Cellular Signaling I Flashcards
first messenger
Signaling involves a signaling molecule released on one part of the body that travels to a protein receptor found in the membrane of target cells in another part of the body. The protein receptor’s shape is changed as a result of binding of the first messenger and that causes changes internal to the cell that results in a cellular response.
cellular response
usually results in changes of gene expression (transcription) or changes in enzyme activity affecting metabolism.
The lipid bilayer
a barrier to entry of most molecules. Notable exceptions are steroid hormones which have roles in signaling. They enter cells directly and interact with receptors located inside of the target cells.
gated ion channels
The simplest signaling system involve gated ion channels that open or close in response to binding of an effector. This can result in movement of materials, such as ions into or out of cells and result in voltage changes across membranes. This can play a role in transmission of nerve signals.
Hormones
compounds made in one part of the body that travel in the bloodstream to target cells in another part of the body where they bind to receptors and elicit responses. Hormones include steroid molecules, amino acid derivatives, and peptides.
non-steroid hormone signaling
receptors are located on the surface of the cell. Often they stimulate production of second messenger molecules in the cell after binding to a hormone. Second messengers include cAMP, cGMP, calcium, IP3, and diacylglycerol.
Signaling systems involving steroid hormones
tend to be simpler than signaling system for other hormones.
7TM receptors
a class of receptors that are involved in a variety of bodily functions. The beta-adrenergic receptor is a 7TM. 7TM refers to the fact that the protein crosses the cell membrane 7 times.
G-protein.
7TM receptors have a protein partner on the inside of the cell that helps them to transmit the signal. This partner is known as a G-protein.
G-proteins binding
can bind guanine nucleotides - GTP or GDP. G-proteins interact with the carboxy tail of the beta-adrenergic receptor. G-proteins have three subunts - alpha, beta, and gamma. When there is no signal present, alpha has GDP bound to it.
(G-protein) Binding of the beta-adrenergic receptor of a signal (epinephrine here)
causes the G-protein to change in response. This causes the alpha subunit to bind GTP and lose GDP. GTP is SWAPPED for the GDP.
When the alpha subunit has GTP bound
it separates from the beta and gamma subunits and moves to a membrane-bound enzyme known as adenylate cyclase. This enzyme catalyzes the conversion of ATP to cAMP. Thus, a second messenger has been created. cAMP can move in the cytoplasm and interact with and activate protein kinase A.
