1) What is: The number of centrosomes present during interphase? The number of c

Question

1) What is: The number of centrosomes present during interphase? The number of centrosomes present during metaphase? The number of kinetochores on each chromosome during mitotic prometaphase? The number of microtubules in a mitotic spindle?

2) At which mitotic stage:

a) The nuclear envelope is broken down but many of the chromosomes are not fully attached to the spindle microtubules

b) The new cell plate in a plant cell is beginning to form along with new nuclei

c) The nuclear envelope is still intact but the chromosomes have condensed

d) The kinetochores from both sister chromatids have attached to microtubules from opposite poles, but the sister chromatids are still attached and aligned midway between the poles

Explanation / Answer

Answer:

1.a. Centrosomes are an important cell cycle regulator as well as microtubule organizing center (MTOC) of the animal cell. During the interphase, the centrosomes replicate and form two centrosomes. Each centrosome with two centrioles.

1.b. There are two centrosomes present during metaphase which are located at the opposite ends(poles) of the cell.

1.c.Kinetochores are proteinaceous structures present on chromosomes. This is the major point of contact between microtubules of the mitotic spindle and chromosomes. This helps in the proper chromosome segregation. During the prometaphase, centromere of each chromosome develops two kinetochores.

1.d. Mitotic spindle apparatus consists of the microtubules. The three classes of microtubules are kinetochore microtubule, Interpolar microtubules and  Astral microtubules. These structures help to control the chromosome movement during mitosis. Each mitotic spindle fiber consists of single microtubule with tubulin subunits.

2.a. In prometaphase, the chromosomes are not fully attached to the spindle microtubules but the nuclear envelope is already broken down.

2.b.During the telophase, new cell plate starts to grow at the center which later develops into a cell wall during cytokinesis along with new nuclei.

2.c.This is the situation present in the early prophase. The nuclear envelope only starts to disintegrate but the chromosome has condensed.

2.d. This situation is present in the early anaphase, where the kinetochores from both sister chromatids have attached to microtubules from opposite poles. But sister chromatids are still attached and aligned midway between the poles.

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