Problem 113 - Objective Biology for NEET

Question

Find out the correct statement from the following: 1) Hormones interact with membrane bound receptors normally do not enter the target cells. 2) Iodothyronines have membrane bound receptors. 3) Hormones which interact with intracellular receptors mostly regulate gene expression. 4) Steroid hormones generate second messengers. (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 2 and 4 only

Step-by-Step Solution

Answer

The correct pair of statements, among the given options, is 1 and 3 only, i.e., option (c).

Step 1: Analyze Sentence 1

The first sentence states that hormones which interact with membrane bound receptors do not usually enter their target cells. This is indeed correct, as hormones like these typically attach to a receptor located on the outside of a target cell, sparking a signal within the cell without the hormone itself entering it. Therefore, sentence 1 is correct.

Step 2: Analyze Sentence 2

The second sentence claims that iodothyronines have membrane bound receptors. Iodothyronines, including hormones like T3 and T4, actually interact with intracellular receptors and not membrane bound receptors. They enter the cell and interact directly with the intracellular receptor, thereby influencing gene expression. Therefore, statement 2 is incorrect.

Step 3: Analyze Sentence 3

The third sentence says that hormones which interact with intracellular receptors mostly regulate gene expression. As mentioned previously with the iodothyronines, hormones that interact with intracellular receptors do indeed mostly regulate gene expression; they bind with the receptor and this hormone-receptor complex then influences the cell's DNA. Therefore, sentence 3 is correct.

Step 4: Analyze Sentence 4

The fourth sentence asserts that steroid hormones generate second messengers. This is not completely correct, as steroid hormones usually enter target cells and bind to intracellular receptors, influencing gene expression directly, rather than producing second messengers. Therefore, statement 4 is incorrect.

Step 5: Finding the Correct Statements

Based on the analysis of the statements, Sentence 1 and 3 are correct. Therefore, the answer is the option (c) that contains both 1 and 3.

Key Concepts

Membrane Bound Receptors

Hormones often communicate with our body's cells in fascinating ways. One such way involves membrane bound receptors. These receptors reside on the surface of cells and play a crucial role in signaling without needing the hormone to actually enter the cell. This type of interaction is typical for many hormones, such as protein and peptide hormones.

When a hormone binds to these receptors, it triggers a cascade of reactions inside the cell. This series of events is sometimes referred to as signal transduction. It's like the receptor picks up the phone to relay the message inside without the caller stepping into the room. This process can activate enzymes, open ion channels, or even influence gene expression indirectly.

• The hormone binds to the receptor outside the cell.
• The receptor activates internal signaling pathways.
• Cell responds without the hormone entering.

For example, insulin, a hormone that regulates glucose, uses membrane bound receptors to convey messages efficiently.

Intracellular Receptors

Unlike their membrane-bound counterparts, intracellular receptors are located inside the cell. Hormones like steroid hormones, thyroid hormones (iodothyronines like T3 and T4), and vitamin D often utilize these receptors.

These hormones are typically lipid-soluble, allowing them to pass through the cell's membrane and reach receptor sites within the cell's cytoplasm or nucleus. This feature is crucial, as it enables these hormones to directly influence the cell's function by interacting with its DNA.

• Hormones are lipid-soluble, allowing them to enter the cell easily.
• The hormone-receptor complex forms within the cell.
• Direct interaction with DNA allows precise control over cellular functions.

This direct influence on genetic material means these hormones play a vital role in regulating numerous bodily processes, including metabolism and growth.

Gene Expression

Gene expression is the process through which information from a gene is used to synthesize a functional gene product, usually proteins. Many hormones, particularly those using intracellular receptors, play a pivotal role in controlling gene expression.

When a hormone binds to its intracellular receptor, this complex often becomes an active transcription factor. It then binds to specific DNA sequences, initiating or enhancing the transcription of certain genes. This process ensures that the cell produces the proteins needed for a desired response, such as growth, metabolism, or even cellular repair.

• Hormone-receptor complex acts as a transcription factor.
• Binds to DNA at specific sites to regulate transcription.
• Influences protein production necessary for cellular functions.

This precise mechanism is vital for maintaining homeostasis in the body and ensuring cells perform their roles efficiently.