sravanti master seminar - MASTER SEMINAR ON SIGNAL...

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MASTER SEMINAR ON SIGNAL TRANSDUCTION, CANCER AND CELL AGEING PRESENTED BY, K. Sravanti, RAM/12-48.
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SIGNAL TRANSDUCTION
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The environment or a cell sends a message to another cell in the form of signaling molecules. These signaling molecules may be hormones, growth factors or cytokines. Signals, which originate from environment, may be temperature, osmolarity, or ions like iron etc. In order to respond, the recipient or the target cells must receive these signals through receptors. The signal may be transmitted directly or via a cascade pathway involving many proteins.
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COMPONENTS OF SIGNAL TRANSDUCTION Ligand : A molecule that binds to a specific site on another molecule, usually a protein, i.e, receptor. Receptor The protein to which the ligand binds is known as receptor. Effector molecules : Protein kinases or phosphatases, Transcription factors Secondary messengers : Ca 2+ , G-proteins, Inositol Phosphate Response : Stomatal closure, Change in growth direction etc.
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Generic Signal Transduction
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When a signaling molecule attaches with its specific receptors on target cells signal is transmitted from cell membrane to nucleus. The signal may be transmitted directly or via a cascade pathway involving many proteins. These pathways between the cell membrane and the cell nucleus are called signal transduction pathways.
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Generic Signalling Pathway Signal Receptor (sensor) Transducti on Cascade Targets Response Altered Metabolis m Metabolic Enzyme Gene Regulator Cytoskeletal Protein Altered Gene Expression Altered Cell Shape or Motility Adapted from Molecular Biology of the Cell,(2002), 4th edition, Alberts et al.
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DIFFERENT PATHWAYS 1.G PROTEIN-COUPLED RECEPTORS. 2.PROTEIN-TYROSINE PHOSPHORYLATION AS A MECHANISM FOR SIGNAL TRANSDUCTION.
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G-Protein Coupled Receptors G proteins are heterotrimers having one copy each of α, β and γ- subunits. The trimer state of G proteins is inactive, and is stabilized by an association of a GDI molecule to the single guanine nucleotide binding site (site to which GDP and GTP bind of α subunit)
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G PROTEIN ACTIVATION Many hormone and other receptors generate signal transduction by activating G proteins. Binding of ligand activates the receptor .The activated receptor interacts with G protein and causes its GDP to be replaced by GTP; this activates the G protein Activated G protein acts on the target protein, usually an enzyme, which is either activated or inhibited. The target enzymes are called effector enzymes . These are membrane bound. Some activated effector proteins lead to the production of a small molecule(second messenger) which activate a variety of pathways.
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Essential features of signal transduction mediated by G proteins RECEPTOR LIGAND ACTIVATED RECEPTOR GDP. α βγ βγ + α GTP INACTIVE G PROTEIN ACTIVE G PROTEIN α . GTP ACTIVE EFFECTOR ENZYME INACTIVE EFFECTOR ENZYME
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G Proteins and Effector Proteins
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EPINEPHRINE SIGNAL-β –ADRENERGIC RECEPTOR PATHWAY
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Epinephrine Influence The Breakdown of Glycogen
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IP 3 -Mediated Signal Transduction
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