The Problem Of Cell Growth
As cells grow they hit two limits: DNA and exchange limits. As a cell grows, the DNA cannot produce enough to maintain the cell. Also, as a cell grows, its volume increases faster than its surface area, meaning that it cannot keep up material exchange to the size of the cell. Thus, to solve these growth problems, the cell divides.
Cell communication - Paracrine signal vs. Endocrine signal
Cell signals can be local signal (paracrine signal) which is communicated through cell-cell contacts, or endocrine signal which is mostly hormones secreted by glands and transported via blood.
Proliferating cells undergo cell cycle which is composed of G1, S, G2 and M phases. Resting cells are in G0. Cell cycle is controlled by cyclins and CDKs, when circumstances are not right, cell cycle checkpoints can be activated to restrain cell cycle.
Mitosis is cell division, with an exact replication of the cell’s DNA into a new clone cell. Mitosis has four stages: prophase, metaphase, anaphase, and telophase. All of these steps lead to separation of the duplicated DNA in order to give them to the new cell. After mitosis, cytokinesis splits the cell membranes and cytoplasm into two new identical cells.
Cell Cycle Control
There are 4 major cell cycle checkpoints: G1 checkpoint, intra-S phase checkpoints, G2 checkpoints and spindle checkpoints. These are regulated by cyclins and kinases. When cell cycle checkpoints are broken or cell cycle goes wrong, cells may undergo apoptosis or become cancerous.