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JAK/STAT signalling •
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Binding of cytokines (small protein ligands) to the cytokine receptor causes dimerisation (two receptor molecules come together to form a complex). Janus Kinase (JAK) is a receptor-­‐associated tyrosine kinase. Kinases are enzymes that modify other proteins by phosphorylation. Lots of signalling pathways involve activation and inactivation of proteins by kinases adding and phosphatases removing phosphate groups. JAK transfers phosphate groups onto tyrosine residues on STAT. Two JAKs phosphorylate each other and then each phosphorylates a receptor monomer. Two STATs can then bind to the receptor. •
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Signal Transducer and Activator of Transcription (STAT) proteins are latent transcription factors, always present in the cytoplasm, ready to be activated by JAK. Two phosphorylated STATs form a dimer: this is an active transcription factor. It moves to the nucleus and binds to a specific target gene sequence (promoter) that regulates transcription of the gene. 1 4 5 6 8 10 12 14 15 16 2 3 7 9 11 13 ACROSS Only switched on in response to a signal (applies to signalling proteins and to genes) Enzymes that phosphorylate other proteins The idea that DNA makes RNA which makes protein An intermediate in signalling pathways that transmits the signal Does the opposite to a kinase The set of all mRNA molecules in a cell or population of cells When a cell secretes a chemical messenger that binds to receptors on that same cell Signalling between cells in direct contact via junctions or membrane-­‐
tethered ligands Produced by faulty signalling leading to uncontrolled cell division Describes a substance or process that originates from within an organism, tissue or cell DOWN A biochemical chain of events inside the cell leading to a response Protein that binds to DNA to control its expression Cells that communicate with each other electrically through synapses An amino acid that is often a target for kinases Ligands bind to these Created by the association of two proteins