logo

Animation: Signal Transduction Pathways

by Pearson
4 views
Was this helpful ?
0
Receptors that are plasma membrane proteins usually affect the cell through multistep signal transduction pathways. These pathways allow for amplification of signals and signal coordination and regulation. Signal transduction often involves small molecules called second messengers and protein phosphorylation by enzymes called protein kinases. Second messengers are small nonprotein molecules that act as intermediaries in signal transmission. Two important second messengers are cyclic AMP, abbreviated cAMP, and calcium ions. Both of these second messengers participate in pathways initiated by both G protein-coupled receptors and receptor tyrosine kinases, but we're showing only one example for each second messenger. Let’s see how cyclic AMP acts as a second messenger in signal transduction. In this example, epinephrine, a water-soluble hormone, acts as the first messenger. An epinephrine molecule docks with a G protein-coupled receptor, which activates a G protein that activates the enzyme adenylyl cyclase. Adenylyl cyclase converts ATP into cyclic AMP, which quickly diffuses through the cell and acts as a second messenger, triggering further steps in the signaling pathway. In this example, cAMP is shown activating a protein kinase. Calcium ions also act as second messengers in signal transduction pathways. This time we will show a receptor tyrosine kinase, but G protein-coupled receptors can also initiate this pathway. The signaling molecule docks with the receptor, which activates an enzyme called phospholipase C. This activated enzyme cleaves a small molecule called inositol trisphosphate, abbreviated IP3, from a certain kind of membrane phospholipid. IP3 docks with an IP3-gated calcium channel in the membrane of the endoplasmic reticulum. The channel opens, releasing calcium ions into the cytoplasm, where they activate enzymes that carry out a cellular response. Now let's look at the role of protein kinases in a signal transduction pathway. A signaling molecule binds to a receptor and initiates a signal transduction pathway. In this example, cyclic AMP is generated and activates the first protein kinase. A protein kinase catalyzes the transfer of phosphate groups from ATP to another protein. The protein that gets activated is usually also a protein kinase, which may act on still another protein kinase. One kinase may activate many molecules of the next kinase in the chain, thus amplifying the signal. The last kinase then activates many molecules of the protein that carries out the final cellular response.
Receptors that are plasma membrane proteins usually affect the cell through multistep signal transduction pathways. These pathways allow for amplification of signals and signal coordination and regulation. Signal transduction often involves small molecules called second messengers and protein phosphorylation by enzymes called protein kinases. Second messengers are small nonprotein molecules that act as intermediaries in signal transmission. Two important second messengers are cyclic AMP, abbreviated cAMP, and calcium ions. Both of these second messengers participate in pathways initiated by both G protein-coupled receptors and receptor tyrosine kinases, but we're showing only one example for each second messenger. Let’s see how cyclic AMP acts as a second messenger in signal transduction. In this example, epinephrine, a water-soluble hormone, acts as the first messenger. An epinephrine molecule docks with a G protein-coupled receptor, which activates a G protein that activates the enzyme adenylyl cyclase. Adenylyl cyclase converts ATP into cyclic AMP, which quickly diffuses through the cell and acts as a second messenger, triggering further steps in the signaling pathway. In this example, cAMP is shown activating a protein kinase. Calcium ions also act as second messengers in signal transduction pathways. This time we will show a receptor tyrosine kinase, but G protein-coupled receptors can also initiate this pathway. The signaling molecule docks with the receptor, which activates an enzyme called phospholipase C. This activated enzyme cleaves a small molecule called inositol trisphosphate, abbreviated IP3, from a certain kind of membrane phospholipid. IP3 docks with an IP3-gated calcium channel in the membrane of the endoplasmic reticulum. The channel opens, releasing calcium ions into the cytoplasm, where they activate enzymes that carry out a cellular response. Now let's look at the role of protein kinases in a signal transduction pathway. A signaling molecule binds to a receptor and initiates a signal transduction pathway. In this example, cyclic AMP is generated and activates the first protein kinase. A protein kinase catalyzes the transfer of phosphate groups from ATP to another protein. The protein that gets activated is usually also a protein kinase, which may act on still another protein kinase. One kinase may activate many molecules of the next kinase in the chain, thus amplifying the signal. The last kinase then activates many molecules of the protein that carries out the final cellular response.