Transcript G proteins
Cell Communication Keri Muma Bio 6 Types of Cellular Communication Direct contact between cells Gap junctions – cells are connected by tunnels formed by connexons Allows ions and small water soluble chemicals to pass between cells Cardiac and smooth muscle Types of Cellular Communication Direct contact between cells Cell to cell recognition – interaction of cellsurface molecules Immune cells – recognize self vs. non-self Types of Cell Communication Through extracellular chemical messengers Cells release ligands that bind to receptors on target cells to initiate a desired cellular response Types of Cell Communication Local Regulators Paracrine – through diffusion, ligands affect cells in the local vicinity Autocrine – chemicals act on the cell that produced it Examples: histamine, cytokines, prostaglandins Local Regulators Neurotransmitters – secreted by neurons Diffuse across the synaptic cleft and target the adjacent cell (neuron, gland, muscle) Short-lived Types of Cellular Communication Long-range (distant) regulators Hormones – secreted into the blood by endocrine glands to travel to distant target cells Neurohormones – neurons secretes hormones into the blood Cellular Effects of Chemical Signals Example of various effects chemical signals may have on the target cell Activate or inhibit enzymes Direct protein synthesis through activation of transcription factors Stimulate cell division Alter membrane permeability – membrane potential or opening/closing of ion channels How do hormones work? Hormones are chemical substances that travel through the blood to a target cell Target cells must have specific receptors to which the hormone binds These receptors may be intracellular or located on the plasma membrane They trigger a change in cellular activity Types of Hormones Amines – amino acid derivatives Peptides – proteins Vasopressin, insulin Steroids – cholesterol based Catecholamines (NE and E), T3, T4, serotonin, melatonin Cortisol, aldosterone, estrogen, testosterone Eicosanoids –derived from arachidonic acid Prostaglandins, leukotrienes Transport of Hormones Hydrophilic (water-soluble) hormones – transported dissolved in the plasma Peptide and catecholamines Lipophilic (lipid-soluble) hormones – circulate bound to plasma proteins such as albumin Steroids and thyroid hormones Mechanism of Signaling Molecules Lipid soluble hormones Move through the plasma membrane and bind to an intracellular receptor in the nucleus Binding of the HRC to the DNA triggers transcription of a specific gene and the synthesis of a protein that initiates a cellular response Mechanisms of Signaling Molecules Water soluble hormonesutilize a membrane bound receptor Binding of hormone causes a conformational change in the receptor Two affects of ligands binding to membrane bound receptors: 1.Triggers the opening or closing of ion channels Mechanisms of Signaling Molecules OR 2.Transfers the signal to a secondary messenger within the cell which triggers a cascade of biochemical events Types of Receptors Signal Transduction Secondary Messenger Pathways G-protein linked receptor – spans the membrane and is associated with a G protein on the cytoplasmic side Ligand binds to the receptor Receptor then activates a G protein G proteins are considered relay proteins that cycle between an inactive and active form Cyclic AMP Secondary Messenger Pathway 1. 2. 3. 4. G protein activates the enzyme adenylate cyclase (the effector) Converts ATP to cyclic AMP Activates protein kinase A which phosphorylates other proteins Trigger cellular responses Cyclic AMP Secondary Messenger Pathway Signaling Pathways Amplify the Cells Response to Signals Molecules in second messenger system Total number of molecules Extracellular chemical messenger bound to membrane receptor Activated adenylyl cyclase 1 Amplification (10) 10 Amplification Cyclic AMP (100) Activated protein kinase Phosphorylated (activated) protein (e.g., an enzyme) Products of activated enzyme 1,000 1,000 Amplification (100) 100,000 Amplification (100) 10,000,000 Calcium Secondary Messenger Pathway 1. Binding of extracellular messenger to a G protein linked receptor or a tyrosine kinase receptor 2. Activates phospholipase C which converts PIP2 to DAG and IP3 Calcium Secondary Messenger Pathway 3. DAG will activate protein kinase C in another signaling pathway 4. IP3 binds to calcium channels triggering the release of calcium from the ER into the cytoplasm Calcium Secondary Messenger Pathway 5. Calcium binds to and activates calmodulin which can alter other proteins to bring about a cellular response Calcium Secondary Messenger Pathway Calcium Secondary Messenger Pathway Summary of Signaling Pathways