Topic 21 Cytophysiology– vital and mitotic cycle of the cell. Amitosis mitosis, meiosis

TOPIC 21 Cytophysiology– vital and mitotic cycle of the cell. Amitosis mitosis, meiosis

As the cell develops from a stem cell to a fully differentiated cell, it goes through two main phases where it actively divides (during mitosis) and where it is in an apparent resting phase, preparing itself for cell division (interphase).

Interphase

Interphase is the longest phase of the cell cycle. The cell spends majority of its time preparing itself for cell division/mitosis. It lasts about 12-24h in mammals and is essential to make the next mitosis possible. Interphase is subdivided into 4 steps:

1. 1. G1 – The cell grows in size and accumulates the enzymes, nucleotides, proteins and organelles such as mitochondria needed for DNA replication. G1 is the longest period in Interphase.

G1/S checkpoint – checks whether the cell nutrition, size, environment is favourable and whether the DNA is still intact.

1. 2. S (synthesis) – DNA replication occurs in this synthesis S phase.
2. 3. G2 – between synthesis and mitosis, the cell will continue to grow and produce new proteins in preparation for mitosis.

G2/M checkpoint – ensures that the DNA replication is complete.

1. 4. M (mitosis) – includes all the phases of mitosis itself.
2. 5. Gap 0 (G0) – is the phase of cell cycle arrest. Phase of differentiation. Differentiating cells in growing tissues may have a very long G1 period, these cells are said to be in the G0 phase of the cell cycle.