Cell Communication and Cell Signaling
Why is cell signaling important?
Why is cell signaling important? Allows cells to communicate and coordinate functions/activities of the organism Usually involves the cell membrane
Cell Communication Communication involves transduction of stimulatory or inhibitory signals from other cells, organisms or the environment Correct and appropriate signal transduction pathways are generally under strong selective pressure
Single-Celled Organisms Signal transduction pathways influence how the cell responds to its environment Example: quorum sensing in bacteria
Multicellular Organisms Signal transduction pathways coordinate the activities within individual cells that support the function of the organism as a whole Example: Epinephrine stimulation of glycogen breakdown in mammals
Cell Communication Local Signaling Cell Junctions Cell to Cell Contact Local Regulators Long Distance Signaling Hormones Neural Circuits
Local Signaling: Cell Junctions Plasmodesmata in plant cells and gap junctions in animals Allows signaling molecules to pass readily between adjacent cells
Local Signaling: Cell-to-Cell Contact Communication through direct interaction between molecules extending from the surface of the cells (glycolipids and glycoproteins) Example: tissue development and immune responses
Local Signaling: Local Regulators Local regulators are signaling molecules that only target cells in the vicinity of the emitting cell Examples: paracrine signaling and synaptic signaling
Evolution: Paracrine Signaling Paracrine factors involved in differential development are similar between different species Evidence of common ancestry, highly conserved in animals from fruit flies to humans Receptor and Pathway Groups: - Fibroblast Growth Factor Family (blood vessel, wound healing, limb development, embryonic development) - Hedgehog Family (embryonic development, bilateralism) - Wnt Family (bone, heart, muscle, regeneration of tissue) - TGF β Family (immunity, cell proliferation)
Long Distance Signaling: Hormones Endocrine signals (hormones) produced by endocrine cells travel long distances through the blood to reach all parts of the body Example: Insulin produced in pancreas, targets liver cells
Plants Have Hormones! Ethylene gaseous hormone that ripens fruit Auxin chemical messenger that influences fruit development and cell growth
Long Distance Signaling: Neural Circuits Neurons may transmit messages (nerve impulses) over a long distance
Local or Long Distance - Cell Signaling Pathway is Similar Reception Transduction Response
Cell Signaling Pathway
Stage 1: Signal Reception Signaling begins with the recognition of a chemical messenger (ligand) by a receptor protein Complementary shapes
Types of Receptor Proteins Transmembrane Proteins (within the cell membrane) - G Protein-Coupled Receptors (GPCRs) - Ligand-Gated Ion Channels Intracellular Receptors (within cytoplasm or nucleus) - Targeted by lipid soluble ligands (pass through the plasma membrane)
Transmembrane Protein Receptors: GPCRs
Transmembrane Protein Receptors: Ligand-Gated Ion Channels
Intracellular Receptors
Receptor Proteins Different receptors recognize different chemical messengers, which can be peptides, small chemicals, or proteins, in a specific oneto-one relationship A receptor protein recognizes signal molecules, causing the receptor protein s shape to change, which then initiates transduction of the signal
Review of Signal Reception What occurs during Stage 1: Signal Reception? What is a ligand? What is the difference between transmembrane protein receptors and intracellular receptors?
Stage 2: Signal Transduction Signal transduction is the process by which a signal is converted to a cellular response One step or a series of many steps
Signal Transduction Signaling cascades relay signals from receptors to cell targets, often amplifying the incoming signals Second messengers are often essential to the function of the cascade cyclic AMP (camp) or calcium ions (Ca 2+ )
Signaling Cascade Protein kinases turn on or activate proteins by adding phosphates to the proteins (phosphorylation cascade) Protein phosphatases turn off or deactivate proteins and kinases by removing phosphates from the proteins (dephosphorylation)
Second Messengers
Review of Signal Transduction What occurs during Stage 2: Signal Transduction? What is the function of a protein kinase? What is the function of a protein phosphatase? Identify a second messenger.
Stage 3: Cellular Response The signal transduction pathway initiates a change in cellular activity Response occurs in the cytoplasm or nucleus
Response: Regulation of Protein Synthesis Most signaling pathways activate transcription factors Transcription factors regulate cellular responses by: - Turning a gene on Protein OR - Turning a gene off No protein OR - Regulating the activity of a particular protein
Testosterone Cellular response increases gene activity for proteins involved in: Muscle mass Bone growth Body hair Reproductive tissue
Blood Glucose Regulation
Cell Signaling Summary