Signaling molecules, or ligands, can be classified as either hydrophilic, meaning they are inclined to remain in water, or hydrophobic, indicating a tendency to repel water.
Hydrophilic Signaling Molecules:
Hydrophilic signaling molecules, which constitute the majority, are able to float into the extracellular space without restriction, facilitating their movement toward target cells. When it comes to cell surface receptors, the ligand that binds to them needs to possess certain characteristics, primarily being hydrophilic. This is because the cell’s plasma membrane is hydrophobic, which prevents the hydrophilic ligands from crossing it and entering the cell’s interior. Therefore, to transmit information effectively, these ligands must bind to the cell surface receptor (CSR).
Hydrophobic Signaling Molecules:
Hydrophobic signaling molecules are unable to move freely through the extracellular environment. Therefore, they rely on carrier proteins for transport to target cells. Once delivered, these hydrophobic molecules are capable of passing through the cell membrane, where they interact with receptor proteins situated in either the cytoplasm or nucleus.
