Cytokinesis in animal cells ________________
(a) requires ATP.
(b) leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane.
(c) is often followed by phosphorylation of integrins in the plasma membrane.
(d) is assisted by motor proteins that pull on microtubules attached to the cell cortex.
(a) All cell movement requires ATP, and in cytokinesis actin and myosin molecules are moving relative to one another to cause contraction of the contractile ring. The myosin is an ATPase that hydrolyzes ATP to power this movement. The assembly of the contractile ring requires a general rearrangement of the filaments in the cell cortex. The contractile ring in animal cells disassembles completely after mitosis, leaving no trace [choice (b)]. Phosphorylation of integrins (which weakens the hold of these transmembrane proteins on the extracellular matrix, thereby allowing cells to round up) generally precedes cytokinesis and is part of the general rearrangement of cell structure that accompanies cell division [choice (c)]. Microtubules do not have an important role in animal cytokinesis [choice (d)].
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