Question

Last guy got it wrong - Thank you.

2. You discover a signal transduction pathway that regulates actin polymerization. SigC is the ligand, which binds to and activates a receptor tyrosine kinase (RTK). Activation of the RTK leads to the activation of the Ras protein, which then activates the protein kinase PK1 that phosphorylates the RingA protein on S34. When SigC plasma membrane phosphorylated, RingA binds EXTRACELLULAR to the gene regulatory SPACE inactive Ras protein activated Ras protein protein, AP1. When RingA is GDP bound to AP1, AP1 can enter CYTOSOL the nucleus and bind to DNA. to activate transcription of the GTP activated RTK ARP2/ARP3 complex, leading to increased actin PK1 polymerization in the cell. A adaptor protein Ras-GEF portion of this signal transduction pathway is RingA diagrammed in the Figure. i You isolate RNA from ER associated ribosomes. Circle the protein(s) below from this signal transduction pathway that are translated on the ER associated ribosomes. (4 points) Ras-GEF RingA receptor tyrosine kinase ARP2 SigC PK1 actin AP1 ARP3 For each of the situations below, indicate whether you predict actin polymerization will increase, decrease, or stay the same compared to normal cells that are grown in the presence of SigC. (2 points each, 12 points total) a) The cell has a constitutively active Ras protein instead of normal Ras b) S34 on RingA is changed to A34, which cannot be phosphorylated c) The SigC binding site on the RTK is changed so it can no longer bind SigC d) A drug is added to cells that binds PK 1 and hyperactivates its kinase function e) The cytoplasmic domain of the RTK is changed so that it cannot be phosphorylated f The cell lacks the gene for the adaptor protein that binds to RTK and Ras-GEF (Question 2 continues on the next page)

Answer 1

2. You discover a signal transduction pathway that regulates actin polymerization. SigC is the ligand, which binds to and activates a receptor tyrosine kinase (RTK). Activation of the RTK leads to the activation of the Ras protein, which then activates the protein kinase PK1 that phosphorylates the RingA protein on S34. When phosphory lated, RingA binds EXTRACELLULAR to the gene regulatory sPACE protein, AP1. When RingA is bound to AP1, AP1 can enter cYTOsOL the nucleus and bind to DNA to activate transcription of the ARP2/ARP3 leading to increased actin polymerization in the cell. A portion of this signal transduction pathway is diagrammed in the Figure SigC plasma membrane inactive Ras protein activated Ras protein GTP GTP complex, activated RTK PK1 adaptor protein Ras-GE RingA i) You isolate RNA from ER associated ribosomes. Circle the protein(s) below from this signal transduction pathway that are translated on the ER associated ribosomes. (4 points) Ras-GEF eceptor tyrosine kinase ARP2 Nuclear proteins are synthesized in the cytoplasm or outer nuclear membrane ig PK1 actin AP1 ARP3 ii) For each of the situations below, indicate whether you predict actin polymerization will increase decrease, or stay the same compared to normal cells that are grown in the presence of SigC. (2 points each, 12 points total) a) The cell has a constitutively active Ras protein instead of normal Ras Increase b) S34 on RingA is changed to A34, which cannot be phosphorylated Decrease c) The SigC binding site on the RTK is changed so it can no longer bind SigC Decrease d) A drug is added to cells that binds PKI and hyperactivates its kinase function Stav the same e) The cytoplasmic domain of the RTK is changed so that it cannot be phosphorylated Decrease f) The cell lacks the gene for the adaptor protein that binds to RTK and Ras-GEF Decrease