CPPS EXAM PRACTICE QUESTIONS WITH CORRECT ANSWERS 2023/2024 (Graded)

CPPS EXAM PRACTICE QUESTIONS WITH CORRECT ANSWERS 2023/2024 (Graded). What isSH1 domain characterized by? - Correct Answer-Catalytic domain of a protein, for example the receptor. and it has the kinase activity. It is responsible for phosphorylating tyrosine residues. What is SH2 domain characterized by? - Correct Answer-Binds peptides with consensus (positional information on C-terminal side of the phosphorylated tyrosine). Very specific. Mediates protein-protein interactions in cellular signalling cascades. Very common in proteins outside the src family. What do SH2 and SH3 domains have as a common funciton? - Correct Answer-They mediate protein-protein interactions in cellular signalling cascades. Very common in proteins outside the src family. What is SH3 domain characterized by? - Correct Answer-Interacts with proline-rich peptide targets (minimal consensus). Mediate protien-protein interatctions in the cellular signalling cascade. Very common in proteins outside the src family. What are PTB domains? - Correct Answer-(Phosphotyrosine binding domain) Bind to phosphorylated tyrosine. Functional equivalent of the SH2 domain, except for the positional informational. Is not the C-terminus like SH2, but the N-terminus side of the phosphorylated tyrosine. shc is a PTB protein. What is the normal action that stops signalling for cell division in the src pathway? - Correct Answer-Contact Inhibition Confluency How do PTB and SH2 domains differ? - Correct Answer-SH2 domains binds consensus on the C-terminus. PTB domains binds the N-terminus. They both mediate cellular signalling. What is shc? - Correct Answer-PTB protein that docks at the N-terminus consensus docking site. What activates a RTK? - Correct Answer-Ligand/agonist binding Upon ligand binding the two activation pathways are? - Correct Answer-1. Conformational change 2. Dimerization What happens with conformational change activation? - Correct Answer-A conformational change that is sufficient enough to activate SH1/catalytic domain results in phosphorylation. 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. What is the importance of RBD in Raf activation? - Correct Answer-It is the N-terminal regulatory domain of the Raf protein. The RBD needs to interact with RasGTP to enable activaiton of Raf. Interaction of RBD with RasGTP at the membrane destabilizes Raf interaction with 14-3-3. This allows for PP2A to dephosphorylate Raf phosphoserines (the locks on the inactive state). What is RBD? - Correct Answer-Ras Binding Domain. It is the Raf N-terminal domain of the Raf protein. How is Raf maintained in an inactivate state? - Correct Answer-Scaffold protein 14-3-3 is bound to two phosphoserine in the N terminus on the Raf protein and locks it in the inactive form. What is the function of serine/threonine phosphatase PP2A in the activation of Raf? - Correct Answer-Once RBD has bound RasGTP the interaction between Ras and 14-3-3 destabilizes. PP2A comes and dephosphorylates the phosphoserines on the Ras. Allowing for other phosphorylations on Raf activating it and causing dimerization. How does Raf associate with RasGTP to become activated? - Correct Answer-RBD binds to the activated Ras (RasGTP) and causes the destabilization of the inhibitory protein 14-3-3 which allows the PP2A to dephosphorylate Raf and allow for other phosphorylations on Raf that result in activation and dimerization. How does Ras activation lead to Raf dimerization in the Raf/MEK/ERK pathway? - Correct Answer-Ras forms nanoclusters when activated and promotes Raf dimerization in the Raf/MEK/ERK pathway. Monomeric Raf is autoinhibited in cytosol. RBD domain of Raf binding to Ras is a high affinity interaction and releases autoinhibition. Ras-RBD interaction leads to Raf activation through side-by-side dimerization. What is Raf? - Correct Answer-Raf (Ras-associating factor) is a MAPKKK = Mitogen activated protein kinase-kinase-kinase. It is a serine/threonine kinase.