CPPS 325 FINAL EXAM QUESTIONS WITH CORRECT ANSWERS 2023/2024 Graded A+

CPPS 325 FINAL EXAM QUESTIONS WITH CORRECT ANSWERS 2023/2024 Graded A+. What is the only example of conformational change activation? - Correct Answer-Insulin receptor kinase. All other RTKs are activated through forms of dimerization. What are the two forms of dimerization? - Correct Answer-i) Receptors exist as unactivated dimers until ligand binds (Twist theory) ii) exist as monomers that are brought together and activated by ligand binding. What is the most common method of dimerization activation? - Correct AnswerReceptors existing as monomers. What is the Twist Theory? - Correct Answer-RTKs exist as formed dimers and when a ligand binds the dimer undergoes a twist/shift in shape so the catalytic domains can become fully active and therefore allow for autophosphorylation in key tyrosine residues outside the catalytic domain. What is the monomer dimerization activation pathway? - Correct Answer-The monomers need to dimerize to fully activate the TK/SH1 domains. Ligand must bind external domains of two monomer RTKs so they dimerize. This results in increased enzymatic activity of the IC catalytic SH1/TK domains by phosphorylating key tyrosine residues outside the catalytic domain. Transphosphorylation of tyrosines occurs so the kinase activation can occur, and transphosphorylation of regions that create the docking site. The phosphorylated tyrosine residues serve as docking sites for cytoplasmic signalling molecules. What does RTK activation require? - Correct Answer-Dimerization and transphosphorylation!! Where are tyrosines phosphorylated - Correct Answer-They are first phosphorylated within the kinase/catalytic domains to increase the activity of enzyme and this triggers phosphorylation outside the catalytic/kinase domain that produces a docking site. What does phosphorylation of tyrosines within the kinase/catalytic domain do? - Correct Answer-Increases the kinase activity of the enzyme. What does phosphorylation of tyrosines outside the kinase/catalytic domain do? - Correct Answer-It creates high-affinity binding sites for a number of IC signalling properties. What are some IC signalling proteins that bind to the docking sites created by phosphorylation outside the kinase/catalytic domain? - Correct Answer-- PLC (amplifiers) which leads to release of Ca2+ -SRC TK (non-receptor TK) -Adaptor proteins like Grb-2. (activation of Grb-2 leads to recruitment of SOS and activation of Ras) What is Ras? - Correct Answer-A small monomeric G-protein anchored to the inner PM involved in many signalling responses when activated to trimeric G-protein. What is Ras regulate by? - Correct Answer-Ras is regulated by guanine nucleotide exchange factor (GEF) and GTPase activating proteins (GAPs). Ras switches between active and inactive states. Ras G protein inactive bound to GDP. GDP is exchanged for GTP by GEFs and Ras is activated. GAPs accelerate OFF by enhancing the hydrolysis of GTP to GDP. What happens when Ras proteins are mutated? - Correct Answer-Mutated Ras proteins are unable to dissociate GTP, so they are stuck in the ON or proliferative state. Can lead to cancer. What happens when Ras-GAPs when they are mutated? - Correct Answer-Mutations lead to disease because the Ras-GAPs proteins can't hydrolyze GTP back to GDP efficiently so Ras stays activated longer than it should. What is SOS? - Correct Answer-Is a guanine nucleotide exchange factor. How is Ras linked RTKs? - Correct Answer-An adaptor protein (Grb-2) and a GEF (SOS) link activated RTKs to Ras (downstrea signalling proteins). What is Grb-2? - Correct Answer-Grb-2 is a adaptor (linker) protein that couples activated RTKs to downstream signalling proteins like Ras. What is Grb-2 composed of ? - Correct Answer-Composed of SH2 and SH3 domains. What is the function of SH2 domain of Grb-2? - Correct Answer-SH2 (Src-homology 2) domain of Gr-2 binds to specific phosphotyrosines on activated RTK. Mediates activity. What is the function of SH3 domain of Grb-2? - Correct Answer-SH3 is involved in protein interaction and binds to proline rich regions of SOS. SOS is a GEF so it regulates Ras activity. How are RTKs linked to G-proteins? - Correct Answer-RTKs are activated and then they are coupled to downstream signalling proteins such as Ras (G-protein). RTK signalling activates G-protein signalling. RTK activation leads to association with SH2 domain of the linker Grb-2 protein. and the SH3 domain links with SOS that is a GEF that exchanges GDP for GTP on Ras. How are Ras and RTK different? - Correct Answer-Ras is a G-protein that is activated through RTK signalling. What is the linkage pathway between RTK and G-protein Ras? - Correct Answer-RTK- (SH2-SH3)-SOS-Ras-Raf (SH2-SH3) domains constitute the Grb-2 linkage protein. SH3 domain binding to the proline-rich region of SOS brings the GEF from the cytosol to the membrane. The Grb-2 linker protein does not actually link with the signalling protein, but the exchange factor that activates the G-protein. What is Raf? - Correct Answer-Is a MAPKKK. Ras-Associating Factor. Serine/threonine kinase What is the activation of Raf associated with? - Correct Answer-Activation is associated with several proteins: - serine/threonine phosphatase P2A - Hsp90 chaperone heat shock protein - Scaffold protein 14-3-3 What is the Hsp90 function in activation of Raf? - Correct Answer-Is a chaperone heat shock protein. It helps to stabilize Raf and is involved in proper cell localization. What is the scaffold protein 14-3-3 function in Raf activation? - Correct Answer-Is a phosphoserine adaptor/chaperone protein. It locks Raf in its inactive formation. It interacts with the RBD N-terminal region bound at two phosphoserine residues on Raf to inhibit Raf activation. 14-3-3 is autoinhibitory. What is an essential feature of Raf? - Correct Answer-The N-terminal region hinders the activity of the catalytic domain of Raf. There are a number of modifications that need to occur in order to remove the restraint on Raf to enable its activation. Scaffold protein 14-3-3 interacts with the N-terminal region to lock Raf in the inactive form.