Nuclear Receptors and Gene Regulation — MCQs
Which set of hormones exclusively utilizes nuclear receptors?
All of the following statements about HRT (hormone replacement therapy) are true except:
A patient on tamoxifen therapy is most likely to develop which of the following?
Which of the following hormones does not mediate its action through cAMP?
Steroid hormone receptors have attachment site for all except:
Which of the following hormones will be affected most after the change in sex hormone binding globulin?
What is Reifenstein syndrome?
Which of the following acts via the steroid-thyroid receptor superfamily (nuclear receptors)?
Which of the following actions is NOT associated with tricyclic antidepressants?
Which of the following binds to intracellular receptors?
Nuclear Receptors and Gene Regulation Indian Medical PG Practice Questions and MCQs
Question 1: Which set of hormones exclusively utilizes nuclear receptors?
- A. Estrogen, Thyroxine, Insulin
- B. Cortisol, Aldosterone, TSH
- C. Progesterone, Testosterone, Glucagon
- D. Vitamin D, Retinoic acid, Progesterone (Correct Answer)
Explanation: ***Vitamin D, Retinoic acid, Progesterone*** - **Vitamin D**, **retinoic acid**, and **progesterone** are all **lipid-soluble molecules** that can readily cross the cell membrane and bind to **intracellular nuclear receptors**. - Their binding to nuclear receptors directly influences **gene transcription** and protein synthesis. *Estrogen, Thyroxine, Insulin* - While **estrogen** and **thyroxine** utilize nuclear receptors, **insulin** is a peptide hormone that binds to **cell surface receptors**. - **Insulin** activates a signal transduction cascade, rather than directly influencing gene transcription via nuclear receptors. *Cortisol, Aldosterone, TSH* - **Cortisol** and **aldosterone** are steroid hormones that bind to nuclear receptors. - However, **TSH (Thyroid Stimulating Hormone)** is a peptide hormone that binds to **G protein-coupled receptors** on the cell surface of thyroid cells. *Progesterone, Testosterone, Glucagon* - **Progesterone** and **testosterone** are steroid hormones that utilize nuclear receptors. - **Glucagon** is a peptide hormone that binds to **G protein-coupled receptors** on the cell surface of target cells, primarily hepatocytes.
Question 2: All of the following statements about HRT (hormone replacement therapy) are true except:
- A. It increases the risk of coronary artery disease
- B. It increases bone mineral density
- C. It increases the risk of breast cancer
- D. It increases the risk of endometrial cancer (Correct Answer)
Explanation: ***It increases the risk of endometrial cancer*** - This statement is only true for **unopposed estrogen** therapy in women with an intact uterus; combined HRT (estrogen plus progesterone) significantly **reduces** this risk. - The addition of **progesterone** to estrogen HRT is protective against endometrial hyperplasia and cancer. *It increases the risk of coronary artery disease* - Studies have shown that HRT, particularly when initiated several years after menopause, can **increase the risk of cardiovascular events**, including coronary artery disease. - The **Women's Health Initiative (WHI)** study highlighted these risks, especially in older women starting HRT. *It increases bone mineral density* - Estrogen is crucial for maintaining bone density, and HRT can **slow down bone loss** and **reduce the risk of osteoporosis and fractures** in postmenopausal women. - This is a well-established benefit of HRT for bone health. *It increases the risk of breast cancer* - Combined estrogen-progestin HRT has been consistently shown to **increase the risk of breast cancer**, especially with prolonged use (more than 3-5 years). - This increased risk is a significant concern when considering HRT.
Question 3: A patient on tamoxifen therapy is most likely to develop which of the following?
- A. Increased risk of breast cancer
- B. Increased LDL cholesterol levels
- C. Endometrial hyperplasia (Correct Answer)
- D. Increased risk of myocardial infarction
Explanation: ***Endometrial hyperplasia*** - Tamoxifen acts as an **estrogen receptor agonist** in the uterus, stimulating endometrial proliferation and increasing the risk of hyperplasia, polyps, and endometrial cancer. - This effect is particularly seen in **postmenopausal women** and is a major concern with long-term use. *Increased risk of breast cancer* - Tamoxifen is primarily used to **reduce the risk of breast cancer recurrence** and as a chemopreventive agent in high-risk individuals. - It acts as an **estrogen receptor antagonist** in breast tissue, blocking estrogen's proliferative effects. *Increased LDL cholesterol levels* - Tamoxifen typically has a favorable effect on lipids, often causing a **decrease in total and LDL cholesterol** levels. - This effect is due to its estrogenic activity in the liver. *Increased risk of myocardial infarction* - While tamoxifen can increase the risk of **thromboembolic events** (e.g., DVT, pulmonary embolism), it generally does not increase, and may even decrease, the risk of myocardial infarction due to its beneficial effects on lipid profiles. - Its overall cardiovascular risk profile is complex, but MI is not a commonly cited side effect.
Question 4: Which of the following hormones does not mediate its action through cAMP?
- A. Glucagon
- B. Follicle stimulating hormone
- C. Estrogen (Correct Answer)
- D. Luteinizing hormone
Explanation: ***Estrogen*** - **Estrogen** is a **steroid hormone** that mediates its action by binding to intracellular receptors, forming a complex that directly influences gene transcription. - Steroid hormones, due to their **lipophilicity**, can cross the cell membrane and do not typically rely on cell surface receptors or second messengers like cAMP. *Glucagon* - **Glucagon** acts on a **G protein-coupled receptor (GPCR)**, specifically a Gs-coupled receptor, leading to the activation of adenylyl cyclase. - This activation increases the intracellular concentration of **cAMP**, which then activates protein kinase A to mediate its effects, primarily on glucose metabolism. *Follicle stimulating hormone* - **FSH** binds to a **GPCR** on target cells, activating the Gs protein pathway. - This activation stimulates **adenylyl cyclase** and increases intracellular **cAMP** levels, which are critical for its role in gamete development. *Luteinizing hormone* - **LH**, like FSH, binds to a cell surface **GPCR** that activates the Gs protein. - This leads to the stimulation of **adenylyl cyclase** and an increase in **cAMP**, mediating its effects on steroidogenesis and ovulation.
Question 5: Steroid hormone receptors have attachment site for all except:
- A. Hormone responsive element
- B. Steroid hormone
- C. Transcription activators (Correct Answer)
- D. Transcription repressors
Explanation: ***Transcription activators*** - **Steroid hormone receptors** bind directly to **steroid hormones** and **hormone response elements (HREs)** on DNA, as well as to **transcription repressors** in their inactive state. - They do not have a direct attachment site for **transcription activators**; rather, activated steroid receptors can *act* as transcription activators or co-activators through protein-protein interactions. *Hormone responsive element* - This is a specific **DNA sequence** in the promoter region of target genes where the **steroid hormone-receptor complex** binds to regulate gene transcription. - It defines the genomic target for the activated steroid receptor, ensuring **gene-specific responses**. *Steroid hormone* - The **steroid hormone** itself binds to its specific receptor, inducing a conformational change that allows the receptor to translocate to the nucleus and bind to DNA. - This binding is essential for the **receptor's activation** and subsequent gene regulation. *Transcription repressors* - In the absence of a steroid hormone, **transcription repressors** (e.g., heat shock proteins) are often bound to the **steroid hormone receptor**, preventing its activation and binding to DNA. - Upon hormone binding, these repressors dissociate, allowing the receptor to become active and modulate **gene expression**.
Question 6: Which of the following hormones will be affected most after the change in sex hormone binding globulin?
- A. Testosterone (Correct Answer)
- B. Progesterone
- C. DHEA
- D. Estrogen
Explanation: ***Testosterone*** - **Sex hormone-binding globulin (SHBG)** binds primarily to **testosterone** (and dihydrotestosterone) with **high affinity**. - SHBG has approximately **5 times greater affinity** for testosterone compared to estradiol. - A change in SHBG levels will significantly impact the proportion of **free (biologically active) testosterone** available in the circulation, thus affecting its overall function and measurement. - This makes testosterone the hormone **most affected** by changes in SHBG levels. *Progesterone* - **Progesterone** is primarily bound to **albumin** and **corticosteroid-binding globulin (CBG)**, not SHBG. - Therefore, changes in SHBG would have minimal direct impact on progesterone levels or its bioavailability. *DHEA* - **Dehydroepiandrosterone (DHEA)** is mostly bound to **albumin** in the blood. - Its binding to SHBG is negligible, making changes in SHBG irrelevant to its overall circulating levels or activity. *Estrogen* - **Estrogen (estradiol)** also binds to SHBG, but with **significantly lower affinity** than testosterone (approximately 5-fold less). - While affected by SHBG changes, the impact is less pronounced than on testosterone due to the lower binding affinity and its additional binding to albumin.
Question 7: What is Reifenstein syndrome?
- A. Partial androgen insensitivity syndrome due to receptor mutation. (Correct Answer)
- B. Complete androgen insensitivity syndrome with female external genitalia
- C. 5-alpha reductase deficiency causing ambiguous genitalia
- D. Gonadal dysgenesis with streak gonads
Explanation: Partial androgen insensitivity syndrome due to receptor mutation. - **Reifenstein syndrome** is a form of **partial androgen insensitivity syndrome (PAIS)**, characterized by varying degrees of undervirilization in 46,XY individuals. [4] - It results from mutations in the **androgen receptor (AR) gene**, leading to impaired androgen signaling. [4] *Complete androgen insensitivity syndrome with female external genitalia* - This describes **complete androgen insensitivity syndrome (CAIS)**, where affected individuals are 46,XY with completely female external genitalia, normal breast development, but no uterus. [4] - Unlike Reifenstein syndrome, there are no signs of virilization. [4] *5-alpha reductase deficiency causing ambiguous genitalia* - **5-alpha reductase deficiency** impedes the conversion of testosterone to the more potent **dihydrotestosterone (DHT)**, which is crucial for external male genital development. - While it causes **ambiguous genitalia**, it's a defect in hormone metabolism, not the androgen receptor itself. *Gonadal dysgenesis with streak gonads* - **Gonadal dysgenesis** refers to conditions where the gonads (testes or ovaries) fail to develop or develop abnormally, often leading to **streak gonads**. [3] - This is a primary gonadal developmental defect, distinct from disorders of androgen action or synthesis. [1], [2]
Question 8: Which of the following acts via the steroid-thyroid receptor superfamily (nuclear receptors)?
- A. GH
- B. Enkephalins
- C. Insulin
- D. Vitamin D3 (Correct Answer)
Explanation: ***Vitamin D3*** - **Vitamin D3** (calcitriol) is a **steroid hormone** that acts by binding to the **vitamin D receptor (VDR)**, which is a member of the **steroid-thyroid receptor superfamily** of nuclear receptors. - This binding leads to gene transcription modulation, affecting calcium and phosphate homeostasis. *GH* - **Growth Hormone (GH)** acts primarily through **tyrosine kinase-associated receptors** (specifically, the JAK/STAT pathway), not nuclear receptors. - It's a **peptide hormone** that regulates growth, metabolism, and body composition. *Enkephalins* - **Enkephalins** are **opioid peptides** that bind to **G protein-coupled receptors (GPCRs)** on the cell surface. - They are involved in pain modulation and do not act via nuclear receptors. *Insulin* - **Insulin** is a **peptide hormone** that primarily acts via **receptor tyrosine kinases (RTKs)**, not nuclear receptors. - Upon binding, it initiates a signaling cascade involving phosphorylation events, regulating glucose metabolism.
Question 9: Which of the following actions is NOT associated with tricyclic antidepressants?
- A. Block 5-HT or NE reuptake
- B. Anticholinergic action
- C. MAO inhibition (Correct Answer)
- D. Causes sedation
Explanation: ***MAO inhibition*** - Tricyclic antidepressants (TCAs) primarily exert their effects by inhibiting the reuptake of **norepinephrine** and **serotonin**, not by inhibiting monoamine oxidase (MAO). - **MAO inhibitors** are a distinct class of antidepressants with a different mechanism of action and side effect profile. *Anticholinergic action* - Many TCAs have significant **anticholinergic effects**, blocking muscarinic receptors and leading to side effects like dry mouth, constipation, and blurred vision. - These effects contribute to the **adverse event profile** of TCAs, especially in elderly patients. *Block 5-HT or NE reuptake* - The primary mechanism of action of TCAs involves the **inhibition of serotonin (5-HT)** and **norepinephrine (NE) reuptake** into presynaptic neurons. - This action increases the concentration of these neurotransmitters in the **synaptic cleft**, thereby potentiating their effects. *Causes sedation* - TCAs frequently cause **sedation**, particularly the more histaminergic ones (e.g., amitriptyline, doxepin), due to their **histamine H1 receptor antagonism**. - This side effect can be beneficial for patients with insomnia but can be problematic for daytime functioning.
Question 10: Which of the following binds to intracellular receptors?
- A. Growth hormone
- B. Vitamin E
- C. Estrogen (Correct Answer)
- D. Insulin
Explanation: ***Estrogen*** - **Estrogen** is a **steroid hormone** that, due to its **lipophilic nature**, can easily pass through the cell membrane to bind to **intracellular receptors** in the cytoplasm or nucleus. - This binding leads to the formation of a **hormone-receptor complex** that acts as a transcription factor, regulating **gene expression**. *Growth hormone* - **Growth hormone** is a **peptide hormone** and therefore **hydrophilic**, meaning it cannot freely cross the cell membrane. - It binds to **transmembrane receptors** on the cell surface, initiating intracellular signaling cascades through pathways like the **JAK/STAT pathway**. *Vitamin E* - **Vitamin E** is a **lipid-soluble vitamin** and an important **antioxidant**, but it does not function as a signaling molecule that binds to intracellular receptors to regulate gene expression in the same manner as steroid hormones. - While it diffuses across membranes due to its lipophilicity, its primary role is to protect cell membranes from **oxidative damage**. *Insulin* - **Insulin** is a **protein hormone** that is **hydrophilic** and cannot pass through the cell membrane. - It binds to **tyrosine kinase receptors** on the cell surface, triggering a cascade of intracellular events like the **PI3K/Akt pathway** to regulate glucose metabolism.
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