Cellular Signalling - Notes

direct contact Cellular Signalling cell junctions cell-surface molecules Cells in a multicellular organism communicate via signaling molecules long-distance signaling local signaling In long-distance signaling, plants and animals use molecules called hormones The Three Stages of Cell Signaling : In hormonal (orendocrine) signaling in animals specialized cells release hormones, which travel to target cells via the circulatory system 1-Signal Reception Local signaling is especially important in embryonic main types of membrane receptors 2- Signal Transduction A shape change in a receptor is generally the initial transduction of the signal Most signal receptors are plasma membrane proteins, but others are located inside the cell stem cell populations G protein-coupled receptors ( GPCRs ) G protein-coupled receptors (GPCRs) are cell-surface transmembrane receptors that work with the help of a G protein The activated receptor activates another protein, which activates another, and so on, until the protein producing the response is activated At each step, the signal is transduced into a different form, commonly a shape change in a protein The response may occur in the nucleus or in the cytoplasm Remove P from protein Phosphorylation and dephosphorylation of proteins are commonly used in cells to regulate protein activity Many signaling pathways regulate the synthesis of enzymes or This phosphorylation and dephosphorylation system acts as a molecular switch, turning activities on and off, or up or down, as required proteins, usually by turning genes on or off in the nucleus Protein kinases The final activated molecule in the signaling pathway may phosphorylation function as a transcription factor* I Many relay molecules in signal transduction pathways are Protein phosphatases Abnormal functioning of RTKs is associated with many types of cancers Receptor tyrosine kinases (RTKs) are membrane receptors that catalyze the transfer of phosphate groups from ATP to another protein transcription factor: is any protein that binds to DNA and controls gene expression protein kinases, creating a phosphorylation cascade G proteins bind the energy-rich GTP dephosphorylation Protein phosphatases rapidly remove the phosphates from A receptor tyrosine kinase can trigger multiple signal transduction pathways at once proteins, a process called dephosphorylation 3 Small Molecules and Ions as Second Messengers Are small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion Second messengers participate in pathways initiated by ( GPCRs and RTKs ) Ion channel receptors 1- Cyclic AMP (cAMP) 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 Ca + 2 21 a small molecule produced from ATP, and one of the most widely used second messengers 33 Adenylyl cyclase an enzyme in the plasma membrane, converts ATP to cAMP in response to an extracellular signal Intracellular Receptors 2- Calcium Ions and Inositol Triphosphate ( IP ) Calcium is an important second messenger because cells can 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 Calcium ions ( Ca ) act as a second messenger in many pathways 21J - Intracellular receptor proteins are found in the cytoplasm or nucleus of target cells released in response to an a signal transduction pathway leads to regulation of one or more cellular activities Protein Phosphorylation and Dephosphorylation to protein, a process called phosphorylation bad when a neurotransmitter is Nuclear and Cytoplasmic Responses Protein kinases transfer phosphates from ATP 2 the animal nervous system 3- Cellular Response Cascades of molecular interactions transmit signals from receptors to relay molecules in the cell 3 Receptor tyrosine kinases ( RTKs ) using secreted messenger Synaptic signaling occurs in electric signal The binding of a signaling molecule to a receptor triggers the first step in a chain of molecular interactions The G protein acts as an on/off switch: If GDP is bound to the G protein, the G protein is inactive regulate its concentration : A signal relayed by a signal transduction pathway may trigger an increase in calcium in the cytosol Pathways leading to the release of calcium involve inositol triphosphate ( IP3 ) and diacylglycerol ( DAG ) as additional second messengers If Synaptic signaling paracrine signaling class of such local regulators in animals f P from ATP to protein FB ÷ development, immune response, and maintaining adult target cells to grow and divide, are one a. The binding between a signal molecule (ligand) and receptor is highly specific bad contact between cell-surface molecules between adjacent cells Growth factors , which stimulate near by signaling molecule binds to a receptor protein, causing it to change shape 2 Animal cells may also communicate by direct molecules that travel only short distances whether or not it has a receptor specific to that signal bad connect the cytoplasm of adjacent cells animal cells communicate using secreted messenger The ability of a cell to respond to a signal depends on ⇐ Animal and plant cells have cell junctions that directly Signaling substances in the cytosol can pass Many signal molecules trigger formation of cAMP Other components of cAMP pathways are G proteins, G protein-coupled receptors, and protein kinases cAMP usually activates protein kinase A,which phosphorylates various other proteins Other pathways may regulate the activity of proteins rather than their synthesis (a cytoplasmic response) Inactivation mechanisms are an essential aspect of cell signaling When signal molecules leave the receptor,the receptor reverts to its inactive state and therefore the signal is terminated (switched off)