The period between two consecutive cell divisions is called interphase. This state is called rest state. The nucleus in this state is called the metabolic nucleus.
Characterization of the interphase state
(i) CDK (Cyclin Dependent Kinase) compounds provide external stimulation in interphase state.
(ii) Various hormones and growth factors provide internal stimulation during interphase.
(iii) Various metabolic activities continue in the cell during this stage. As the nucleus increases in size and many reactions take place, it is called metabolic nucleus.
(iv) DNA, RNA and protein synthesis takes place in this stage. Hence it is called synthesis stage.
(v) Chromosomes are arranged as chromatin.
(vi) In this state, the cells have the necessary energy reserves.
(vii) Increase in cell volume is greatest in this condition.
(viii) Duplication of the DNA of the cell takes place, i.e. the monad turns into a dyad.
(ix) Centrosomes of animal cells divide.
(x) This phase takes 90-95% time.
3 subphases of interphase dasha
1. G1 Phase: Metabolically active cell growth phase is called pause-1 phase. This state is called antiphase. A cell that will no longer divide remains locked in the G1 subphase for a week or a year or forever. The characteristics of Birama-1 dasha are-
(i) Cell cycle starts in this state.
(ii) Whether a cell will participate in division depends on this stage.
(iii) Cyclin proteins, gabular proteins, fibrous proteins and RNA are produced in this subphase.
(iv) Cyclin protein binds to CDK and accelerates and regulates the process. CDK regulates the phosphorylation process.
(v) Enzymes are produced to make DNA and proteins.
(vi) Cytoplasm and nucleus of the cell increases in size.
(vii) Synthesis of various nucleotides and amino acids takes place.
(viii) In this state, the cells double in number.
(ix) Sub-phase takes 30-40% time.
2. Synthesis phase: The next phase after break-1 is called Synthesis phase or S phase or Synthesis phase. It is also called DNA replication. The characteristics of synthesis state are-
(i) Histone proteins and DNA are synthesized in subphase A.
(ii) The amount of DNA increases and doubles.
(iii) Physical elongation of chromosomes occurs and each chromosome divides to form two chromatids.
(iv) Subunits of kinetochore are formed at this stage.
(v) Division of centrosome occurs in animal cells.
(vi) At this stage inactive proteins are synthesized.
(vii) This sub-phase takes 30-50% time. Mammals take 7 hours in this state.
3. G2 Phase: The stage after synthesis phase is called pause-2. The features of Biram-2 are-
(i) Cell metabolism increases in this condition.
(ii) Histone proteins, non-histone proteins, tRNA, mRNA, rRNA etc. are synthesized.
(iii) Nucleus increases in volume as various elements are prepared.
(iv) In this phase the damaged DNA molecule is repaired.
(v) Two centrosomes arise from one centrosome. Centrosomes form microtubules. Microtubules form spindle fibers.
(vi) Cells enter mitosis from G2 phase with the help of maturation promoting factor (MPF).
(vii) Volume of nucleus and cytoplasm increases.
(viii) This sub-phase takes 10-20% time.
Importance of interphase state
(i) At this stage it is determined whether the cell will participate in the next division.
(ii) Energy required for cell division (ATP) is produced.
(iii) DNA replication takes place.
(iv) RNA synthesis and histone protein content increase.
(v) At this stage microtubules are formed which form centrosomes.
(vi) Centrioles are formed in animal cells in this state.
(vii) Cell division will not take place if there is no interphase state. A living organism will not form a body. As a result, new organisms will not be created.