Page 34 - Cell biology PDG 2024

B) Intracellular receptors
They are receptors located inside the
cell rather than on its cell membrane
The ligands of intracellular receptors
are characterized by being small,
hydrophobic (water-hating)
molecules, since they must be able to
cross the plasma membrane in order
to reach their receptors. For
example, the receptors for
hydrophobic steroid hormones, such
as vitamin D and sex hormones
estradiol (an estrogen) and
testosterone, are intracellular

When a hormone enters a cell it binds to its receptor causing the
receptor to change shape, allowing the receptor-hormone complex to
enter the nucleus and regulating gene transcription
Hormone binding exposes regions of the receptor that have DNA-
binding activity making them able to attach to specific sequences of DNA
that are found next to certain genes in the DNA of the cell, and when the
receptor binds next to these genes, it alters their level of transcription

• Orphan receptors: is a protein that has a similar structure to other
identified receptors but whose ligand has not yet been identified.
If a ligand for an orphan receptor is later discovered, the receptor
is referred to as an "adopted orphan.

• Orphan ligand: a ligand whose cognate receptor has not yet been
identified.

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