Answer
Peptide hormones need a second messenger system because peptide hormones cannot pass through the plasma membrane of the target cell. Thus, they bind to protein receptor outside the cell that alerts second messenger molecule inside the cell which activates the enzymes.
Work Step by Step
Peptide hormones need a second messenger system because peptide hormones cannot pass through the plasma membrane of the target cell. Thus, they bind to protein receptor outside the cell that alerts second messenger molecule inside the cell which activates the enzymes.
