Oxytocin does not pass through the cell membrane but binds to surface receptors, and it does not directly cause gene transcription. Dopamine increases cAMP upon binding to its receptor. Insulin binds to a receptor tyrosine kinase, causing phosphorylation of tyrosine residues. Option C is correct.
The correct answer to the statement regarding oxytocin is that it is unable to pass through receptor cell membranes. Oxytocin is a peptide hormone that typically binds to receptors on the surface of the cell rather than entering the cell directly. It is not chemically similar to estrogen, which is a steroid hormone, and oxytocin does not directly cause gene transcription as it acts via a secondary messenger system.
Regarding dopamine, after dopamine binds to its receptor, you would expect to see an increase in the concentration of cAMP (cyclic adenosine monophosphate). Dopamine binds to a G-protein-linked receptor, which then activates an enzyme called adenylate cyclase that converts ATP to cAMP.
For the hormone insulin, it first binds to the extracellular portion of the receptor tyrosine kinase, which triggers the receptors to dimerize and autophosphorylate, leading to the phosphorylation of tyrosine residues.
In the case of nitric oxide, as a gaseous signaling molecule, it is likely to bind to an intracellular receptor. Gas molecules like nitric oxide can diffuse across cell membranes and thus do not require a surface receptor to exert their effects.
Hence, C. is the correct option.