucleus. What could explain why theE extended into a meshwork of inter-connected membrane tubules? Give two possible explanations. (6 pts)Explanation / Answer
19) Cytochalasin is a drug which binds to the (+) ends of the G-actin and prevents the F-actin protein subunits from forming polymers inside the cell.
20)1)Fibroblast activation factor(FAF) is an enzyme which is secreted in the fibroblast cells. It breaks down the polypeptides after the proline on the N-terminal side. It if highly activated in the cancer stages of the cells. It leads to the loss of the ER membranes during the stages of apoptosis and stress of the ER which causes the activation of the ER chaperone/BIP, ATF6 proteins. The merging of the golgi and ER membranes during protein sorting causes the accumulation of these vesicles near the nuclues instead of getting aggregated in the nucleus.
2)Addition of benzopyrene carcinogen to the fibroblasts indicates the formation of vesicles of ER near the nucleus and these complexes are named as paranuclear complexes.
The staining can also be done with quinacrine intercalating dye to observe the formation of the vesicular complexes near the nucleus of the cell.
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