1.4c Hydrophilic signals and transduction NEED TO GO OVER Flashcards
Hydrophilic signalling molecules
They bind to transmembrane receptors and do not enter the cytosol. Peptide hormones and neurotransmitters are examples of hydrophilic extracellular signalling molecules.
What happens when a ligand binds to a transmembrane receptor?
Transmembrane receptors change conformation when the ligand binds to the extracellular face; the signal molecule does not enter the cell, but the signal is transduced across the plasma membrane.
What are signal transducers?
Transmembrane receptors act as signal transducers by converting the extracellular ligand-binding event into intracellular signals, which alters the behaviour of the cell.
Transduced hydrophilic signals often involve G-proteins or cascades of phosphorylation by kinase enzymes.
What do G-proteins do?
G-proteins relay signals from activated receptors (receptors that have bound a signalling molecule) to target proteins such as enzymes and ion channels.
Phosphorylation cascade
Phosphorylation cascades allow more than one intracellular signalling pathway to be activated. They involve a series of events with one kinase activating the next in the sequence and so on. Phosphorylation cascades can result in the phosphorylation of many proteins as a result of the original signalling event.
Insulin
Binding of peptide hormone insulin to its receptor causes a conformational change that triggers phosphorylation of the receptor. This start a phosphorylation cascade inside the cell, which eventually leads to GLUT4 - containing vesicles being transported to the cell membrane.
Diabetes
Diabetes mellitus can be caused by failure to produce insulin (type 1) or loss of receptor function (type 2)
Type 2 diabetes
Type 2 is generally associated with obesity. Exercise also triggers recruitment of GLUT4, so can improve uptake of glucose to fat and muscles cells in subjects with type 2.
