Which of the Following Is NOT Generally Characteristic of Pathways

Multiple Choice

Which of the following is NOT generally characteristic of pathways activated by second messengers?

A) Each signaling pathway consists of a series of distinct proteins that operate in sequence.
B) Each protein in the pathway typically acts by altering the conformation of the previous (upstream) protein in the series, an event that activates or inhibits the protein.
C) Alterations in the conformations of signaling proteins are often accomplished by protein kinases and protein phosphatases that, respectively, add or remove phosphate groups from other proteins.
D) Some phosphatases and protein kinases in the pathway have numerous proteins as their substrates; others act on only a single protein substrate or a single amino acid of a protein substrate.
E) Many of the protein substrates of the pathway enzymes are enzymes themselves, like other kinases and phosphatases, but they include ion channels, transcription factors and various regulatory molecules.