Question

A scientist notices that when she adds a small, water soluble molecule to a dish of cells, the cells turn off transcription of a gene. She hypothesizes that the ligand she added binds to a(n) ______ receptor.

a. Intracellular

b. Hormone

c. Enzyme-linked

d. Gated ion channel-linked

Short answer

The correct answer is (c) Enzyme-linked receptors.

Step-by-step solution

Step 1. Introduction

Ligand is a molecule or atom that irreversibly binds to a receiving protein molecule known as a receptor.

Step 2. Intracellular receptors

The ligands of intracellular receptors are small hydrophobic i.e. water-insoluble molecules.

Step 3. Hormone receptors

The ligands of hormone receptors are hormones and they are specific for hormones.

Step 4. Enzyme-linked receptors 

They are transmembrane proteins and extracellular ligands bind to them on the extracellular side and thus allowing the hydrophilic molecules to pass.

Step 5. Gated ion channel-linked receptors 

The ligands binding to gated ion channel linked receptors are specifically ions and not molecules. These ions are usually sodium, magnesium, calcium or hydrogen.