Ap Biology Notes Cellular Communication Essay Example for Free

Ap Biology Notes Cellular Communication EssayCell-to- cadre communication is essential in multi cellph cardinalular organisms. They must communicate to coordinate typifyivities such as proceeds and development, and reproduction. In addition unicellular organisms communicate with each separate. Signals may use light, or touch but we will focus on chemical point outs.1. orthogonal signals are converted to responses within the cell a. Evolution of cell intercommunicate i. In barm a cells and cells both secrete chemicals, which butt totally be received by the alternate type yeast. This signals the two cells to join via fusion 1. The process by which the signal on the surface of the cell is converted to a series of steps by the cell in response is called a signal transduction pathway ii. Signal transduction pathways are very similar in yeast and in complex multicellular organisms 2. This leads scientists to believe that this pathway evolved first in ancient prokaryotes b. Lo cal and long distance polarity iii. Local signaling3. neighboring cells of plants and animals may communicate through cell junctions a. Signaling substances dissolved in the cytoplasm travel between cells i. Plants = plasmodesmataii. Animals = gap junctions4. Animal cells may use the side by side(p)b. Cell-to-cell recognitioniii. Direct contact between membrane-bound cell-surface molecules iv. Important in embryonic development and immune responsec. Paracrine signalingv. Uses local regulators which are released and travel only a short distance to nearby cells vi. Ex. Growth factors coffin nail nearby cells to grow and divide d. Synaptic signalingvii. Electrical signal along a nerve cell triggers a chemical release across a synapse to trigger response in target cell viii.Ex. Nerve cellsiv. Long- distance signaling5. Both plants and animals use hormonese. Animals (endocrine signaling) cells release hormones which travel in the circulatory system to target cells f. Plants hormones travel in vessels or by diffusion through the g grim as gas g. Hormones vary in size and traffic pattern6. Nervous system signals can also be long distance c. The three stages of cell signaling A previewv. Reception when the target cell detects a signaling molecule. The signaling molecule binds to a receptor protein on the target cells surface vi. Transduction After binding the receptor protein is changed in some way, this converts the signal to a form that will bring about a unique(predicate) cellular response7. May occur in a single step or a series of changes vii. Response The transduced signal triggers a specific cellular response. 8. Catalysis of an enzyme, rearrangement of the cytoskeleton, activation of a specific gene 2. Reception A signaling molecule binds to a receptor protein, causing it to change shape d. To ensure signals are sent to the correct cell signaling molecules act as a ligand. viii. Ligand- molecule that specifically binds to another (usually larger) molec ule ix. The receptor protein thence usually changes shape x. May be located on the membrane or inside the cell e. Receptors in the plasma membranexi. Water-soluble signaling molecule binds to receptor on the membrane causing it to change shape or aggregate. f. Intracellular Receptors xii. Found in cytoplasm or nucleus of target cells9. Signaling molecule must be hydrophobic enough or small enough to pass through the plasma membrane h. Steroid hormones, thyroidal hormones, nitric oxide Examples Pathway OtherG-Protein Coupled Receptors Yeast junction factors, epinephrine, hormones, neurotransmitters 1. signaling molecule binds to the g-protein receptor 2. receptor changes shape and the cytoplasmic side binds to the inactive G protein 3. GTP then displaces to form GDP and activates the protein 4. Activated G protein diffuses along the membrane to an enzyme altering the enzyme to trigger the next step Bacteria such as whooping cough, botulism and epidemic cholera disrupt this pathwa y Receptor Tyrosine Kinases Enzymes that catalyze the transfer of phosphate groups 1. binding of two signaling molecules to two tyrosine chains causes the two to associate with each other forming a dimer2. dimerization activates the tyrosine kinase region to add a phosphate from and ATP to each tyrosine in the polypeptide 3. each tail can now bind to and activate a different specific relay protein within the cell One receptor may activate ten+ pathways. Absence can result in pubic louse Ion Channel Receptors Nervous system 1. signaling molecule binds to the ion get in the membrane 2. protein changes shape creating a channel through the membrane 3. specific ions can now flow through the membrane which may cause a change in the cell or trigger another pathway most ion gated channels are controlled by change in voltage rather than binding of a ligandg. Intracellular Receptorsxiii. Ex. Testosterone10. Hormone passes through the plasma membrane 11. Testosterone binds to a receptor pro tein in the cytoplasm activating it 12. The hormone-receptor complex enters the nucleus and binds to a specific gene 13. The bound protein acts as a arrangement factor, stimulating the transcription of the gene into mRNA 14. The mRNA is translated into a specific protein 3. Transduction cascades of molecular interactions relay signals from receptor to target molecules in the cell h. Protein phosphorylation and dephosphorylationxiv. Proteins can be trigger by the addition of a phosphate group (often broken off of ATP or GTP) 15. Phosphates are transferred from ATP to a protein by a global group of enzymes known as protein kinases i. Phosphorylation often causes the protein to change shape j. This happens because the added phosphate group interacts with polar or charged amino acids within the protein xv. Protein phosphatases are enzymes that sequestrate phosphate groups from a protein 16. Mechanism for turning off signal transduction 17. These also allow for turning off and reusin g pathways i. Small molecules and ions as second messengersxvi. Molecules other than proteins act as second messengers 18. Small and water soluble such as ionsk. This allows them to rapidly spread throughout the cell via diffusion 19. Second messenger refers to anything by and by the first messenger which is the extracellular signaling molecule that binds to the membrane 20. Most common second messengers are cyclic AMP and Ca+2 xvii. cyclic AMP as a second messenger in response to the hormone epinephrine 21. Epinephrine binds to receptor molecule protein activates adenylyl cyclase which can catalyze the implication of many molecules of cAMP l. Adenylyl cyclase catalyzes the conversion of ATP into cAMP ix. cAMP usually activates a serine/threonine kinase known as protein kinase A which phosphorylates many other proteins m. cAMP is converted back to AMP by phosphodiesterase xviii. Calcium ions and inositol tripohosphate22. Increasing calcium concentration causes responses such as m uscle contraction, secretion of substances, and cell division in animals, and discolor in response to light in plants 23. Calcium is usually in high concentrations outside of the cell and in the ER but in low concentrations in the cytosol 24. Pathwayn. Signaling molecule binds to receptor o. Phospholipid pinches off membrane IP3 is released as second messenger p. IP3 binds to receptor on ER causing protein channel to open q. Ca+2 is released into cytosol4. Response Cell signaling leads to regulation of transcription or cytoplasmic activities j. Nuclear and cytoplasmic responsesxix. Pathways lead to the regulation of one or more cellular activities25. Regulate protein synthesisr. Turning specific genes on or off (calls for the synthesis of mRNA from DNA)26. Regulate protein activitys. drive a shape change to turn a protein on or off27. Regulate overall shape change of cell28. Release of mating factors29. Cell divisionk. Fine-tuning of the responsexx. Signal amplification30. Enzyme cascades amplify effects by increasing the product at each step t. Enzymes sting active long enough to work on multiple products before becoming inactive xxi. The specificity of cell signaling and coordination of the response 31. Different types of cells are programmed to reply to only certain types of signals u. Some cells will respond to the same signals but in different ways v. This is because different cells have different collections of proteins xxii. Signaling cogency scaffolding proteins and signaling complexes32. Scaffolding proteins increase the efficiency of the response w. A large protein with multiple protein kinases attached x. Decreases the time of the response because diffusion between proteins is not needed 33. Pathways are not linear, in fact the same protein may act in multiple pathways 34. Relay proteins serve as branch points where the signal may go in one of two directions xxiii. Termination of the signal35. Each step in the pathway lasts only a short time, t his makes the proteins arrange for a new signal 36. When the signaling molecule leaves leave the receptor it reverts to its inactive form and the relay molecules follow