Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of substances on opposite sides of the membrane?
a. Intracellular receptor
b. G protein-coupled receptor
c. Phosphorylated receptor tyrosine kinase dimer
d. Ligand-gated ion channel

Verified step by step guidance

1. Understand the function of each type of receptor mentioned in the problem. Intracellular receptors are located inside the cell and typically bind to signaling molecules that can cross the cell membrane, such as steroid hormones. G protein-coupled receptors (GPCRs) are membrane-bound receptors that activate G proteins, which then trigger various intracellular signaling pathways. Receptor tyrosine kinases are membrane receptors that, upon ligand binding, undergo phosphorylation and dimerization, leading to activation of downstream signaling pathways. Ligand-gated ion channels are membrane receptors that open or close in response to ligand binding, allowing ions to pass through the membrane.
2. Focus on the mechanism of ligand-gated ion channels. These receptors are directly involved in changing the distribution of ions across the cell membrane. When a signaling molecule binds to a ligand-gated ion channel, it causes the channel to open or close, allowing specific ions to move across the membrane.
3. Consider the directness of the effect. Ligand-gated ion channels have an immediate impact on the membrane's ion distribution because they physically open or close to allow ions to pass through, altering the concentration gradient across the membrane.
4. Compare this mechanism to the other receptors. Intracellular receptors, GPCRs, and receptor tyrosine kinases typically initiate a cascade of intracellular events that eventually lead to changes in cell function, but they do not directly alter the distribution of substances across the membrane.
5. Conclude that the receptor type that directly changes the distribution of substances across the membrane is the ligand-gated ion channel, as it allows ions to pass through the membrane upon ligand binding.

Key Concepts

Ligand-Gated Ion Channel

Ligand-gated ion channels are a type of receptor that, upon binding with a signaling molecule (ligand), undergo a conformational change to open or close an ion channel. This directly alters the distribution of ions across the cell membrane, affecting cellular activity. These channels are crucial in processes like neurotransmission, where rapid changes in ion flow are necessary.

Membrane Transport

Membrane transport refers to the movement of substances across the cell membrane, which can be passive or active. In the context of ligand-gated ion channels, the transport is typically passive, allowing ions to flow down their concentration gradient. This movement is essential for maintaining cellular homeostasis and facilitating signal transduction.

Signal Transduction

Signal transduction is the process by which a cell responds to external signals, often involving receptors that initiate a cascade of intracellular events. Ligand-gated ion channels play a direct role in signal transduction by altering ion distribution, which can lead to changes in cell function, such as muscle contraction or neuronal firing.