Yes, that is correct! Cells contain receptor proteins on their surface and within their cytoplasm. These receptors bind to specific chemicals, called ligands, and trigger a series of events within the cell.

Here's a breakdown:

* Receptor proteins are specialized proteins that recognize and bind to specific ligands. These ligands can be hormones, neurotransmitters, drugs, or other signaling molecules.

* Ligands are molecules that bind to receptors and initiate a cellular response.

* Cell signaling is the process by which cells communicate with each other. Receptor proteins play a crucial role in this process by receiving signals from the outside world and transmitting them to the inside of the cell.

Here are some examples of receptor proteins and their ligands:

* Insulin receptor: Binds to insulin, a hormone that regulates blood sugar levels.

* Acetylcholine receptor: Binds to acetylcholine, a neurotransmitter involved in muscle contraction and other functions.

* Estrogen receptor: Binds to estrogen, a hormone that plays a role in sexual development and other processes.

The binding of a ligand to a receptor protein can trigger a variety of cellular responses, including:

* Changes in gene expression: Ligand binding can activate or inhibit the transcription of specific genes.

* Activation of signaling pathways: Ligand binding can trigger a cascade of events that ultimately lead to a specific cellular response.

* Changes in cell shape or movement: Ligand binding can alter the cytoskeleton of a cell, leading to changes in its shape or movement.

Overall, receptor proteins are essential for cellular communication and play a vital role in maintaining the health and function of the body.