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Chapter 11: Cell Communication Objectives The student is responsible for: 1.The definitions of all bold faced words in the chapter 2.Knowing the entire chapter. 3.Diagrams of some importance: 11.1, 11.6, 11.8 4.Diagrams of moderate import: 11.3, 11.12, 11.14, 11.19 5.Diagrams of huge importance: 11.4, 11.5, 11.7, 11.9, 11.10, 11.11, 11.13, 11.15, 11.16, 11.17, 11.18 Other Notes: this is a very technical chapter, the most yet. You should read it slowly, carefully and in small bits and pieces and review these bits and pieces nightly. I expect you to have plenty of questions... So ask!
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Figure 11.0 Yeast Could this just be a picture of a bunch of lemons? I think not.
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Science Demystifies Sex!!! It’s just a response to chemical messages. Oh wait! That’s in yeast! Whew! Each yeast cell secretes a type of chemical, a or α, and these bind to receptors that cause the two yeast cells to move towards each other. Bingo! And how does that simple binding of the mating factor to a receptor elicit the cellular response of “moving towards each other?” It’s our good friend, the Signal Transduction Pathway.
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Figure 11.2 Communication among bacteria Bacteria can share info about nutrient availability. Scarce food causes aggregation and then the bacteria “go into hiding” by forming spores and becoming dormant.
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Video 15.2: Molecular Biology of the Cell Video 15.3: Neutrophil Chase (Molecular Biology of the Cell)
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Cell to Cell Communication May Occur Via: 1.Paracrine signaling: where a chemical messenger is released from a cell and affects several nearby surrounding cells. 2.Synaptic Signaling such was with nerves 3.Hormones which are either peptide or steroidal molecules, secreted in small amounts into the bloodstream, and travel long distances to affect their targets 4.Cell to cell contact via gap junctions (animals) or plasmodesmata (plants) 5.Cell-to-Cell recognition where molecules on a cell’s surface recognize and bind to molecules on another cell’s surface.
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Figure 11.3 Local and long-distance cell communication in animals Paracrine signaling: several cells can be affected at once. Synaptic signaling: more specific (nerve cell to nerve cell) Hormonal signaling: signals sent over long distances and can affect several target cells.
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Figure 11.4 Communication by direct contact between cells
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Just exactly how are these cell signals converted into a cellular response? 1.Reception: usually the signal molecule binds to a cell membrane surface receptor or a receptor within the cytosol. 2.Transduction: the receptor protein is altered and this begins a series of biochemical reactions leading to the cellular response. 3.Response: the elicitation of the cellular response.
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Figure 11.5 Overview of cell signaling (Layer 3)
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Figure 11.6 The structure of a G-protein-linked receptor G proteins interact with guanosine triphosphate (GTP) Transmembrane Protein
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Figure 11.7 The functioning of a G-protein-linked receptor
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Tyrosine-Kinase Receptors 1.These receptors for growth factors 2.They have enzymatic activity; the part on the cytoplasmic side acts as an enzyme, tyrosine kinase. 3.A “kinase” is an enzyme that moves a phosphate group onto a protein. 4.A tyrosine kinase receptor therefore, when activated, moves a phosphate group onto the amino acid tyrosine.
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How Does This Tyrosine-Kinase Receptor Work? 1.The receptor is made of two identical, but separate, parts called monomers. 2.Signal molecules bind to the extracellular aspect of the receptor and cause the monomers to form a dimer. 3.ATP now phosphorylates the tyrosines which are on the cytoplasmic side of the membrane protein. 4.This phosphorylation causes the activation of other intracellular proteins leading to the desired cellular response through a signal transduction pathway.
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Figure 11.8 The structure and function of a tyrosine-kinase receptor
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Figure 11.9 A ligand-gated ion-channel receptor These channels are protein pores that open when the signal molecule or ligand binds. The ion change on the inside of the cell causes a cellular response (nerve cells)
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Figure 11.10 Steroid hormone interacting with an intracellular receptor Some signal molecules can pass through the cell membrane. The hormone-receptor complex will activate transcription factors that turn on specific genes in the DNA.
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Figure 11.11 A phosphorylation cascade A Cascade of Phosphorylation
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Figure 11.17 Nuclear response to a signal: the activation of a specific gene by a growth factor And many times that cellular response is dependent on activating a gene.
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Second Messengers 1.cAMP or cyclic AMP ATP is converted to cAMP by the enzyme adenyl cyclase Example: when epinephrine binds to muscle cells cAMP becomes inactive by being converted to AMP But in the case of cholera, caused by feces contaminated water (pg 208), cAMP is not inactivated and the intestine secretes large amounts of water into the intestine.
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Figure 11.12 Cyclic AMP
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Figure 11.13 cAMP as a second messenger
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Second Messengers (cont’d) 2.Calcium ions Used in muscle contraction and cell division In muscle cells, calcium will bind to calmodulin which activates other proteins to elicit a cellular response. In plant cells, calcium ions are a second messenger to signal changes during drought or cold conditions.
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Figure 11.14 The maintenance of calcium ion concentrations in an animal cell
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Second Messengers (cont’d) 3.Diacylglycerol (DAG) and Inositol Triphosphate Both are formed from the breakdown (hydrolysis) of another compound PIP2 (a phospholipid in the cell membrane). IP 3 helps to release calcium from the sarcoplasmic reticulum in muscle cells. IP3 will diffuse through the cytosol, open IP3-regulated Ca 2+ ion gates causing calcium to be released into the cytosol. DAG can exert two signals. The synthesis of prostaglandins (inflammatory response). Most anti-inflammatory drugs (aspirin, ibuprofen and cortisone) act to inhibit synthesis of prostaglandins. DAG activates a protein kinase.
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Figure 11.15 Calcium and inositol triphosphate in signaling pathways (Layer 3)
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Ca will trigger: sperm cell block in a fertilized egg. onset of embryonic development. muscle contraction secretion of cellular products.
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Figure 11.16 Cytoplasmic response to a signal: the stimulation of glycogen breakdown by epinephrine Adrenaline activates at least 9 different receptor G-protein linked receptors. Mice have about 1000 G-protein linked receptors just for their sense of smell. About half of all drugs work through G-protein linked receptors.
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Figure 11.17 Nuclear response to a signal: the activation of a specific gene by a growth factor
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Figure 11.18 The specificity of cell signaling Notice that the relay molecules are different and these different molecules control the kind or type of response. So a liver cell can store glucose or breakdown glycogen to glucose depending on the signal molecule and relay protein. Different kinds of cells have different collections of proteins
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Scaffolding Proteins or What Keeps All These Continuums of Molecules Close Together Large proteins serve to hold several relay proteins close by The scaffolding serves to carry the protein kinases when they are activated by the membrane receptor. So if the scaffolding framework is “bad” then this cascade of events can’t occur, genes are activated and you have genetic disorders (diseases)
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Figure 11.19 A scaffolding protein
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