The cell membrane is semi-permeable. It allows some molecules to enter easily inside the cell whereas some molecules are blocked from entering the cell.
Small, polar molecules and hydrophobic molecules enter easily through the cell membrane. But large molecules and ions cannot easily move inside the cell membrane.
A hydrophilic substance like the substance L mentioned in the question enters the cell membrane through the help of carrier proteins. The substance attached to the large protein might enter through active or passive diffusion but it can only enter the cell by attaching to carrier proteins.
Examples of membrane receptors:Ligand, located outside the cell Ligands are connected to specific receptor proteins based on the shape of the active site of the protein. The receptor releases the second messenger after the ligand is connected to the receptor. Further Explanation
In biochemistry and pharmacology, receptors are protein molecules that receive chemical signals from outside the cell.
Receptors can be bound to cell membranes, cytoplasm, or the nucleus, each of which can only be attached by certain types of signaling molecules. Signaling molecules attached to a receptor are called ligands, which can be a peptide or other small molecules such as neurotransmitters, hormones, drugs, or toxins.
Receptor proteins can be classified by their location. Transmembrane receptors include receptors connected with ion channels (ionotropic), receptors connected to protein G (metabotropic), and receptors connected with enzymes.
Not every ligand that binds to the receptor also activates the receptor. The ligand class can be divided into:Agonist (full) Partial agonist Antagonist Inverse agonist Allosteric modulator
Receptors capable of producing biological responses in the absence of bound ligands are said to display "constitutive activity".
Class: Middle School
Keywords: membrane, ligand, receptor
lunar landing mission. apollo 11 was the first manned mission to land on the moon. the first steps by humans on another planetary body were taken by neil armstrong and buzz aldrin on july 20, 1969. the astronauts also returned to earth the first samples from another planetary body.