Question

Your friend comes to you in a panic. He was purifying extracts from interphase cells as well as mitotic cells. Unfortunately, the labels came off his tubes and he cannot tell which extract is from which cells. You do an experiment in which you add a small amount of each extract to fluorescent microtubules you have polymerized in vitro, and then use video microscopy to follow the behavior of individual microtubules in the reaction over time. Your results are shown in the graphs in Figure below.

https://d2vlcm61l7u1fs.cloudfront.net/media%2F125%2F1252748d-2227-4dc0-8fbc-fdaabcf1d708%2FphpEKLGPx.png

Answer 1

Microtubules polymerize and attach to the centromere of chromosomes in the metaphase of mitosis. They then pull the chromatids apart. Polymerization is thus an attribute of mitosis' initial stages. In later stages microtubules undergo depolymerization pulling the chromatids towards poles. Hence Extract 1 graph which shows polymerization first followed by depolymerization helps us identify that extract 1 is undergoing mitosis whereas extract 2 is in interphase.