Question

Identify A, B and C in the diagrammatic representation of the mechanism of hormone action.

Select the correct option from the following [NEET (Odisha) 2019]
(a) A-Steroid hormone; B-Hormone-receptor complex, C-Protein

(b) A-Protein hormone, $B$-Receptor; C-Cyclic AMP

(c) A-Steroid hormone; B-Receptor, C-Second messenger

(d) A-Protein hormone; B-Cyclic AMP, C-Homone-receptor complex

Answer/Explanation

Ans. (b)
In the given mechanism of hormone action, the labels are
A-Protein hormone
B-Receptor
C-Cyclic AMP
Hormones which interact with membrane bound receptors do not enter the target cell. These bind with membrane proteins (receptors) and generate second messengers which in turn regulate cellular metabolism, e.g. FSH on ovarian cell membrane.

Question

How does steroid hormone influence the cellular activities? [NEET (National) 2019]

(a) Binding to DNA and forming a gene-hormone complex

(b) Activating cyclic AMP located on the cell membrane

(c) Using aquaporin channels as second messenger

(d) Changing the permeability of the cell membrane

Answer/Explanation

Ans. (a)

Steroid hormones are able to bind to DNA and form a gene-hormone complex. These hormones can easily cross the lipid bilayer of the cell and do not require secondary messengers for the same. Steroid hormones bind to intracellular receptors in the nucleus to form hormone receptor complex which in turn interact with the genome.
cAMP pathway, secondary messengers and change in cell membrane permeability is required in case of proteinaceous hormones which cannot pass through lipid bilayer on their own.

Question

According to the accepted concept of hormone action, if receptor molecules are removed from target organs, then the target organ will [CBSE AIPMT 1995]
(a) not respond to the hormone

(b) continue to respond to hormone without any difference

(c) continue to respond to the hormone but in the opposite way

(d) continue to respond to the hormone but will require higher concentration

Answer/Explanation

Ans. (a)

Hormones are released in normal blood circulation but each hormone stimulates only a specific target organ to initiate a specific response. It is because of the presence of specific receptor protein only in the specific target cell. If these receptor molecules are removed from target organs, the organ will not respond to hormone.

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