* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download BIO508- Topic 8 Lecture Notes File
Survey
Document related concepts
Cell culture wikipedia , lookup
Cell encapsulation wikipedia , lookup
Cell growth wikipedia , lookup
NMDA receptor wikipedia , lookup
Extracellular matrix wikipedia , lookup
Cell membrane wikipedia , lookup
Hedgehog signaling pathway wikipedia , lookup
Purinergic signalling wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Endomembrane system wikipedia , lookup
Cellular differentiation wikipedia , lookup
Cytokinesis wikipedia , lookup
G protein–coupled receptor wikipedia , lookup
Biochemical cascade wikipedia , lookup
List of types of proteins wikipedia , lookup
Transcript
SoS, Dept. of Biology, Lautoka Campus BIO508 Cell Slide Design: Copyright © McGraw-Hill Global Education Holdings, LLC. Biology Lecturer: Dr.Ramesh Subramani Topic 8: Cell Communication 1 How does cell signaling trigger the desperate flight of this gazelle? Cellular Messaging • Cell-to-cell communication is essential for both multicellular and unicellular organisms • Biologists have discovered some universal mechanisms of cellular regulation • Cells most often communicate with each other via chemical signals • For example, the fight-or-flight response is triggered by a signaling molecule called epinephrine External signals are converted to responses within the cell • Microbes provide a glimpse of the role of cell signaling in the evolution of life Evolution of Cell Signaling • The yeast, Saccharomyces cerevisiae, has two mating types, a and • Cells of different mating types locate each other via secreted factors specific to each type • A signal transduction pathway is a series of steps by which a signal on a cell’s surface is converted into a specific cellular response • Signal transduction pathways convert signals on a cell’s surface into cellular responses factor Receptor 1 Exchange of mating factors Communication between mating yeast cells a a factor Yeast cell, Yeast cell, mating type a mating type 2 Mating a 3 New a/ cell a/ Local and Long-Distance Signaling • Cells in a multicellular organism communicate by chemical messengers • Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells • In local signaling, animal cells may communicate by direct contact, or cell-cell recognition Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells (a) Cell junctions (b) Cell-cell recognition Communication by direct contact between cells • In many other cases, animal cells communicate using local regulators, messenger molecules that travel only short distances • In long-distance signaling, plants and animals use chemicals called hormones • The ability of a cell to respond to a signal depends on whether or not it has a receptor specific to that signal Local and long-distance cell signaling by secreted molecules in animals Local signaling Long-distance signaling Target cell Secreting cell Local regulator diffuses through extracellular fluid. (a) Paracrine signaling Electrical signal along nerve cell triggers release of neurotransmitter. Endocrine cell Neurotransmitter diffuses across synapse. Secretory vesicle Target cell is stimulated. Blood vessel Hormone travels in bloodstream. Target cell specifically binds hormone. (b) Synaptic signaling Paracrine signalling: A secreting cell acts on nearby target cells by discharging molecules of a local regulator (GF) into the extracellular fluid. Synaptic signalling: A nerve cells release neurotransmitter molecules into a synapse, stimulating the target cell. (c) Endocrine (hormonal) signaling The Three Stages of Cell Signaling: • Earl W. Sutherland discovered how the hormone epinephrine acts on cells • Sutherland suggested that cells receiving signals went through three processes – Reception – Transduction – Response Cell signaling EXTRACELLULAR FLUID 1 Reception Receptor Signaling molecule CYTOPLASM Plasma membrane Cell signaling EXTRACELLULAR FLUID 1 Reception CYTOPLASM Plasma membrane 2 Transduction Receptor Relay molecules in a signal transduction pathway Signaling molecule Cell signaling EXTRACELLULAR FLUID 1 Reception CYTOPLASM Plasma membrane 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signaling molecule Reception: A signaling molecule binds to a receptor protein, causing it to change shape • The binding between a signal molecule (ligand) and receptor is highly specific • A shape change in a receptor is often the initial transduction of the signal • Most signal receptors are plasma membrane proteins Receptors in the Plasma Membrane • Most water-soluble signal molecules bind to specific sites on receptor proteins that span the plasma membrane • There are three main types of membrane receptors – G protein-coupled receptors – Receptor tyrosine kinases – Ion channel receptors G protein-coupled receptors • G protein-coupled receptors (GPCRs) are the largest family of cell-surface receptors • A GPCR is a plasma membrane receptor that works with the help of a G protein • The G protein acts as an on/off switch: If GDP is bound to the G protein, the G protein is inactive Cell-Surface Transmembrane Receptors G protein-coupled receptor Plasma membrane Activated receptor 1 Inactive enzyme GTP GDP GDP CYTOPLASM Signaling molecule Enzyme G protein (inactive) 2 GDP GTP Activated enzyme GTP GDP Pi 3 Cellular response 4 Receptor tyrosine kinases • Receptor tyrosine kinases (RTKs) are membrane receptors that attach phosphates to tyrosines • A receptor tyrosine kinase can trigger multiple signal transduction pathways at once • Abnormal functioning of RTKs is associated with many types of cancers Signaling molecule (ligand) Ligand-binding site helix in the membrane Signaling molecule Tyrosines CYTOPLASM Tyr Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins (inactive monomers) 1 Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Tyr Dimer 2 Activated relay proteins 3 Tyr Tyr P Tyr Tyr P P Tyr Tyr P Tyr Tyr P Tyr Tyr P P Tyr Tyr P Tyr Tyr P Tyr Tyr P P Tyr Tyr P 6 ATP Activated tyrosine kinase regions (unphosphorylated dimer) 6 ADP Fully activated receptor tyrosine kinase (phosphorylated dimer) 4 Inactive relay proteins Cellular response 1 Cellular response 2 Ion channel receptors • A ligand-gated ion channel receptor acts as a gate when the receptor changes shape • When a signal molecule binds as a ligand to the receptor, the gate allows specific ions, such as Na+ or Ca2+, through a channel in the receptor Exploring: Cell-Surface Transmembrane Receptors 1 Signaling molecule (ligand) 3 2 Gate closed Ions Plasma Ligand-gated membrane ion channel receptor Gate closed Gate open Cellular response Transduction: Cascades of molecular interactions relay signals from receptors to target molecules in the cell • Signal transduction usually involves multiple steps • Multistep pathways can amplify a signal: A few molecules can produce a large cellular response • Multistep pathways provide more opportunities for coordination and regulation of the cellular response Signaling molecule Receptor Activated relay molecule Inactive protein kinase 1 Active protein kinase 1 Inactive protein kinase 2 ATP ADP P Active protein kinase 2 PP Pi Inactive protein kinase 3 ATP ADP Pi Active protein kinase 3 PP Inactive protein P ATP P ADP PP Pi Active protein Cellular response Response: Cell signaling leads to regulation of transcription or cytoplasmic activities • The cell’s response to an extracellular signal is sometimes called the “output response” Nuclear and Cytoplasmic Responses • Ultimately, a signal transduction pathway leads to regulation of one or more cellular activities • The response may occur in the cytoplasm or in the nucleus • Many signaling pathways regulate the synthesis of enzymes or other proteins, usually by turning genes on or off in the nucleus • The final activated molecule in the signaling pathway may function as a transcription factor Growth factor Reception Receptor Phosphorylation cascade Transduction CYTOPLASM Inactive transcription factor Active transcription factor P Response DNA Gene NUCLEUS mRNA • Other pathways regulate the activity of enzymes rather than their synthesis • Signaling pathways can also affect the overall behavior of a cell, for example, changes in cell shape Apoptosis integrates multiple cellsignaling pathways • Apoptosis is programmed or controlled cell suicide • Components of the cell are chopped up and packaged into vesicles that are digested by scavenger cells • Apoptosis prevents enzymes from leaking out of a dying cell and damaging neighboring cells Apoptosis of a human white blood cell 2 m • Apoptosis evolved early in animal evolution and is essential for the development and maintenance of all animals • Apoptosis may be involved in some diseases (for example, Parkinson’s and Alzheimer’s); interference with apoptosis may contribute to some cancers Effect of apoptosis during paw development in the mouse. Interdigital tissue Cells undergoing apoptosis Space between 1 mm digits Acknowledgements… The teaching material used in this lecture is taken from: JB Reece, LA Urry, ML Cain, SA Wasserman, PV Minorsky and RB Jackson. 2011. Campbell Biology (9th Edition), Publisher Pearson is gratefully acknowledged. Some information presented in this power point lecture presentation is collected from various sources including Google, Wikipedia, research articles and some book chapters from various biology books. Material and figures used in this presentation are gratefully acknowledged. This material is collected and presented only for teaching purpose. Any Questions?? Dr.Ramesh Subramani, Assistant Professor in Biology