GPCR
RTKs
Actin/Myosin
Cytoskeleton
Miscellaneous
100
What is the minimum number of hydrophobic amino acids a GPCR protein must have?
7*20=140
7 transmembrane alpha-helical domains. ~20 hydrophobic amino acids each.
100
How are the docking sites on RTK receptor tails inactivated?
By phosphatases which remove phosphates from the RTK. PhosphoTASE → phosphoTAKE.
100
Ca2+ binds to ______ on the sarcomeric actin filaments.
Troponin
100
How are actin filaments oriented (plus ends/minus ends) at the leading edge of a migrating cell?
Plus end toward the leading edge, minus end toward the cell body
100
Signals must be bound to the membrane in _________ cell signaling.
Contact dependent, juxtacrine
200
What is the main purpose of second messengers?
A. Bind nuclear receptor protein
B. Act as transcription factors to upregulate or downregulate transcription
C. Bind an extracellular ligand
D. Amplify extracellular signals
D. Amplify extracellular signals
200
In RTKs, Ras is a GTPase which is responsible for activating downstream effectors. What will most likely occur if Ras can no longer associate with the plasma membrane?
Ras will be activated significantly less since it is no longer localized near the activated Ras GEF.
200
You are imaging cells by live microscopy and notice a cell which is unable to disassemble its actin structures after polymerization. Which protein might be nonfunctional?
Cofilin
200
What motor proteins are associated with intermediate filaments?
There are none. Intermediate filaments are involved in helping cells withstand mechanical stress. Myosin is associated with actin filaments and kinesin (transport toward the plus end) and dyenin (transport to the negative end) are associated with microtubules.
200
How would muscle contraction be affected by a mutated myosin that has decreased binding affinity for ATP?
Muscles would mimic rigor mortis and become unusually stiff. ATP binding facilitates the dissociation of myosin head from the actin filament.
300
Which of the following mutation(s) would lead to decreased signaling in the cell? Explain your answer.
A. Mutation in which the alpha subunit and beta/gamma complex are unable to associate.
B. Mutation in which G alpha protein is unable to hydrolyze GTP
C. Gain of function in RGS.
D. Mutation in which the receptor has increased affinity for the G protein
C. Gain of function in RGS.
RGS is the G-alpha subunit GAP. Thus, an overactive RGS would lead to continued hydrolysis of GTP by G-alpha and subsequent inactivation of the pathway.
300
Let’s suppose you’re studying RTK signaling in a human cell line. This human cell line is homozygous, wildtype and functions normally. You transfect your cells with a plasmid containing a mutation in which the RTK monomer synthesized is a complete loss of function mutation (kinase dead) and can no longer dimerize. How might cell signaling be affected?
Cell signaling will not be affected. The human cell line itself is not mutated and would be expected to produce the normal amount of RTKs and the mutants cannot “subtract” from the number of available wildtype RTKs because they cannot dimerize regardless.
300
How is the T-tubule able to induce Ca2+ release from the sarcoplasmic reticulum?
The voltage gated Ca2+ channel on the T tubule side directly contacts the Ca2+ release channel in the sarcoplasmic reticulum. Thus when the first opens, it induces a conformational change in the second causing it to open as well.
300
What is the purpose of gamma-tubulin ring complexes in the cell? What structure is this analogous to in the polymerization of actin filaments?
Gamma-tuRC serves as the template and nucleation centers for MTs. This eliminates/overcomes the lag phase during elongation. Thus, they are analogous to using nucleators in actin polymerization.
300
Let’s suppose you decide to sequence different types of myosin. Where would you expect to find conserved sequences, the N terminus or the C terminus?
N terminus is conserved and responsible for binding actin and ATP hydrolysis. C terminus is variable, responsible for binding cargo and/or dimerization.
400
Let’s suppose you have a gain of function mutation in GPCR for adrenaline such that it is always in the conformation to associate with the G protein. However, when there is no adrenaline and the GPCR is trans-cytosed, signaling stops and breakdown of glycogen ceases. How might you explain this discrepancy?
While the GPCR is active, it cannot activate the G protein because the G protein is in the plasma membrane bound by covalently attached lipid tail. Thus, when the receptor is endocytosed, it is too far away from the G protein in the plasma membrane to activate it.
400
You are studying RTKs in a cancer cell line. You observe increased phosphorylated MAPK and suspect a protein in the pathway is mutated. You add a Sos inhibitor but still observe increased phosphorylation of MAPK. Which protein might be mutated and what type of mutation might be present?
Gain of function mutation in either MAPKKK or MAPKK.
Could also be gain of function of mutation in Ras although this cannot be determined from this information alone. Unclear if Ras is constantly bound to GDP because it is overactive or if Sos (Ras-GEF) is inhibited.
400
Describe the action of Arp2/3.
Arp2/3 interacts with NPFs and an actin monomer which induce a conformational change in Arp2/3 making it structurally very similar to the plus end of the actin filament. It binds to the “mother filament” and serves as a “seed” to induce branching at a 70 degree angle.
400
What property of actin polymerization allows cells to protrude the leading edge of a migrating cell ? Why don’t cells eventually run out of actin monomers?
Insertion of actin monomers at the plus ends of branched actin structures at the leading edge
Treadmilling / disassembly of actin away from the leading edge
400
You know G proteins are associated with the plasma membrane. However, when you sequence the G-alpha protein, you do not see any hydrophobic amino acids. How might you explain this discrepancy?
G-alpha proteins are anchored to the PM by covalently attached lipid tails.
500
Describe the GPCR pathway when adrenaline binds.
*DAILY DOUBLE* on PPT slide
Adrenaline binds and activates the GPCR which then activates the G-alpha subunit causing a conformational change which leads to the disassociation of the beta/gamma complex. The activation of the G-alpha subunit activates adenylyl cyclase which catalyzes the conversion of ATP to cAMP, a second messenger. cAMP then binds to and activates PKA which then phosphorylates phosphorylase kinase, which phosphorylates glycogen phosphorylase, leading to the breakdown of glycogen and the increase in glucose concentration.
500
Consider a MAPKKK pathway in which there is MAPK, MAPKK and MAPKKK. How would cellular signaling be affected if there were a hypothetical pathway with only two kinases? E.g. Only MAPK and MAPKK exist and are able to be activated. MAPKKK is nonexistent.
The efficiency of cellular functioning will be decreased because there are fewer proteins in between the signal and the effector. This leads to decreased control of gene expression since there are fewer proteins.
500
You decide to facilitate actin filament polymerization by using actin nucleators. Draw a graph, label the axes, phases and write a short annotation describing the graph.
500
Let’s suppose you have isolated a component of the cytoskeleton from a cell. Unfortunately, you are unsure whether these proteins are actin filaments, intermediate filaments or microtubules. You design five experimental conditions in order to identify the protein. Based on the results provided, what type of cytoskeleton component is this protein most likely to be?
+ATP, - GTP: no polymerization
-ATP, + GTP : limited polymerization
- ATP, + “seeds”, + GTP: normal polymerization
+ ATP, + “seeds”, + GTP: normal polymerization
+ ATP, + “seeds”, + non-hydrolyzable GTP: overactive polymerization
Microtubules because they use GTP to polymerize. They do not use ATP so adding ATP has no effect.
500
Explain how the beta subunit is able to associate with the plasma membrane despite not having a lipid tail.
The beta subunit is very closely associated with the gamma subunit which has a lipid tail to anchor it into the PM.