Question

Fill in the blanks: A protein hormone binding to its extracellular receptor is acting as a ________ messenger, whereas the intracellular effects must be mediated by a ________ messenger.

(A) First, Second
(B) Primary, Secondary
(C) Second, First
(D) Secondary, Primary

Answer 1

The correct completion for the sentence is 'first messenger' for the extracellular binding hormone and 'second messenger' for the mediator of intracellular effects, making the answer (A) First, Second.

Step-by-step explanation:

Fill in the blanks: A protein hormone binding to its extracellular receptor is acting as a first messenger, whereas the intracellular effects must be mediated by a second messenger.

The correct answer is (A) First, Second.

When lipid insoluble hormones bind to receptors on the plasma membrane surface, they trigger a signaling pathway to change the cell's activities. The hormone is called a first messenger and upon binding to the receptor, the associated G-protein activates a second messenger like cyclic AMP (cAMP), which then triggers a cellular response.