What is cancer?
Cancer is a disease characterized by uncontrolled division of cells in the body. It is usually caused by DNA mutations in the cell's nucleus. These mutations affect signal transduction pathways related to the cell cycle (cell division). Examples of this would be amplifying/over-expressing a gene, over-activating a growth factor, deactivating tumor-suppressor genes, or synthesizing a protein with the wrong structure, which can alter or inhibit its function.
Signal Transduction Pathways
G-Protein
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Here are some of the most common signal transduction pathways. This is a G-protein transduction pathway. In this pathway, a signal molecule outside of the cell, called a ligand, binds to the active site of a G-protein-linked receptor and the receptor undergoes a conformational change. The G-protein then binds to the receptor and switches out GDP for GTP. It then phosphorylates an enzyme, adenylyl cyclase, which activates a phosphorylation cascade (see next image).
Phosphorylation Cascade
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The phosphorylation cascade is so called because it activates two types of enzymes: 1) kinases transfer phosphate groups, which hold a great amount of energy and activate most molecules; and 2) phosphatases remove phosphate groups, usually to deactivate molecules.
A phosphorylation cascade is the process that ultimately evokes the cellular response.
A phosphorylation cascade is the process that ultimately evokes the cellular response.
Tyrosine Kinase
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Tyrosine kinase receptors work similarly to G-proteins. However, they are made up of two different parts that dimerize (join) when a ligand binds to them. Once this occurs, the tyrosines, amino acids, attached to the receptors are phosphorylated with ATP (energy packets). Relay molecules attach to the tyrosine and in turn are activated. This activates the phosphorylation cascade.