Thyroxine is a peptide hormone, but its mechanism is different from other peptide hormones. Which of the following statements is true concerning this difference?
A) It is a stimulant of cellular metabolism and targets all cells.
B) It does not require a second messenger to cause a response.
C) It causes positive feedback.
D) It is very specific in the cell type it targets.

Question

Quizplus · Accepted Answer

Most peptide hormones require a second messenger, such as cAMP or calcium, to cause a response in target cells. Thyroxine, on the other hand, can enter the cell and bind directly to nuclear receptors, without the need for a second messenger.

Thyroxine Is a Peptide Hormone, but Its Mechanism Is Different