Hormone Biochemistry and Signal Transduction (Receptors, Second Messengers, Cascades) MCQs

Biochemistry · 21 free questions with answers & explanations.

1. Insulin exerts its anabolic effects primarily through which intracellular signalling cascade that ultimately activates glycogen synthase and inhibits glycogen synthase kinase-3 (GSK-3)?
2. Cholera toxin causes persistent diarrhoea by covalently modifying the alpha subunit of Gs protein. What is the biochemical mechanism?
3. A patient with pseudohypoparathyroidism type 1A has elevated PTH but hypocalcaemia and hyperphosphataemia. The target organ is unresponsive to PTH because of a mutation in which signalling component?
4. Which steroid hormone–receptor complex exerts its primary genomic effect by binding to hormone response elements (HREs) as a homodimer and regulating gene transcription in the nucleus?
5. The MAP kinase (MAPK/ERK) pathway activated by growth factor receptor tyrosine kinases depends on which GTPase as a molecular switch immediately downstream of adaptor proteins Grb2 and SOS?
6. Insulin binding to its receptor triggers autophosphorylation of tyrosine residues. What is the IMMEDIATE downstream signaling molecule phosphorylated by the activated insulin receptor tyrosine kinase?
7. A patient with pseudohypoparathyroidism type 1a (Albright hereditary osteodystrophy) has elevated PTH but hypocalcemia. What is the biochemical defect?
8. Which second messenger system is activated by glucagon in the liver to stimulate glycogenolysis?
9. A pharmaceutical company is developing a drug that blocks the DAG arm of the IP3/DAG signaling pathway. Which hormone's action would be MOST affected in vascular smooth muscle?
10. Which receptor type is characterized by intrinsic guanylyl cyclase activity and uses cGMP as its second messenger?
11. Epinephrine activates glycogenolysis in liver via adenylyl cyclase. In this signaling cascade, which step is specifically amplified by the protein kinase A (PKA)-mediated phosphorylation of phosphorylase kinase?
12. A researcher studies cells treated with pertussis toxin. Which cellular response will be lost?
13. Thyroid hormone (T3) acts via nuclear receptors. Which of the following best describes the mechanism by which unliganded thyroid hormone receptors (apo-TR) differ from liganded receptors (holo-TR)?
14. In the JAK-STAT signaling pathway activated by growth hormone (GH), which sequence of events correctly describes signal transduction from receptor activation to gene transcription?
15. A patient with type 2 diabetes has insulin resistance. At the cellular level, which post-receptor defect most commonly accounts for impaired glucose uptake in skeletal muscle?
16. Epidermal growth factor (EGF) binds to its receptor and activates RAS–MAP kinase signalling. Which step converts inactive RAS-GDP to active RAS-GTP?
17. Insulin receptor tyrosine kinase phosphorylates IRS-1, which then activates PI3K. The lipid product of PI3K that recruits PDK1 to the membrane is:
18. A patient with multiple endocrine neoplasia type 1 (MEN1) has a gastrinoma. The hormone gastrin acts via which receptor mechanism?
19. Which of the following hormones acts via a JAK-STAT signal transduction pathway?
20. In pseudohypoparathyroidism type Ia (PHP-Ia), PTH levels are high but the end-organ response is absent. The molecular defect is in:
21. Nitric oxide (NO) acts as a second messenger by activating soluble guanylyl cyclase. The mechanism involves: