, The cell cycle
The cell cycle is the process that all body
cells in multicellular organisms use to grow
& divide.
It starts when a cell has been produced by
cell division and ends with the cell dividing
to produce 2 identical cells.
As the molecular events that control the
cell cycle happen in a specific sequence
they can ensure that the cycle cannot be
reversed and the DNA is only duplicated
once during each cell cycle.
, Interphase
The interphase is the longest phase of the cycle. It appears uneventful under a
microscope but during interphase elaborate preparations are being made for cell
division, in a carefully ordered and controlled sequence with checkpoints:
G0 (gap 0) phase- a resting phase triggered during early G1at the restriction
point by a checkpoint chemical. Some cells such as epithelial cells which line the
gut do not have this phase. In this phase, cells may undergo apoptosis (programmed
cell death), differentiation or senescence (cell stops dividing). Some types of cells
such as neurons remain in this phase for a very long time or forever.
G1 (gap 1) phase (growth phase)- cells grow & increase in size, organelles
duplicate, synthesis of enzymes needed for DNA replication & transcription of
genes to make RNA.
S (synthesis) phase- once the cell has entered this phase it is committed to
completing the cell cycle. In this phase DNA replication occurs - there is a specific
sequence of replication of genes; housekeeping genes (genes active in all types of
cells) are duplicated first and genes that are normally inactive in specific types of
cells are replicated last. When all chromosomes have been duplicated each one
forms sister chromatids. This phase is rapid as the exposed DNA pairs are more
susceptible to mutagenic agents, this reduces the chance of spontaneous mutations
happening,
G2 (gap 2) phase- special chemicals ensure that the cell is ready for mitosis by
stimulating proteins that will be involved in making chromosomes condense and in
the formation of the spindle. In this stage the cell grows and specific proteins are
stimulated.
The cell cycle is the process that all body
cells in multicellular organisms use to grow
& divide.
It starts when a cell has been produced by
cell division and ends with the cell dividing
to produce 2 identical cells.
As the molecular events that control the
cell cycle happen in a specific sequence
they can ensure that the cycle cannot be
reversed and the DNA is only duplicated
once during each cell cycle.
, Interphase
The interphase is the longest phase of the cycle. It appears uneventful under a
microscope but during interphase elaborate preparations are being made for cell
division, in a carefully ordered and controlled sequence with checkpoints:
G0 (gap 0) phase- a resting phase triggered during early G1at the restriction
point by a checkpoint chemical. Some cells such as epithelial cells which line the
gut do not have this phase. In this phase, cells may undergo apoptosis (programmed
cell death), differentiation or senescence (cell stops dividing). Some types of cells
such as neurons remain in this phase for a very long time or forever.
G1 (gap 1) phase (growth phase)- cells grow & increase in size, organelles
duplicate, synthesis of enzymes needed for DNA replication & transcription of
genes to make RNA.
S (synthesis) phase- once the cell has entered this phase it is committed to
completing the cell cycle. In this phase DNA replication occurs - there is a specific
sequence of replication of genes; housekeeping genes (genes active in all types of
cells) are duplicated first and genes that are normally inactive in specific types of
cells are replicated last. When all chromosomes have been duplicated each one
forms sister chromatids. This phase is rapid as the exposed DNA pairs are more
susceptible to mutagenic agents, this reduces the chance of spontaneous mutations
happening,
G2 (gap 2) phase- special chemicals ensure that the cell is ready for mitosis by
stimulating proteins that will be involved in making chromosomes condense and in
the formation of the spindle. In this stage the cell grows and specific proteins are
stimulated.
