Answers
Purpose of cell cycle
It is the process by which cells in multicellular organisms divide helping the organisms to grow and duplicate genome for reproduction.
Cel cycle is the sequence of events by which a cell duplicates its genome, synthesises constituents of cells and then divides into two daughter cells is called as cell cycle.
Phases in cell cycle are
M PHASE -
The phase where actual division or mitosis occurs. Karyokinesis and cytokinesis occurs in this phase.
Interphase - phase between two successive M phases. Interphase is further divided into 3 more phases
G1 phase - interval between mitosis and initiation of DNA replication.
G2 phase- proteins are synthesised for mitosis
S phase or synthesis phase - period during which DNA synthesis or replication occurs.
M PHASE is divided into 4 more stages
Prophase - 1st phase of mitosis. Follows S and G2 phase. Here chromosomal material condenses to form compact chromosomes.
The centriole which duplicated during S phase of Interphase begins to move towards the opposite poles. Initiation of assembly of mitotic spindle, microtubules, proteinacious compounds of cytoplasm help in this process
Metapha se - total disintegration of nuclear envelope, chromosomes are spread throughout the cytoplasm. Chromosomal condensation is complete. Chromosomes in this phase have two sister chromatids held at the centromere. Kinetochores appear these are the site of attachment of spindle fibres to chromosomes.
Here all the chromosomes lie at the equstor. Hence chromosomes are connected by kinetochores to spindle fibres in one pole and centromere are connected by kinetochores to spindle fibres at opposite pole.
Anaphase - each chromosome at Metapha se plate will split into two daughter chromatids. And migrate to opposite poles.
Telophase. - chromosomes that migrated to poles deconndense and lose their individuality
And chromatin material clumps at the two poles. Nuclear envelope is formed around chromosomes and nucleus, golgi complex and ER reform.
