Cell Cycle and Cell Division Test - 3

S phase marks the phase of DNA replication and chromosome duplication. In this phase increase in the amount of DNA takes place. No synthesis of proteins or RNA takes place.

Before the completion of Mitosis reapperance of nuclear membrane takes place along with formation of nucleolus so that the cells bocemo separate enetities after cytokinesis but having same chromosome number as parent cells.

It is the stage of cell cycle during which the cells remain metabolically active and do not divide due to absence of mitogens and energy producing compounds.

Cell division consists of karyokinesis and cytokinesis. During karyokinesis division of chromosomes takes place and during cytokinesis division of cytoplasm takes place. Ultimately the cell divides into two halves.

The resulting two identical copies of DNA are connected to each other at the centromere. Each copy is called a chromatid. A chromosome, before cell division is formed of one chromatid while it is formed of two chromatids after cell division.

In plants, cytokinesis or division of cytoplasm occurs due to cell plate formed out of deposition of materials along the equatorial region of cell but in animals cytokinesis occurs due to formation of cleavage furrow in the middle cell membrane.

Cycline and CDKs  can modify various protein substrates involved in cell cycle progression. Cancer results due to mutations of these proteins leading to uncontrolled cell divisions.

S-phase of M-stage is called as invisible phase of cell cycle because during this phase synthesis of DNA takes place which is not visible to the naked eye. There is only imbalance of Nucleoplasmic ratio.

Karyokinesis is followed by cytokinesis but some times cytokinesis is not followed by karyokinesis which leads to the establishment of multinucleate condition. This type of cells are called as coenocytes.

The mechanism of distributing chromosomes to the daughter cells is called astral division. This kind of division occurs in animal cells.