G1 -phase (first growth and gap phase pre-synthetic phase, post mitotic phase) is the longest phase of cell cycle, in which cell and its nucleus grow in size. There is synthesis of biochemicals like RNAs, protein, enzymes for DNA synthesis, amino acids for histone formation, nucleotides and ATP.
S-phase (synthetic phase) : During this phase, DNA of each chromosome replicates followed by synthesis of histones. Each chromosome undergoes replication producing two chromatids. It is also known as invisible stage of M-phase. G2 -phase (second growth phase or gap phase, post synthetic phase, premitotic phase) : During this phase, synthesis of protein and RNA take place. Cell organelles increase in number and a protein called tubulin is formed.
M-phase is the phase of cell division. Cell division consists of nuclear division karyokinesis and protoplast division or cytokinesis. It is of three type-
amitosis, (ii) mitosis and (iii) meiosis.