sheet no.16

Cell Cycle

Consists of 2 major events:

a) Interphase.
b) Mitosis.

- Interphase is longer than Mitosis.

- In the Interphase the cell grows and duplicates its organelles and genetic material.
The Interphase stage consists of:
1) G1 phase: this phase is the major period of cell growth during its lifespan.
2) S phase: (synthesis) is the phase in which the cell duplicates its DNA.
3) G2 phase: is the phase in which the cell undergoes a period of rapid growth to prepare for mitosis.
M = Mitosis Stage
I = Interphase stage
- G0 phase: Some cells (like muscle cells) don’t divide more after mitosis and they become in a resting stage. Peripheral lymphocytes are stimulated to re-enter the cell cycle and divide after exposure to radiation, wounds, or diseases.
- Some cells leave the cell cycle(rest) permanently (like muscle cells(myocytes) and nerve cells(neurons)) while others leave it(rest) temporarily (like peripheral lymphocytes).

-In case of bone fracture:
a) Periosteum: is a membrane that lines the outer surface of all bones and it contains osteoprogenitor cells which produce osteoblasts. Periosteum is stimulated to produce osteoblasts when the bone is fractured.
b) Osteoblast: is the matrix formation of cell. It produces osteocytes.
c) Osteocyte: are maintenance cells.
d) Osteoclast: remodeling cells to reshape the fractured bones.

- How Cells Divide:

1) Somatic Cells – by Mitosisàgive 2 identical daughter cells
2) Reproductive Cells – by Meiosisàgive 2 in identical cells