Cell Communication and Signal Transduction PDF

Figure 11.1a © 2021 Pearson Education, Inc. Figure 11.1b © 2021 Pearson Education, Inc.  Cell Communication Cell-to-cell communication is critical for the function and survival of cells Responsible for the growth and development of multicellular organisms © Gett...

Figure 11.1a © 2021 Pearson Education, Inc. Figure 11.1b © 2021 Pearson Education, Inc.  Cell Communication Cell-to-cell communication is critical for the function and survival of cells Responsible for the growth and development of multicellular organisms © Getting Down With Science How Do Cells Communicate? Cells communicate through three general ways 1. Direct Contact 2. Local Signaling 3. Long-distance signaling © Getting Down With Science Local and Long-Distance Signaling Cells in a multicellular organism communicate via signaling molecules In local signaling, animal cells may communicate by direct contact Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells Signaling substances in the cytosol can pass between adjacent cells  Animal cells may also communicate by direct contact between cell-surface molecules Local signaling is especially important in embryonic development, immune response, and maintaining adult stem cell populations Figure 11.4  Direct Contact Direct contact: communication through cell junctions ○ Signaling substances and other material dissolved in the cytoplasm can pass freely between adjacent cells Animal cells: gap junctions Plant cells: plasmodesmata © Getting Down With Science  Direct Contact Example: ○ Immune cells Antigen presenting cells (APCs) communicate to T cells through direct contact © Getting Down With Science  Local Regulators Local regulators: a secreting cell will release chemical messages (local regulators/ligands) that travel a short distance through the extracellular fluid ○ The chemical messages will cause a response in a target cell ○ Examples: Paracrine signaling Synaptic signaling © Getting Down With Science  Local Regulators Paracrine signaling: Target cell secretory cells release local regulators (ie growth factors) Local via exocytosis to an adjacent regulator cell Secretory cell that acts on nearby cells © Getting Down With Science  In other cases, animal cells communicate using secreted messenger molecules that travel only short distances This type of local signaling in animals is called paracrine signaling Growth factors, which stimulate nearby target cells to grow and divide, are one class of such local regulators in animals  Local Regulators Synaptic signaling: Occurs Axon in animal nervous systems Neurons secrete Neurotransmitters neurotransmitters ○ Diffuse across the synaptic cleft- space between the nerve Synaptic cleft cell and target cell Target cell © Getting Down With Science  Synaptic signaling occurs in the animal nervous system when a neurotransmitter is released in response to an electric signal Drugs used to treat depression, anxiety, and post-traumatic stress disorder (PT SD) affect this signaling process Figure 11.5  Long Distance Signaling Animals and plants use hormones for long distance signaling ○ Plants release hormones that travel in the plant vascular tissue (xylem and phloem) or through the air to reach target tissues ○ Animals use endocrine signaling Specialized cells release hormones into the circulatory system where they reach target cells © Getting Down With Science  In long-distance signaling, plants and animals use molecules called hormones In hormonal (or endocrine) signaling in animals specialized cells release hormones, which travel to target cells via the circulatory system 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 Example: ○ Insulin Insulin is released by the pancreas into the bloodstream where it circulates through the body and binds to target cells © Getting Down With Science  Quick Check 1. What type of communication involves a cell secreting a substance to an adjacent target cell? a. Answer: paracrine signaling 2. Plant cells in direct contact with each other can diffuse substances through these structures to communicate. What are they? a. Answer: plasmodesmata © Getting Down With Science  Practice Problems Work on practice problems 1-7 in your packet © Getting Down With Science  Think, Pair, Share How do you think cells process signals? © Getting Down With Science  Cell Signaling: Overview Cell-to-cell messages can be divided into three stages 1. Reception ○ Ligand binds to receptor © Getting Down With Science  Cell Signaling: Overview Cell-to-cell messages can be divided into three stages 1. Reception ○ Ligand binds to receptor 2. Transduction ○ Signal is converted © Getting Down With Science  Cell Signaling: Overview Cell-to-cell messages can be divided into three stages 1. Reception ○ Ligand binds to receptor 2. Transduction ○ Signal is converted 3. Response ○ A cell process is altered © Getting Down With Science A B C The Three Stages of Cell Signaling: A Preview Earl W. Sutherland and colleagues discovered how the hormone epinephrine acts on cells Sutherland’s work suggested that cells receiving signals went through three processes ○ Signal Reception ○ Signal Transduction ○ Cellular Response  In reception, the target cell detects a signaling molecule that binds to a receptor protein on the cell surface In transduction, the binding of the signaling molecule alters the receptor and initiates a signal transduction pathway; transduction often occurs in a series of steps In response, the transduced signal triggers a specific response in the target cell Figure 11.6 Animation: Overview of Cell Signaling © 2021 Pearson Education, Inc.  Stage 1: Reception Reception: the detection and receiving of a ligand by a receptor in the target cell Receptor: macromolecule that binds to a signal molecule (ligand) ○ All receptors have an area that interacts with the ligand and an area that transmits a signal to another protein Binding between ligand and receptor is highly specific © Getting Down With Science  Stage 1: Reception When the ligand binds to the receptor, the receptor activates (via a conformational change) Allows the receptor to interact with other cellular molecules ○ Initiates transduction signal Receptors can be in the plasma membrane or intracellular © Getting Down With Science  Stage 1: Reception Plasma Membrane Receptors Intracellular Receptors Most common type of Found in the cytoplasm or receptor involved in nucleus of target cell signal pathways Bind to ligands that can Bind to ligands that are: pass through the plasma ○ Polar, water-soluble membrane ○ Large ○ Ie hydrophobic Examples: molecules ○ G protein coupled receptors (GPCRs) Steroid and thyroid ○ G protein-coupled receptors (GPC hormones Rs) are the largest family of cell- Gasses like nitric surface receptors ○ Ligand-gated ion channels © Getting Down With Science oxide Figure 11.8b  Stage 1: Reception Intracellular receptors Note: the AP exam will not expect you to be able to classify any given molecule as hydrophobic, usually they will either tell you it is hydrophobic, or they will say the molecule is a steroid hormone © Getting Down With Science Intracellular Receptors Intracellular receptor proteins are found in the cytoplasm or nucleus of target cells Small or hydrophobic chemical messengers can readily cross the membrane and activate receptors Examples of hydrophobic messengers are the steroid and thyroid hormones of animals An activated hormone-receptor complex can act as a transcription factor, turning on or off specific genes Figure 11.9  Stage 2: Transduction Transduction: the conversion of an extracellular signal to an intracellular signal that will bring about a cellular response Requires a sequence of Intracellular changes in a series of signaling molecules molecules known as a signal transduction pathway © Getting Down With Science  Stage 2: Transduction The signal transduction pathway regulates protein activity through: ○ Phosphorylation by the enzyme protein kinase Relays signal inside cell ○ Dephosphorylation by the enzyme protein Intracellular signaling molecules phosphatase Shuts off pathways *Remember: a change in shape means a change in function © Getting Down With Science  Stage 2: Transduction During transduction the signal is amplified Second messengers: small, non-protein molecules and ions help relay the message and amplify the response ○ Cyclic AMP (cAMP) is Intracellular signaling molecules a common second messenger © Getting Down With Science  Stage 3: Response Response: the final molecule in the signaling pathway converts the signal to a response that will alter a cellular process Examples: A. Protein that can alter membrane permeability B. Enzyme that will change a metabolic process C. Protein that turns genes on or off A © Getting Down With Science B C  Quick Review 1. What are the three stages of cell signaling? a. Answer: reception, transduction, reponse 2. What is the actual “signal” being transduced in a signal transduction pathway? a. Answer: a ligand 3. How is this “signal” passed from outside to inside the cell? a. Answer: through transduction. During transduction the signal is relayed by protein kinases and amplified by second messengers © Getting Down With Science Signal Transduction Pathways Signal transduction pathways can influence how a cell responds to its environment ○ They can result in changes in gene expression and cell function Can alter phenotypes or result in cell death © Getting Down With Science  Changes in Signal Transduction Pathways Mutations to receptor proteins or to any component of the signaling pathway will result in a change to the transduction of the signal © Getting Down With Science  Practice FRQ Some diseases, such as cancer and diabetes, are caused by defective protein phosphatases. Explain how such a defective protein would affect a signal transduction pathway. © Getting Down With Science  Important Receptors In eukaryotic organisms there are two main categories of cell membrane receptors: G protein coupled receptors (GPCRs) Ion channels © Getting Down With Science  GPCRs G protein coupled receptors (GPCRs): Largest category of cell surface receptors Important in animal sensory systems Binds to a G protein that can bind to GTP, which is an energy molecule similar to ATP GPCR © Getting Down With Science  GPCRs The GPCR, enzyme, and G protein are inactive until ligand binding to GPCR on the extracellular side Inactive ligand enzyme Inactive G protein Inativate GPCR © Getting Down With Science  GPCRs Ligand binding causes cytoplasmic side to change shape ○ Allows for the G protein to bind to GPCR Activates the GPCR and G protein GDP becomes GTP Inactive Ligand enzyme binds Active G protein Active GDP GPCR becomes © Getting Down With Science GTP  GPCRs Part of the activated G protein can then bind to the enzyme ○ Activates enzyme ○ Amplifies signal and leads to a cellular response Active enzyme Signaling © Getting Down With Science pathway  Ion Channels Ligand gated ion channels: Located in the plasma membrane Important in the nervous system Receptors that act as a “gate” for ions ○ When a ligand binds to the receptor, the “gate” opens or closes allowing the diffusion of specific ions Initiates a series of events that lead to a cellular response © Getting Down With Science Ion Channels © Getting Down With Science  A ligand-gated ion channel receptor acts as a gate that opens and closes 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 Figure 11.8d