Signal Transduction Pathways

Signal Transduction Pathways What happens inside of a cell when a signal has been received? Why? When cells release signal molecules (ligands) to send a message, and the message is received, a whole host of events take place inside the cell. The ultimate goal is a response—a gene is turned on, a protein is manufactured, an enzyme is activated, the cell divides or dies, etc. There are many responses that could occur, but the pathways to those responses are very similar. Model 1 – Basic Signal Transduction Pathway Ligand e an br ll Ce m em Cytoplasm Activated relay protein 1 Receptor protein Activated relay protein 2 Response Activated relay protein 2 Response Activated relay protein 2 Response 1. According to Model 1, does the signal transduction pathway occur inside or outside of a cell? It is inside the cell 2. Compare the shape of the ligand in Model 1 to the shape of the receptor protein. They work together and they fit together 3. The four steps in the signal transduction pathway are listed below. Label the diagram above with the Roman numerals to indicate where on the diagram each step is taking place. I. Signaling II. Reception III. Transduction IV. Response 4. Based on the diagram in Model 1 and your labels, propose a definition for “transduction” in the context of the signal transduction pathway. It is the translation that moves the signal into the response 5. Amplification often occurs during the transduction step in the signal transduction pathway. a. Define “amplification” as it is used in everyday language. Making something more strong or bigger b. Explain how the signal in Model 1 was amplified. it leads to a threefold response 6. List several possible responses that could occur due to a signal being received by a cell. (Hint: There are several listed in the Why? box.) growth and enzyme activation 7. Once the response is achieved in a cell, what would need to occur to stop the response? to stop the response they would need to slow it down 12. What is the cell’s response to the signal received in Model 2? Transcription factor activates 13. In Model 2, steps 3, 4, and 5 are shown as amplification steps. Describe what that means in terms of this signal transduction pathway example. more molecules than the original ligand 14. What advantage would there be to an organism if the signal transduction pathway had several amplification steps? a low count of the ligand molecule 15. Describe what would occur in the cell if the activated protein kinase enzymes continued to be active for a long period of time. ATP molecules get used up 16. What would need to occur in the cell to deactivate the protein kinase enzymes? Deactivation of relay protein 17. Protein phosphatases are enzymes that remove phosphate groups from proteins. Complete the illustration in Model 2 by adding at least two protein phosphatases (PP) to show how the cell is returned to inactive status. 18. Although signal transduction pathways vary among species, there are several common elements. Explain how a biologist might use details about signal transduction pathways used in different species as evidence for evolutionary relatedness. species with common signal pathways are closely related Extension Questions Model 3 – Secondary Messengers 1 Transport protein ane Cell membr Active relay protein Cytoplasm 2 3 Secondary messenger 4 Response 5 Active relay protein 19. Consider the signal transduction pathway in Model 3. What event begins the process of producing a cellular response? ligand binds to receptor protein 20. Locate the secondary messenger molecules in Model 3. a. Describe the type of diffusion that is used to get the secondary messengers into the cell. facilitated diffusion b. What activates or opens the transport protein channel that allows the secondary messengers to enter the cell? active relay protein