Question

Given below are two statements:
Statement (I) : A specific receptor is present in the plasma membrane.
Statement (II) : Water soluble hormone bind to the specific receptor and generate a second messenger as a consequence of ligand receptor interaction.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement I and Statement II are correct
• B. Both Statement I and Statement II are incorrect
• C. Statement I is correct but Statement II is incorrect
• D. Statement I is incorrect but Statement II is correct

Hint:

To remember hormone receptor locations:
- Water-soluble (peptides, proteins) \(\rightarrow\) cannot cross membrane \(\rightarrow\) Plasma membrane receptors (uses second messengers).
- Lipid-soluble (steroids, thyroid hormones) \(\rightarrow\) crosses membrane easily \(\rightarrow\) Intracellular/Nuclear receptors (direct gene transcription).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Hormones act as biochemical signals that regulate cellular physiology by binding to specific target cell receptors.
The cellular location of these receptors depends entirely on the chemical nature (solubility) of the hormone.

Step 2: Detailed Explanation:
Let us evaluate the two statements:
- Statement (I) is correct:
Cells express specific receptors on their plasma membrane to recognize and bind extracellular signaling molecules (ligands).
These membrane receptors are typically transmembrane proteins spanning the lipid bilayer.
- Statement (II) is correct:
Water-soluble hormones, such as peptide hormones (e.g., insulin, glucagon) and catecholamines (e.g., epinephrine), are highly hydrophilic.
Because they are hydrophilic, they cannot freely cross the hydrophobic core of the plasma membrane's lipid bilayer.
Instead, they must bind to specific receptors located on the extracellular face of the plasma membrane.
The binding of the hormone (ligand) to the receptor triggers a conformational change that initiates intracellular signaling cascades.
This activation stimulates the generation of intracellular second messengers, such as cyclic adenosine monophosphate (cAMP), inositol trisphosphate (\(\text{IP}_3\)), or diacylglycerol (DAG).
These second messengers amplify the signal inside the cell to mediate the hormone's physiological effects.
Thus, both statements are scientifically accurate and describe the classic mechanism of action of hydrophilic hormones.

Step 3: Final Answer:
Both Statement I and Statement II are correct.