What is Cell Cycle? What are the Different Phases of a Cell Cycle?

Complete lifecycle of a cell is called the cell cycle. In other words, it is an orderly series of changes that occurs in a cell by which the cell duplicates its genetic material along with that it duplicates other content; finally, it divides and results in the formation of two daughter cells. An interphase occurs between two phases. During interphase, a cell grows in size and prepares itself for the next division. Interphase is also the most active phase of a cell cycle. During this phase, the metabolism activity of cell increases and a series of changes occur during the same phase. However, these changes are not visible under the microscope. That is why some scientists have termed interphase as a Resting Phase. Howard and Pelc -- two scientists have classified interphase into three sub-stages:




 The time taken by the cell to divide is known as generation time. For yeast, generation time is about 90 minutes.

(I) G1 Phase / Pre-DNA synthesis phase / Post-mitotic phase:
-- Maximum growth of the cell along with an increase in the size of the nucleus is seen.
--  It is the longest duration of the Interphase
-- During this phase, there is synthesis of nucleotides / amino acids / energy-rich molecules (ATP)
-- Polymerisation of nucleotide results in RNA synthesis.
-- RNA polymerase becomes active along with the enzymes for DNA synthesis.an
-- Synthesis of amino acids, which are involved in histone protein synthesis.

(II) S-Phase (DNA Synthesis Phase):

-- DNA duplication / replication takes place.
-- Chromosome consists of two chromatids
-- Centriole duplication occurs in the cytoplasm
-- Amino acids polymerize and form histone proteins
-- Assembly of kinetochore subunits
-- The duplicated chromosomes will not appear during this phase and that's why this phase is known as INVISIBLE PHASE


G2-Phase / Post-DNA synthesis phase / Pre-mitosis phase

-- Known as the second growth phase.
-- Cell size increases
-- Nucleus size increase
-- RNA synthesis takes place
-- Protein synthesis takes place
-- Duplication of most of the cell organelles (along with the division of mitochondria and division of plastids)
-- Biochemicals are formed for the synthesis of spindle fibres.
-- Tubulin protein synthesis takes place.
-- It is also signified by the synthesis of some protein kinases for the regulation of cell division