Problem 8

Background and context

Peptide hormones cannot cross the plasma membranes of cells directly. They need surface receptors located on the surface of the plasma membrane to stimulate a signaling pathway which in turn stimulates an intracellular activity. These hormones bind to surface receptors and are called first messengers. This starts the signaling pathway and G-proteins are activated.  G-proteins stimulate a second messenger called cyclic AMP or cAMP in the cytoplasm. Cyclic AMP or cAMP activates protein kinases which add phosphate groups from ATP molecules to substrate molecules. This activates the substrate molecules triggering cellular activities.