Receptors and routes

A hormone binds to its receptor, and the cell responds by a route that depends on the chemical group of the hormone. You will write the share of receptors occupied, the concentration needed for a share, and the route.

The idea. The share of receptors occupied is $\dfrac{H}{K_d + H}$. If the share is $f$, the concentration is $H = \dfrac{f K_d}{1 - f}$. Peptide hormones and amino acid derivatives use a receptor in the membrane. Steroids and iodothyronines use a receptor inside the cell.

Your tasks.

1. Finish occupied. It gives the share, as a number from 0 to 1.
2. Finish needed. It gives the concentration for a share f.
3. Finish route. It gives "membrane" or "inside" for a chemical group.