Questions: You add a dye that is unable to diffuse across the membranes of lab-grown cells. You then add a ligand to the cells and after five minutes, the dye is found in the cell. What type of receptor did the ligand bind? A. G-protein coupled receptor B. Ligand-gated ion channel C. Receptor tyrosine kinase D. Receptor serine kinase

The answer is B: Ligand-gated ion channel.

Explanation for each option:

A. G-protein coupled receptor: These receptors typically activate intracellular signaling pathways through the production of second messengers, but they do not directly allow substances to pass through the membrane. Therefore, they would not allow the dye to enter the cell.

B. Ligand-gated ion channel: These receptors form a channel that opens in response to the binding of a ligand, allowing ions or other small molecules to pass through the membrane. If the dye is small enough to pass through the channel, this would explain how it enters the cell.

C. Receptor tyrosine kinase: These receptors are involved in signaling pathways that often lead to changes in gene expression or cellular activity, but they do not form channels that allow substances to pass through the membrane.

D. Receptor serine kinase: Similar to receptor tyrosine kinases, these receptors are involved in signaling pathways and do not form channels for substances to pass through the membrane.

In summary, the ligand likely bound to a ligand-gated ion channel, allowing the dye to enter the cell.