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Cell Communication AP Biology Communication Methods Cell-to-cell contact Local signaling Long distance signaling AP Biology Cell-to-Cell Communications Cell junctions directly connect the cytoplasm of adjacent cells Ex: cardiac cells for rhythmicity; plamodesmata between plant cells Surface receptors can give/send information Ex: specific immune response Plasma membranes Gap junctions between animal cells AP Biology Plasmodesmata between plant cells VIDEO Local Signaling VIDEO Adjacent cells are signaled. Chemical messengers released Ex: Neurotransmitters via neurons Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Secretory vesicle Local regulator diffuses through extracellular fluid (a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid. AP Biology Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell. Yeast Sexual Reproduction 1 Yeast cells identify their mates by cell signaling. 2 3 AP Biology Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type. Mating. Binding of the factors to receptors induces changes in the cells that lead to their fusion. New a/ cell. The nucleus of the fused cell includes all the genes from the a and a cells. factor Receptor a Yeast cell, mating type a factor Yeast cell, mating type a a/ Long Distance Signaling Use of hormones Both plants and animals use hormones (e.g. Insulin) Can affect many cells in Other parts of the body Long-distance signaling Endocrine cell Protein or Steroid types Blood vessel Hormone travels in bloodstream to target cells Target cell AP Biology Figure 11.4 (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all C body cells. How Does it Work? Signal Transduction Pathways Convert signals on a cell’s surface into cellular responses Are similar in microbes and mammals, suggesting an early origin AP Biology 3 Phases of Signal Transduction EXTRACELLULAR FLUID 1 Reception Plasma membrane CYTOPLASM 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Figure 11.5 AP Biology Step One - Reception Reception occurs when a signal molecule (ligand) binds to a receptor protein. Ligand and receptor have a unique bonding AP Biology Step Two - Transduction Signal initiated by conformational change of receptor protein Signal is turned into a cellular response. Signaling cascades relay signals to target Multistep pathways can amplify a signal AP Biology Second messengers involved Step Three - Response Cell signaling leads to regulation of cytoplasmic activities or transcription Signaling pathways regulate a variety of cellular activities AP Biology A phosphorylation cascade Signal molecule Receptor Activated relay molecule Inactive protein kinase 1 2 Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase. Active protein kinase 1 Inactive protein kinase 2 ATP PP Inactive protein kinase 3 5 Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse. Figure 11.8 P Active protein kinase 2 ADP Pi AP Biology 1 A relay molecule activates protein kinase 1. 3 Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3. ATP ADP Pi Active protein kinase 3 PP Inactive protein P 4 Finally, active protein kinase 3 phosphorylates a protein (pink) that brings about the cell’s response to the signal. ATP ADP Pi PP P Active protein Cellular response Benefits of a 2° messenger system signal 1 Activated adenylyl cyclase receptor protein 2 Not yet activated amplification 4 3 GTP amplification cAMP amplification 5 G protein protein kinase 6 amplification Amplification! enzyme Cascade multiplier! AP Biologyresponse! FAST 7 amplification VIDEO product Cyclic AMP example… First messenger (signal molecule such as epinephrine) Adenylyl cyclase G protein G-protein-linked receptor GTP ATP cAMP Protein kinase A Cellular responses AP Biology Pathways can also regulate genes by activating transcription factors that turn genes on or off Growth factor Receptor Phosphorylation cascade Reception Transduction CYTOPLASM Inactive transcription Active transcription factor factor P Response Figure 11.14 DNA Gene AP Biology NUCLEUS mRNA Types of Receptors There are three main types of plasma membrane receptors: G-protein-linked Tyrosine kinases Ion channel AP Biology G-protein-linked receptors Very common Results in a single pathway response G-protein-linked Receptor Plasma Membrane GDP CYTOPLASM G-protein (inactive) Enzyme Activated Receptor GDP Signal molecule GTP Activated enzyme GTP GDP Pi Cellular response AP Biology Inactivate enzyme 1 A signal molecule binds 2 Phospholipase C cleaves a to a receptor, leading to activation of phospholipase C. plasma membrane phospholipid called PIP2 into DAG and IP3. EXTRACELLULAR FLUID 3 DAG functions as a second messenger in other pathways. Signal molecule (first messenger) G protein DAG Ex: Inositol P3 and calcium GTP PIP2 G-protein-linked receptor Phospholipase C IP3 (second messenger) IP3-gated calcium channel Endoplasmic reticulum (ER) Various proteins activated Ca2+ Cellular response Ca2+ (second messenger) 4 IP3 quickly diffuses through AP Biology the cytosol and binds to an IP3– gated calcium channel in the ER membrane, causing it to open. 5 Calcium ions flow out of 6 The calcium ions the ER (down their concentration gradient), raising the Ca2+ level in the cytosol. activate the next protein in one or more signaling pathways. Receptor tyrosine kinases Multiple pathway response Signal-binding site Signal molecule Helix in the Membrane Signal molecule Tyrosines Tyr Tyr Tyr CYTOPLASM Receptor tyrosine kinase proteins (inactive monomers) Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Dimer Figure 11.7 Activated relay proteins Tyr Tyr Tyr Tyr Tyr Tyr 6 ATP Activated tyrosinekinase regions (unphosphorylated dimer) AP Biology 6 ADP P Tyr P Tyr P Tyr Tyr P Tyr P Tyr P Fully activated receptor tyrosine-kinase (phosphorylated dimer) P Tyr P Tyr P Tyr Tyr P Tyr P Tyr P Inactive relay proteins Cellular response 1 Cellular response 2 Ion channel receptors When ligand binds, channel can open or close. Ex: neurotransmitters bind as ligands for Na+ ion channels Signal molecule (ligand) Gate closed Ligand-gated ion channel receptor Ions Plasma Membrane Gate open Cellular response Gate close AP Biology Figure 11.7 *Intracellular Receptors Target protein is INSIDE the cell Must be hydrophobic molecule Hormone EXTRACELLULAR (testosterone) FLUID Why can the signal molecule meet its target INSIDE the cell? Receptor protein Plasma membrane Hormonereceptor complex 2 Testosterone binds to a receptor protein in the cytoplasm, activating it. NUCLEUS CYTOPLASM receptor complex enters the nucleus and binds to specific genes. 4 mRNA AP Biology hormone testosterone passes through the plasma membrane. 3 The hormone- DNA Figure 11.6 1 The steroid New protein The bound protein stimulates the transcription of the gene into mRNA. 5 The mRNA is translated into a specific protein. Evolutionary Significance Unicellular and multicellular cell communication have similarities Yeast cells signal for sexual reproduction through signal transduction process. Bacteria secrete molecules to sense density of own population. Quorum Sensing (survival purpose) TEDED on Quorum Sensing AP Biology