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Describa la imagen:
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Figure 15–3 The binding of extracellular signal molecules to either cell-surface or intracellular receptors. (A) Most signal molecules are hydrophilic and are therefore unable to cross the target cell’s plasma membrane directly; instead, they bind to cell-surface receptors, which in turn generate signals inside the target cell (see Figure 15–1). (B) Some small signal molecules, by contrast, diffuse across the plasma membrane and bind to receptor proteins inside the target cell— either in the cytosol or in the nucleus (as shown here). Many of these small signal molecules are hydrophobic and nearly insoluble in aqueous solutions; they are therefore transported in the bloodstream and other extracellular fluids bound to carrier proteins, from which they dissociate before entering the target cell.
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¿Cómo se llama este tipo de comunicación?
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Paracrina:
depende de las señales que se liberan al espacio extracelular y actúa de forma local en células vecinas |
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¿Qué tipo de señalizacion es?
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| Endocirna, las celulas liberna hormonas al torrente sanguieno, se distribuyen por el cuerpo |
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[image]
Trate de describir el proceso |
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| Figure 15–6 Extracellular signals can act slowly or rapidly to change the behavior of a target cell. Certain types of signaled responses, such as increased cell growth and division, involve changes in gene expression and the synthesis of new proteins; they therefore occur slowly, often starting after an hour or more. Other responses—such as changes in cell movement, secretion, or metabolism—need not involve changes in gene transcription and therefore occur much more quickly, often starting in seconds or minutes; they may involve the rapid phosphorylation of effector proteins in the cytoplasm, for example. Synaptic responses mediated by changes in membrane potential can occur in milliseconds (not shown). |
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| El ligando activa el receptor, la actividad de la célula en respuesta puede ser lenta o rápida: rápida por proteínas del citoplasma, lenta porque acriva factores de transc --> trans de genes --> síntesis de RNa-->cambio de morfología de la célula |
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describa la imágen
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| Figure 15–14 The nuclear receptor superfamily. All nuclear receptors bind to DNA as either homodimers or heterodimers, but for simplicity we show them as monomers here. (A) The receptors all have a related structure. Here, the short DNA-binding domain in each receptor is indicated in light green. (B) An inactive receptor protein is bound to inhibitory proteins. Domain-swap experiments suggest that many of the ligand-binding, transcription-activating, and DNA- binding domains in these receptors can function as interchangeable modules. (C) Receptor activation. Typically, the binding of ligand to the receptor causes the ligand-binding domain of the receptor to clamp shut around the ligand, the inhibitory proteins to dissociate, and coactivator proteins to bind to the receptor’s transcription-activating domain, thereby increasing gene transcription. In other cases, ligand binding has the opposite effect, causing co-repressor proteins to bind to the receptor, thereby decreasing transcription (not shown). Though not shown here, activity can also be controlled through a change in the localization of the receptor: in its inactive form, it can be retained in the cytoplasm; ligand binding can then lead to the uncovering of nuclear localization signals that cause it to be imported into the nucleus to act on DNA. (D) The three-dimensional structure of a ligand-binding domain with (right) and without (left) ligand bound. Note that the blue a helix acts as a lid that snaps shut when the ligand (shown in red) binds, trapping the ligand in place. |
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wo types of intracellular signaling proteins that act as molecular switches. Although one type is activated by phosphorylation and the other by GTP binding, in both cases the addition of a phosphate group switches the activation state of the protein and the removal of the phosphate switches it back again.
(A) A protein kinase covalently adds a phosphate from ATP to the signaling protein, and a protein phosphatase removes the phosphate. Although not shown, some signaling proteins are activated by dephosphorylation rather than by phosphorylation. (B) A GTP- binding protein is induced to exchange its bound GDP for GTP, which activates the protein; the protein then inactivates itself by hydrolyzing its bound GTP to GDP. |
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| Figure 15–22 A specific signaling complex formed using modular interaction domains. This example is based on the insulin receptor, which is an enzyme-coupled receptor (a receptor tyrosine kinase, discussed later). First, the activated receptor phosphorylates itself on tyrosines, and one of the phosphotyrosines then recruits a docking protein called insulin receptor substrate- 1 (IRS1) via a PTB domain of IRS1; the PH domain of IRS1 also binds to specific phosphoinositides on the inner surface of the plasma membrane. Then, the activated receptor phosphorylates IRS1 on tyrosines, and one of these phosphotyrosines recruits the adaptor protein (Grb2) via an SH2 domain of Grb2. Next, Grb2 uses one of its two SH3 domains to bind to a proline-rich region of the monomeric GTPase-activating protein called Sos (a Ras-GEF, discussed later), which also binds to phosphoinositides in the plasma membrane via its PH domain. Grb2 uses its other SH3 domain to bind to a proline- rich sequence in a scaffold protein. The scaffold protein binds several other signaling proteins, and the other phosphorylated tyrosines on IRS1 recruit additional signaling proteins that have SH2 domains (not shown). |
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