#Question id: 1257
#Unit 4. Cell Communication and Cell Signaling
Following statements are regarding to protein kinase A which phosphorylates multiple intracellular target proteins expressed in different cell types.
A. Inactive PKA is a tetramer consisting of two regulatory (R) subunits and two catalytic (C) subunits.
B. Each R subunit contains a pseudo-substrate domain whose sequence resembles that of a peptide substrate and binds to the active site in the catalytic domain but is not phosphorylated; thus the pseudo-substrate domain inhibits the activity of the catalytic subunits.
C. active PKA is turned off by binding of cAMP Each R subunit has two distinct cAMP-binding sites, called CNB-A and CNB-B.
D. Binding of cAMP by an R subunit of PKA occurs in a cooperative fashion; that is, binding of the first cAMP molecule to CNB-B increases the Kd for binding of the second cAMP to CNB-A. Thus small changes in the level of cytosolic cAMP can cause proportionately large changes in the number of dissociated C subunits and, hence, in cellular kinase activity.
Which of the following statements are incorrect?
#Question id: 1258
#Unit 4. Cell Communication and Cell Signaling
Following statements are regarding to the desensitization mechanism of GPCR.
A. Several residues in the cytosolic domain of the β-adrenergic receptor are phosphorylated by the enzyme rhodopsin kinase.
B. β-Arrestin binds to specific phosphorylated tyrosine residues in the C-terminal segment of G protein–coupled receptors (GPCRs).
C. Clathrin and AP2, two other proteins bound by β-arrestin, promote endocytosis of the receptor.
D. β-Arrestin also functions in transducing signals from activated receptors by binding to and activating several cytosolic protein kinases like Src activates the MAP kinase pathway, leading to phosphorylation of key transcription factor.
Which of the following combination is incorrect?
#Question id: 1259
#Unit 4. Cell Communication and Cell Signaling
Following statements are regarding to the phosphoinositide pathway.
A. many activated RTKs and cytokine receptors initiate phosphoinositide pathway by recruiting the enzyme phosphatidylinositol-3 kinase (PI-3 kinase) to the membrane.
B. PI-3 kinase adds a phosphate to the 3′ carbon in one of two separate phosphatidylinositol substrates, leading to formation of two phosphatidylinositol 3-phosphates: PI(3,4)P2 or I(3,4,5)P3
C. PI-3 kinase pathway can trigger cell division and prevent apoptosis, thus ensuring cell survival by the activation of PKB.
D. Activated PKB phosphorylates FOXO3a, which induces the expression of several antiapoptotic genes.
Which of the following combination is correct?
#Question id: 1260
#Unit 4. Cell Communication and Cell Signaling
Which of the following statement regarding RTK/Ras pathway is incorrect?
#Question id: 1261
#Unit 4. Cell Communication and Cell Signaling
A FOXO3a mutant in which the three serine residues that are targets for PKB are mutated to alanine then what will be the result?
#Question id: 1262
#Unit 4. Cell Communication and Cell Signaling
Although MAP kinase is often activated in multicellular animals by RTKs or cytokine receptors, signaling from other receptors can activate MAP kinase in other eukaryotic cells. we consider the mating pathway in the yeast S. cerevisiae, a well-studied example of a MAP kinase cascade linked to G protein–coupled receptors (GPCRs). Which of the following statement is incorrect?