question: Which statement is false? A. The lifetime of an intracellular signalin
ID: 204992 • Letter: Q
Question
question: Which statement is false?
A. The lifetime of an intracellular signaling molecule must be short for the cell to be able to cause a change in the concentration of the signaling molecule in an efficient manner.
B. PKA is more closely related to PKC than to PKG at the amino acid level.
C. Components of intracellular signaling pathways can be small molecules, proteins or lipids.
D. Second messengers can convey a signal via a change in their steady state level.
E. Negative feedback systems play important roles in regulating cellular signaling.
2.Which statement best explains how different proteins with SH2 domains bind to their respective targets?
(1 point)
A. Some SH2 domains bind to phospho-tyrosines while others do not.
B. The specificity of the interaction is controlled by a combination of the amino acids surrounding the phosphotyrosine plus the amino acids surrounding the SH2 domain.
C. A conformational change in the SH2 domain confers the specificity of the interaction. (This might be it)
D. The presence of more than one phosphotyrosine confers specificity of binding of different SH2 domains.
Explanation / Answer
Q1
Statement B is false.
PKA is more related to PKG than PKC. This can be explained on the basis of the fact that both PKA and PKG have cNMP( nucleoside monophophate) binding domains which allosterically modulate these enzymes. However, it may be noted that the regulatory domain in PKG is part of the same polypeptide i.e PKG has a single polypeptide chain whereas in PKA regulatory domais are present on separate polypeptide chain. PKA consists of two regulatory and two catalytic subunits. PKA is activated by cAMP and PKG is activated by cGMP.
PKC is activated by DAG or Ca or both depending on the isofom.
Q2
A. Option A is incorrect as all SH2 domains bind to phosphotyrosines.
B. Option B is correct and explains how different proteins with SH2 domains bind to their respective targets. This can be explained by the fact that all SH2 domains have a conserved phosphotyrosine pocket (pTyr pocket) which binds to phosphotyrosine residues. The specificity of SH2 domain containing proteins is attributed to the surrounding amino acids of the pTyr pocket. Also the specificity is conferred by the amino acids surrounding the phosphotyrosine residues.
This explains the selectivity by which a given SH2 domain is able to recognize its target protein peptide, even though the common recognition site, i.e., the pTyr pocket, is so highly conserved.
C. Option C is incorrect as conformational change alone can not confer specificity.
D. Again option D is incorrect as it is not necessary to have more than one phosphotyrosine residues for specificity.
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