Question

1. Explain how cell division is organized by the cytoskeletal elements in an animal cell.  Include in your answer the roles and structures of each of the cytoskeletal elements (microtubules, actin filaments, and intermediate filaments) and the roles and mechanisms of the various motor proteins.  Organize your answer by cell cycle stage, including G2, prophase, metaphase, anaphase, telophase, and cytokinesis.

2. Plant cells do not have centrioles, yet they can still perform cell division. How is this possible?

Answer 1

1. Cytoskeleton as the name suggest it functions as a skeletal support for a cell. There are three kinds of specialized proten structures which assist the skeletal function collectively called cytoskeleton. The three elements are-

Microtubules: It is consist of alpha and beta tubulin units. spindle fibre which help in chromosome separation are composed by the microtubules. The microtubule dirmers can easilly assemble and disassamble to form the spindle fibres.

Acitin filaments: It is composed by the actin proteins and play a major role in cytokinesis by forming contractile ring.

Intermediate Filaments: Unlike the microtubules and actin flament, the intermediate filament is made up of varieties of proteins respect to the cell type. It is also differ from the others by its mechanical strenght. It actually give the cell the mechanical support to retain its shape and integrity and to perfor the other cellular function including organelle locomotion.

In the cell cycle At the late G2 phase microtubules are start to produce. in the prophase they start to assemble to generate spindle fibres. During metaphase, complete spindle are formed and attached to the kinetochore proteins of the chromsomes which were already arranged in the equitorial zone. When anaphase start, spindle pulls the chromosomes from both poles to sseparate  two chromatids and move them in two opposite poles. After the completion of the chromatid separation of chromatids, microtubules start to disassemble and this phase is called telophase. cytokinensis is the division of cytoplasm to form two daughter cells. After the completion of telophase, cytokinesis takes place. For cytokinesis, a necessary element is contractile ring and its squeez the cell in the middle like a camera diaphragm and separate the cytoplasm. The ring is consisted of actin filaments. unlike microtubules and actin filaments, Intermediate filaments is always present with in the cell to keep the cellular integrity.

2. Plant cells do not have centrioles but instead they have the microtuble clusters at the two opposite poles which help in spindle formation and perform cell division.

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