CELL CYCLE (INTERPHASE & MITOSIS)
INTERPHASE
• It takes approximately 80% of the cell's lifetime.
• Complete organelles
• Considered to be “resting" from cell division.
• The duration of a cell's life cycle varies from one
organism to another.
Examples:
Fly embryo - 8 minutes
mammals - 24 hours
• ln higher order species, the length of cell cycle is
usually controlled by how long it takes to replace
damaged cells.
G1 phase
• This stage involves preparation for synthesis and
replication of the cellular machinery.
• It is also in this stage where the cell monitors both
the internal and external environments t ensure that all
preparations for DNA synthesis have been completed
and overall conditions for cell division.
• G1 takes up about 41% of the cell's life cycle.
• The cell carries out all its normal activities and
accommodates all growth processes.
• G1 completed in about 10 hours
G1 checkpoints
• The cell checked if it is large and healthy enough to
continue through the next phases towards cell division.
• If fails, the cell will quit the cycle and remain in G0
• The proteins that activates that checkpoints in
interphase is kinase.
S Phase
• The cellular content of the DNA is duplicated in
this stage of the cell cycle.
• The length of S phase varies according to the total
DNA that the particular cell contains: the rate of
synthesis of DNA is fairly constant between cells
and species.
• Cell will take between 5 and 6 hours to complete
S phase.
• Taking up approximately 20% of the cell cycle.
• s phase in six hours
G2 Phase
• During this stage, the cell synthesizes the proteins
required to assemble the machinery required for the
separation of duplicated chromosomes (mitotic
process).
• G1 stage, the cells in G2 also monitor the internal
and external environments to ensure that faithful
replication of the DNA has occurred and that the
conditions for cytokines is favorable.
• There is a major check point at the end of G2
phase that controls the entry to M-phase
• G2 is shorter, lasting only 4 hours in most cells.
The stages of the cell cycle from G1, S and G2, are
preliminary stages before the actual cell division.
These preliminary stages are referred to as the
interphase or resting stage while the actual cell
division is the M phase.
MITOSIS
• This takes up 20% of the cell' life span
• All regular activities of the cells come to a stop
when it starts dividing.
M Phase
• This phase is characterized by an ordered series of
events that leads to the alignment and separation for
the duplicated chromosomes during the S phase of
the cell cycle.
Mitosis
