Cell Division and Cell Division
Growth and reproduction are characteristics of living cells.
All cells reproduce by dividing into two with each parental group giving rise to two
daughter cells each time they divide. These newly formed daughter cells grow and
divide giving rise to a new cell population.
The processes like cell division, DNA replication, and cell growth, have to take place in a
coordinated way to ensure correct division and formation of progeny cells containing intact
genomes.
Cell cycle - The sequence of events by which a cell duplicates its genome, synthesises the
other constituents of the cell and eventually divides into two daughter cells is termed cell
cycle.
The process by which new cells are formed from the pre-existing cells is known as cell
division.
PHASES OF CELL CYCLE –
- These cells divide approximately once every 24 hours, of which cell division
proper (M-Phase) last for 1 hour while the remaining is interphase.
- However, the duration of cell cycle can vary from organism to organism and also
from cell type to cell type. Yeast for example, can progress through the cell cycle
in only about 90 minutes.
- The cell cycle is divided into two basic phases:
l Interphase
l M Phase (Mitosis phase)
-The M Phase represents the phase when the actual cell division or mitosis occurs and
the interphase represents the phase between two successive M phases.
-The M Phase starts with the nuclear division, corresponding to the separation of
daughter chromosomes into two daughter nuclei(karyokinesis) and usually ends with
division of cytoplasm and separation of the two daughter nuclei into two daughter cells
(cytokinesis).
- INTERPHASE –
. Interphase is the most active stage in the cell where the cell prepare itself for cell
division by undergoing cell growth and DNA replication in an orderly manner.
. The interphase is divided into three further phases:
l G1 phase (Gap 1) l S phase (Synthesis) l G2 phase (Gap 2) |
. G1 phase corresponds to the interval between mitosis and initiation of DNA replication.
During G1 phase the cell is metabolically active and continuously grows but does not
replicate its DNA.
. S or synthesis phase marks the period during which DNA synthesis or replication takes
place. During this time the amount of DNA per cell doubles. However, there is no
increase in the chromosome number i.e., the number of chromosomes remains the
same. In animal cells, during the S phase, DNA replication begins in the nucleus, and the
centriole duplicates in the cytoplasm.
. During the G2 phase, proteins are synthesised in preparation for mitosis while cell
growth continues.
. Some cells in the adult animals do not appear to exhibit division (e.g., heart cells) and
many other cells divide only occasionally, as needed to replace cells that have been lost
because of injury or cell death. These cells that do not divide further exit G1 phase to
enter an inactive stage called quiescent stage (G0 ) of the cell cycle (Cells in this stage
Cell cycle of human cell in
culture
