CELL CYCLE AND CELL DIVISION
CELL CYCLE
Cell cycle ( Howard and Pelc, 1953) is genetically controlled series of changes that occur
in a newly formed cell by which it supplicates ins contents,1undergoes, growth and
division to form two daughter .it consists of states or periods, a long nondividing growth
I-phase and a short dividing M-phase. Both have substages. I-phase represents
interphase.
The regular sequence of G1, S, G2 ( interphase) and M phase ( mitotic phase) is called
the cell cycle.
Interphase is called „resting stage”, but it is in fact a period of great activity. Three
important process, which are preparatory to cell division, take place during interphase.
Thus it is also known as preparatory phase. These processes are
- Replication of DNA along with the synthesis of nuclear proteins such as the
histones
- In animal cells, duplication of centriole takes place by the outgrowth of daughter
centrioles from the parent centrioles, which are at right angle to each other.
- Synthesis of embryo rich compounds, which provide energy for mitosis, and
synthesis of proteins at the end of interphase states or periods, a long non -dividing
growth I-phase and a short dividing M-phase. Both have substages. I-phase represents
interphase.
The regular sequence of G1, S, G2 ( interphase) and M phase ( mitotic phase) is called
the cell cycle.
Interphase is called „resting stage”, but it is in fact a period of great activity. Three
important process, which are preparatory to cell division, take place during interphase.
Thus it is also known as preparatory phase. These processes are
- Replication of DNA along with the synthesis of nuclear proteins such as the
histones
- In animal cells, duplication of centriole takes place by the outgrowth of daughter
centrioles from the parent centrioles, which are at right angle to each other.
- Synthesis of embryo rich compounds, which provide energy for mitosis, and
synthesis of proteins at the end of interphase
Interphase ( L.inter-in between, Gk-phase-stage) is intermitotic stage of cell division in
which a series of changes occur in newly formed cell and nucleus undergoes certain
, changes to be fit for division. Non dividing state of mature cell or nucleus is called
interphase. It is also called energy phase.
Interphase of dividing cell has been classified into three subphases -G1- Phase, S-phase
and G2-phase
G1-phase
G1 phase is also known as first growth phase or post mitotic gap phase. It is the longest
phase of cell division. In this phase different types of RNA (mRNA, tRNA, rRNA) and
proteins are synthesized.
All cell organelles ( ER, mitochondria, Golgi complex, ribosomes, plasmid in plant cell)
multiply. The duration of G1 Phase varies from cell to cell. It is shorter in frequently
dividing cells. G1 phase cell has three options.
a) Continuous cycle and enter S phase
b) Stops cell cycle and enter quiescent phase or g0 phase
c) Stops cell cycle and undergoes cell differentiation
The deciding factor for above option are availability of mitogen and energy rich
compounds. This point is called check point .
S-phase
S-phase is known as synthetic phase. In this stage replication of DNA takes place by the
synthesis of histones. As a result each chromosome under goes replication producing two
chromatids. Each chromosome carries a duplicate set of genes. A haploid cell (n)
, becomes diploid (2n) and a diploid cell (2n), thus becomes tetraploid (4n) at the end of S-
phase. Repairing of damaged DNA also takes place.
G2-phase
G2 is also called second growth phase or pre-mitotic gap phase. In this phase synthesis of
DNA stops and synthesis of RNAs and proteins continues. All cell organelles multiply
and spindle formation takes place. It lasts for 2-5 hours in most cells. Some proteins
formed in this phase cause condensation of chromosomes to initiate mitosis
G0-phase
The phase in which cells fail to divide further ( do not undergo S-phase after G1-phase)
and undergo differentiation is known as G0 phase or quiescent stage. It occurs due to
non-availability of mitogen and energy rich compounds. The cells remain metabolically
active, grow in size and differentiate for particular function after attaining a particular
shape.
However some cells remain in undifferentiated state as reserve cells. They may proceed
with cell division when required e.g. fibroblasts; it helps in healing of wounds and grow
and divide again.
M-phase
The process of cell division is found to be essentially the same in all living organism and
the events are chiefly centered in the nucleus. Three type of cell divisions have been
distinguished:
- Amitosis or direct cell division
- Mitosis or indirect cell division
- Meiosis or reduction division
Mitosis and meiosis are the two major types of cell division. The basic stage in both the
types of divisions are almost identical.
Amitosis is a direct division characterized by the splitting of nucleus followed by that of
cytoplasm.
Mitosis is a somatic cell division which takes place in vegetative cells. It maintains the
chromosome number.
Meiosis is a reduction division, occurring in the reproductive cells. The chromosome
number are reduced to half.
CELL CYCLE
Cell cycle ( Howard and Pelc, 1953) is genetically controlled series of changes that occur
in a newly formed cell by which it supplicates ins contents,1undergoes, growth and
division to form two daughter .it consists of states or periods, a long nondividing growth
I-phase and a short dividing M-phase. Both have substages. I-phase represents
interphase.
The regular sequence of G1, S, G2 ( interphase) and M phase ( mitotic phase) is called
the cell cycle.
Interphase is called „resting stage”, but it is in fact a period of great activity. Three
important process, which are preparatory to cell division, take place during interphase.
Thus it is also known as preparatory phase. These processes are
- Replication of DNA along with the synthesis of nuclear proteins such as the
histones
- In animal cells, duplication of centriole takes place by the outgrowth of daughter
centrioles from the parent centrioles, which are at right angle to each other.
- Synthesis of embryo rich compounds, which provide energy for mitosis, and
synthesis of proteins at the end of interphase states or periods, a long non -dividing
growth I-phase and a short dividing M-phase. Both have substages. I-phase represents
interphase.
The regular sequence of G1, S, G2 ( interphase) and M phase ( mitotic phase) is called
the cell cycle.
Interphase is called „resting stage”, but it is in fact a period of great activity. Three
important process, which are preparatory to cell division, take place during interphase.
Thus it is also known as preparatory phase. These processes are
- Replication of DNA along with the synthesis of nuclear proteins such as the
histones
- In animal cells, duplication of centriole takes place by the outgrowth of daughter
centrioles from the parent centrioles, which are at right angle to each other.
- Synthesis of embryo rich compounds, which provide energy for mitosis, and
synthesis of proteins at the end of interphase
Interphase ( L.inter-in between, Gk-phase-stage) is intermitotic stage of cell division in
which a series of changes occur in newly formed cell and nucleus undergoes certain
, changes to be fit for division. Non dividing state of mature cell or nucleus is called
interphase. It is also called energy phase.
Interphase of dividing cell has been classified into three subphases -G1- Phase, S-phase
and G2-phase
G1-phase
G1 phase is also known as first growth phase or post mitotic gap phase. It is the longest
phase of cell division. In this phase different types of RNA (mRNA, tRNA, rRNA) and
proteins are synthesized.
All cell organelles ( ER, mitochondria, Golgi complex, ribosomes, plasmid in plant cell)
multiply. The duration of G1 Phase varies from cell to cell. It is shorter in frequently
dividing cells. G1 phase cell has three options.
a) Continuous cycle and enter S phase
b) Stops cell cycle and enter quiescent phase or g0 phase
c) Stops cell cycle and undergoes cell differentiation
The deciding factor for above option are availability of mitogen and energy rich
compounds. This point is called check point .
S-phase
S-phase is known as synthetic phase. In this stage replication of DNA takes place by the
synthesis of histones. As a result each chromosome under goes replication producing two
chromatids. Each chromosome carries a duplicate set of genes. A haploid cell (n)
, becomes diploid (2n) and a diploid cell (2n), thus becomes tetraploid (4n) at the end of S-
phase. Repairing of damaged DNA also takes place.
G2-phase
G2 is also called second growth phase or pre-mitotic gap phase. In this phase synthesis of
DNA stops and synthesis of RNAs and proteins continues. All cell organelles multiply
and spindle formation takes place. It lasts for 2-5 hours in most cells. Some proteins
formed in this phase cause condensation of chromosomes to initiate mitosis
G0-phase
The phase in which cells fail to divide further ( do not undergo S-phase after G1-phase)
and undergo differentiation is known as G0 phase or quiescent stage. It occurs due to
non-availability of mitogen and energy rich compounds. The cells remain metabolically
active, grow in size and differentiate for particular function after attaining a particular
shape.
However some cells remain in undifferentiated state as reserve cells. They may proceed
with cell division when required e.g. fibroblasts; it helps in healing of wounds and grow
and divide again.
M-phase
The process of cell division is found to be essentially the same in all living organism and
the events are chiefly centered in the nucleus. Three type of cell divisions have been
distinguished:
- Amitosis or direct cell division
- Mitosis or indirect cell division
- Meiosis or reduction division
Mitosis and meiosis are the two major types of cell division. The basic stage in both the
types of divisions are almost identical.
Amitosis is a direct division characterized by the splitting of nucleus followed by that of
cytoplasm.
Mitosis is a somatic cell division which takes place in vegetative cells. It maintains the
chromosome number.
Meiosis is a reduction division, occurring in the reproductive cells. The chromosome
number are reduced to half.
