You are interested in understanding more about the contractile ring used during

Question

You are interested in understanding more about the contractile ring used during cytokinesis, and isolate a protein called FBPI that binds to formin and localizes it to the site of the cleavage furrow. What cytoskeletal element is important for the contractile ring? How does forming affect this cytoskeletal element? What motor is u sed to provide the contractile force necessary during cytokinesis? You examine FBPI protein and find that it is present in both interphase and M phase cells. However, when you look at the levels of phosphorylated FBPI as cells undergo the cell cycle, you get the results shown on the graph. Circle the stage of the cell cycle which correlates to the highest levels of phosphorylated FBPI. Name a molecule we discussed in class whose activity levels increase as cells enter mitosis and drop as cells exit mitosis. Propose a mechanism for how FBPI is phosphorylated, and how this phosphorylation affects the contractile ring. This mechanism needs to be consistent with the data above, and also what we know about how the cell cycle works. Please be as specific as possible.

Explanation / Answer

i) The cytoskeleton element in the contractile ring is filamentous actin and a motor protein myosin along with structural protein and regulatory protein.

Newly polymerised actin and pre existing actin initiate assembly of ring.

The contractile ring generates force and cleaves the cell into two

ii)Actin polymerisation is driven by formin

Formin nucleate linear , unbranched actin filaments

Rho-GTP activated at the equatorial cortex of the cell bind to formin and activates it.

iii)Contractile ring components generate force to seperate the cell.

Bipolar filaments of myosin use their motor activity to move along the two antiparallel actin filaments to slide apart each other and leads to constriction of contractile ring(pinching apart)

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