Question

Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor on target cells is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine. Which statements are true about the binding of histamine to the histamine H1 receptor? Select all that apply. Histamine diffuses across the plasma membrane to bind to the H1 receptor. Histamine binds extracellularly to the H1 receptor. When histamine binds to the H1 receptor, the receptor undergoes a conformation change and binds the inactive G protein. Histamine binds intracellularly to the inactive G protein, activating the G protein. Once the G protein is active, it binds to the enzyme phospholipase C, activating it. Histamine is likely hydrophilic.

Answer 1

Answer:

-Histamine binds extracellularly to the H1 receptor.

-When histamine binds to the H1 receptor. the receptor undergoes a conformation change and binds the inactive G protein.

-Once the G protein is active, it binds to the enzyme phospholipase C, activating it.

-Histamine is likely hydrophilic.

When histamine encounters a target cell, it binds extracellularly to the H1 receptor, causing a change in the shape of the receptor. This change in shape allows the G protein to bind to the H1 receptor, causing a GTP molecule to displace a GDP molecule and activating the G protein. The active G protein dissociates from the H1 receptor and binds to the enzyme phospholipase C, activating it. The active phospholipase C triggers a cellular response. The G protein then functions as a GTPase and hydrolyzes the GTP to GDP. The G protein dissociates from the enzyme and is inactive again and ready for reuse.

Explanation:

Answer 2

The statements 'histamine binds extracellularly to the H1 receptor', 'when histamine binds to the H1 receptor, the receptor undergoes a conformation change and binds the inactive G protein', 'once the G protein is active, it binds to the enzyme phospholipase C, activating it', and 'histamine is likely hydrophilic' are TRUE.

Histamine is a molecule released during inflammatory and allergic responses.

This molecule (histamine) binds to the G-protein coupled histamine (H1) receptor. This binding triggers a conformational change in the three-dimensional (3D) shape of the G-protein coupled H1 receptor.

Subsequently, the heterodimeric G protein is activated by GTP binding. The G-protein–GTP complex then dissociates from the G-protein coupled H1 receptor and interacts with phospholipase C, thereby activating a transduction signaling pathway.

Finally, the G protein accelerates the hydrolysis of GTP to GDP and thus terminates the transduced signal.

In conclusion, the statements 'histamine binds extracellularly to the H1 receptor', 'when histamine binds to the H1 receptor, the receptor undergoes a conformation change and binds the inactive G protein', 'once the G protein is active, it binds to the enzyme phospholipase C, activating it', and 'histamine is likely hydrophilic' are TRUE.

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