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BIO 110 (1)

Cell Signaling

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BIO 110
Sarah Learman

Cell Signaling Chapter 11 Local and Long-Distance Signaling • Cells communicate by chemical messengers – “Ligand” or signal molecule • Cells have receptor proteins that ligands bind to – On cell membrane or inside the cell – three-dimensional shape – fits a specific ligand • When a ligand and receptor protein bind, a ___________ ___________ in the receptor protein is induced and a response in the cell is generated Receptor + Ligand = Signal Ligand = Cellular Response Receptor Protedin Off On How Do Cell’s Communicate? • Local Signaling: • Direct Contact: – Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells • Gap Junctions (Animal Cells) • Plasmodesmata (Plant Cells) – Animal cells may also communicate by Cell-Cell Recognition • Ligand is bound to the membrane of another cell Plasma membranes Gap junctions Plasmodesmata between animal cells between plant cells (a) Cell junctions (b) Cell-cell recognition How Do Cell’s Communicate? • Local Signaling – When animal cells do not come in direct contact with each other they communicate using local regulators, messenger molecules that travel only short distances – Paracrine signaling – a cell acts on nearby target cells by secreting signal molecules into the extracellular fluid • Circular perfume example – Synaptic signaling – a nerve cell releases neurotransmitter molecules into a synapse (area between two cells), stimulating the target cell Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter. Neurotransmitter Secreting Secretory diffuses across cell vesicle synapse. Local regulator diffuses through Target cell extracellular fluid. is stimulated. (a) Paracrine signaling (b) Synaptic signaling How Do Cell’s Communicate? • Long-distance signaling – plants and animals use chemicals called hormones • Specialized endocrine cells secrete hormones into the body fluids, often blood. Hormones reach virtually all body cells, but only affect specific target cells, triggering a response • The ability of a cell to respond to a signal depends on whether or not it has a receptor specific to that signal Long-distance signaling Only target cells have the receptor proteins and are Endocrine cell Blood able to receive the vessel signal (bind the ligand) Hormone travels in bloodstream. Target cell specifically binds hormone. (c) Endocrine (hormonal) signaling Reception - Receiving the Signal EXTRACELLULAR CYTOPLASM FLUID Plasma membrane 1 Reception Receptor Signaling molecule Reception - Receiving the Signal • Hormones vary widely – size – Shape – Type (chemistry!) • Hydrophilic hormones can not pass through the plasma membrane and bind to receptor located on the surface of the cell • Hydrophobic hormones enter the cell and bind to receptors inside the cell Reception – Receiving the signal • Gated ion channels open or close in response to signal binding 1 2 3 Gate Ions Gate Gate closed Signaling closed open molecule (ligand) Ligand-gated Plasma ion channel receptorembrane Cellular response Reception – Receiving the signal • Enzyme receptors catalyze biological reactions on the membrane G protein-coupled Plasma Activated Signaling Inactive membrane receptor molecule enzyme receptor GTP GDP GDP CYTOPLASM G protein Enzyme GTP 1 (inactive) 2 GDP Activated enzyme GTP GDP P i 3 Cellular response 4 Transduc
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