Introduction
Ability to grow and reproduce is the fundamental property of all living
organisms. Both multicellular and unicellular organisms start their life
or arise from a single cell, i.e., fertilized egg or zygote. These
organisms grow by addition of new cells which arise by division of pre-
existing cells. Thus, cell division or cell reproduction maintains the
continuity of life. Cell division is defined as a process in which a single
parent cell divides into two daughter cells. The two daughter cells are
identical to each other and also to the parent cell. These two daughter
cells grow, attain maturity and then divide again into two daughter
cells. This process continues and a single cell divides into million cells
which form the body of organisms. Before dividing into two daughter
cells, a cell goes through different phases and different stages which
we would study in this chapter. We would look into the different
processes that occur during the cycle of growth and division and
would deeply study each and every preparation, the cell does for
undergoing growth and division. This chapter would help us to answer
some of the simple questions like what is the significance of cell
division, why is it important?
CELL CYCLE
The sequence of events by which a cell duplicates its genome,
synthesizes other constituents of the cell and eventually divides
into two daughter cells is termed as cell cycle. It is a genetically
controlled series of changes that occur in a newly formed cell by
which it duplicates its contents, undergoes growth and division to
form two daughter cells.
When a cell enters the cell cycle, it goes through various phases
which prepare it for cell division. Synthesis of DNA, duplication of
cell
Organelles, synthesis of various proteins are the
various requirements
Of a cell which is about to enter mitosis. The cell
synthesizes these constituents in a sequential pattern
to ensure that proper division and distribution of
components occurs within the two daughter cells, This
, that proper intact genome enters the two daughter cells
and formed are functionally and structurally intact, The
daughter cells then grow and again at maturity undergo
cell division,
Growth is a continuous process which occurs throughout the life of a
cell but duplication of organelles, DNA replication etc. occurs during a
specific stage of the cell cycle.
Thus, the cycle is the period (time) between the formation of
new daughter cells and their further division,
PHASES OF THE CELL CYCLE
Cell cycle basically consists of two phases namely
Interphase
M or Mitotic phase
Interphase is a phase between two successive M phases, where the
cell prepares itself for cell division. It is a biosynthetic phase in which
the cell duplicates its organelles and replicates its DNA (genetic
material). It institutes more than 95% duration of the cell cycle.
M phase or Mitosis is the phase where the actual cell division occurs. In
this phase, the cell utilizes the constituents formed during interphase
and divide into two daughter cells.
Period of cell cycle varies from organism to organism and also from
cell to cell, e.g., a yeast cell divides once in 90 minutes, a typical
human cell divides approximately every 24 hours.
INTERPHASE
It is a non-dividing, growing phase of the cell cycle, where the cell
prepares itself for division. It represents the most active stage of the
, cell cycle where both cell growth and DNA replication occur in an
orderly manner. It is the period of intense growth and synthesis in
which a cell stocks all the biomolecules required during cue division. It
is called the resting phase because there is no apparent activity
related to cell division rather, it deals with the changes that occur in a
cell and the nucleus, before it enters into cell division. It is further
divided into three stages:
G1 Phase
G1 phase is the interval between mitosis and initiation of DNA
replication. In this phase, cell does not synthesize or replicate DNA but
remains metabolically active. The cell grows in size continuously and
synthesizes nucleotides, ATP, proteins, amino acids, RNA etc. (required
during S phase). Most of the organelles duplication occurs in this
phase. The length of the G1 phase varies from one cell to another. If a
cell divide frequently, then it has a shorter G1 phase and if a cell does
not divide frequently, then it has begun G1 phase.
Some cells in an adult animal do not divide, e.g., nerve cell, whereas
many cells divide occasionally just to replace the cell host due to injury
or cell death. Such type of cells remain in Go phase.
Go Phase: The non-dividing cell enters the quiescent stage or Go stage
of the cell cycle. In this phase, the can remains metabolically active
but do not proliferate unless they are called on to do so.
S Phase
•S or synthesis phase is a phase in which synthesis or replication of
DNA takes place. It is the phase in cell doubles its DNA. For example, if
the initial amount of DNA is denoted by 2 C. Then after the S phase the
amount of DNA would become 4C, the amount of nucleic acid, i.e.,
DNA (genetic material) but the number of chromosomes remains the
same. For example. If a diploid ceil has 2n number at G1 phase, then
even after S phase, the number of chromosome would remain 2n. The
DNA molecule acts as a template to synthesize new DNA molecule.
Ability to grow and reproduce is the fundamental property of all living
organisms. Both multicellular and unicellular organisms start their life
or arise from a single cell, i.e., fertilized egg or zygote. These
organisms grow by addition of new cells which arise by division of pre-
existing cells. Thus, cell division or cell reproduction maintains the
continuity of life. Cell division is defined as a process in which a single
parent cell divides into two daughter cells. The two daughter cells are
identical to each other and also to the parent cell. These two daughter
cells grow, attain maturity and then divide again into two daughter
cells. This process continues and a single cell divides into million cells
which form the body of organisms. Before dividing into two daughter
cells, a cell goes through different phases and different stages which
we would study in this chapter. We would look into the different
processes that occur during the cycle of growth and division and
would deeply study each and every preparation, the cell does for
undergoing growth and division. This chapter would help us to answer
some of the simple questions like what is the significance of cell
division, why is it important?
CELL CYCLE
The sequence of events by which a cell duplicates its genome,
synthesizes other constituents of the cell and eventually divides
into two daughter cells is termed as cell cycle. It is a genetically
controlled series of changes that occur in a newly formed cell by
which it duplicates its contents, undergoes growth and division to
form two daughter cells.
When a cell enters the cell cycle, it goes through various phases
which prepare it for cell division. Synthesis of DNA, duplication of
cell
Organelles, synthesis of various proteins are the
various requirements
Of a cell which is about to enter mitosis. The cell
synthesizes these constituents in a sequential pattern
to ensure that proper division and distribution of
components occurs within the two daughter cells, This
, that proper intact genome enters the two daughter cells
and formed are functionally and structurally intact, The
daughter cells then grow and again at maturity undergo
cell division,
Growth is a continuous process which occurs throughout the life of a
cell but duplication of organelles, DNA replication etc. occurs during a
specific stage of the cell cycle.
Thus, the cycle is the period (time) between the formation of
new daughter cells and their further division,
PHASES OF THE CELL CYCLE
Cell cycle basically consists of two phases namely
Interphase
M or Mitotic phase
Interphase is a phase between two successive M phases, where the
cell prepares itself for cell division. It is a biosynthetic phase in which
the cell duplicates its organelles and replicates its DNA (genetic
material). It institutes more than 95% duration of the cell cycle.
M phase or Mitosis is the phase where the actual cell division occurs. In
this phase, the cell utilizes the constituents formed during interphase
and divide into two daughter cells.
Period of cell cycle varies from organism to organism and also from
cell to cell, e.g., a yeast cell divides once in 90 minutes, a typical
human cell divides approximately every 24 hours.
INTERPHASE
It is a non-dividing, growing phase of the cell cycle, where the cell
prepares itself for division. It represents the most active stage of the
, cell cycle where both cell growth and DNA replication occur in an
orderly manner. It is the period of intense growth and synthesis in
which a cell stocks all the biomolecules required during cue division. It
is called the resting phase because there is no apparent activity
related to cell division rather, it deals with the changes that occur in a
cell and the nucleus, before it enters into cell division. It is further
divided into three stages:
G1 Phase
G1 phase is the interval between mitosis and initiation of DNA
replication. In this phase, cell does not synthesize or replicate DNA but
remains metabolically active. The cell grows in size continuously and
synthesizes nucleotides, ATP, proteins, amino acids, RNA etc. (required
during S phase). Most of the organelles duplication occurs in this
phase. The length of the G1 phase varies from one cell to another. If a
cell divide frequently, then it has a shorter G1 phase and if a cell does
not divide frequently, then it has begun G1 phase.
Some cells in an adult animal do not divide, e.g., nerve cell, whereas
many cells divide occasionally just to replace the cell host due to injury
or cell death. Such type of cells remain in Go phase.
Go Phase: The non-dividing cell enters the quiescent stage or Go stage
of the cell cycle. In this phase, the can remains metabolically active
but do not proliferate unless they are called on to do so.
S Phase
•S or synthesis phase is a phase in which synthesis or replication of
DNA takes place. It is the phase in cell doubles its DNA. For example, if
the initial amount of DNA is denoted by 2 C. Then after the S phase the
amount of DNA would become 4C, the amount of nucleic acid, i.e.,
DNA (genetic material) but the number of chromosomes remains the
same. For example. If a diploid ceil has 2n number at G1 phase, then
even after S phase, the number of chromosome would remain 2n. The
DNA molecule acts as a template to synthesize new DNA molecule.
