Mitotic Cell Cycle
Normal growth, development and maintenance of a cell depend on the timing and
rate of mitosis
Various cell types differ in their patter of cell division e.g.
- Human skin cells divide frequently
- Liver cells only divide in appropriate situations such as wound repair
- Nerve and muscle cells do not divide in mature humans
The cell cycle is a well-ordered sequence of events in which a cell duplicated its
contents and divides in two
The cell cycle alternates the mitotic (M-phase dividing phase) and Interphase
(non-dividing phase)
- M phase shortest phase in which cell divides and includes:
Mitosis division of the nucleus
Cytokinesis division of the cytoplasm
10% of the cell cycle
- Interphase includes most of the cell’s growth and metabolic activity
90% of cell cycle
Period of intense biochemical activity during which the cell grows and
copies its chromosomes in preparation for cell division
Consists of 3 periods: G1, S and G2 phase
Interphase
G1 phase (Gap 1)
* Normal metabolic activity
* Number of cell organelles increase to normal levels
* Volume of cytoplasm increases mature size
* Time spent in G1 will vary can remain indefinitely
* Growth and development if not enough the cell will remain in G1 until there
are enough nutrients to support the cell through the entire mitotic cell cycle
S phase (Synthesis)
* Inside the nucleus, the chromosomes (DNA) begin to duplicate
* Results in two identical copies of chromosomes called sister chromatids
* Sister chromatids attach to each other at the centromere
* Cell committed to cell division
G2 phase (Gap 2)
* Structures directly involved in mitosis are formed or replicated
* Centrioles in animal cells replicate to form two pairs
* New DNA is checked
* Substances needs for mitosis are synthesised
Regulation of the cell cycle
® Checkpoint = critical control point in the cell cycle where ‘stop’ and ‘go-ahead’
signals can regulate the cell cycle
® G1 checkpoint = restriction point
, * Ensures that the cell is large enough to divide and that enough nutrients are
available to support resulting daughter cells
* If a cell receives a ‘go-ahead’ signal, it will continue with the cell cycle; if not it
will exit the cell cycle and switch to a non-dividing state called GØ G zero
® G2 checkpoint
* Ensures that DNA replication in S phase has been completed successfully
® When cell population reaches a certain density the amount of growth factors and
nutrients available to each cell becomes insufficient to allow continued cell growth
® For most animal cells to divide they must be attached to a substratum (extracellular
matrix of a tissue) – anchorage is signalled via pathways involving membrane
proteins and the cytoskeleton
Cancer cells
® Do not respond normally to the bodies control mechanisms
® Divide excessively and invade other tissues
Normal growth, development and maintenance of a cell depend on the timing and
rate of mitosis
Various cell types differ in their patter of cell division e.g.
- Human skin cells divide frequently
- Liver cells only divide in appropriate situations such as wound repair
- Nerve and muscle cells do not divide in mature humans
The cell cycle is a well-ordered sequence of events in which a cell duplicated its
contents and divides in two
The cell cycle alternates the mitotic (M-phase dividing phase) and Interphase
(non-dividing phase)
- M phase shortest phase in which cell divides and includes:
Mitosis division of the nucleus
Cytokinesis division of the cytoplasm
10% of the cell cycle
- Interphase includes most of the cell’s growth and metabolic activity
90% of cell cycle
Period of intense biochemical activity during which the cell grows and
copies its chromosomes in preparation for cell division
Consists of 3 periods: G1, S and G2 phase
Interphase
G1 phase (Gap 1)
* Normal metabolic activity
* Number of cell organelles increase to normal levels
* Volume of cytoplasm increases mature size
* Time spent in G1 will vary can remain indefinitely
* Growth and development if not enough the cell will remain in G1 until there
are enough nutrients to support the cell through the entire mitotic cell cycle
S phase (Synthesis)
* Inside the nucleus, the chromosomes (DNA) begin to duplicate
* Results in two identical copies of chromosomes called sister chromatids
* Sister chromatids attach to each other at the centromere
* Cell committed to cell division
G2 phase (Gap 2)
* Structures directly involved in mitosis are formed or replicated
* Centrioles in animal cells replicate to form two pairs
* New DNA is checked
* Substances needs for mitosis are synthesised
Regulation of the cell cycle
® Checkpoint = critical control point in the cell cycle where ‘stop’ and ‘go-ahead’
signals can regulate the cell cycle
® G1 checkpoint = restriction point
, * Ensures that the cell is large enough to divide and that enough nutrients are
available to support resulting daughter cells
* If a cell receives a ‘go-ahead’ signal, it will continue with the cell cycle; if not it
will exit the cell cycle and switch to a non-dividing state called GØ G zero
® G2 checkpoint
* Ensures that DNA replication in S phase has been completed successfully
® When cell population reaches a certain density the amount of growth factors and
nutrients available to each cell becomes insufficient to allow continued cell growth
® For most animal cells to divide they must be attached to a substratum (extracellular
matrix of a tissue) – anchorage is signalled via pathways involving membrane
proteins and the cytoskeleton
Cancer cells
® Do not respond normally to the bodies control mechanisms
® Divide excessively and invade other tissues
