Protein kinases – role and functioning MCQs With Answer

Protein kinases are enzymes that catalyze reversible protein phosphorylation, a key post‑translational modification controlling signal transduction, enzyme regulation, cell cycle, and apoptosis. For B. Pharm students, understanding kinase families (Ser/Thr, Tyr, dual‑specificity), structural motifs (ATP‑binding glycine loop, DFG and HRD motifs, activation loop), regulatory mechanisms (autophosphorylation, scaffolds, feedback), and pharmacology (ATP‑competitive, allosteric and covalent inhibitors, selectivity, IC50/Ki) is essential for drug discovery. Practical knowledge of kinase assays, phospho‑antibodies, and clinical kinase inhibitors links biochemistry to therapeutics. Focus on mechanistic details relevant for drug development and pharmacotherapy. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which chemical change is directly catalyzed by protein kinases?

• Transfer of a phosphate group from ATP to a hydroxyl group on a protein
• Hydrolysis of peptide bonds in a protein
• Addition of a methyl group to lysine residues
• Removal of ubiquitin from target proteins

Correct Answer: Transfer of a phosphate group from ATP to a hydroxyl group on a protein

Q2. Serine/threonine kinases primarily phosphorylate which amino acid residues?

• Tryptophan and tyrosine
• Serine and threonine
• Lysine and arginine
• Histidine and aspartate

Correct Answer: Serine and threonine

Q3. The highly conserved “DFG” motif in protein kinases is located in which structural element and is important for what?

• Glycine-rich loop; substrate docking
• Activation loop; coordinating Mg2+ and ATP binding configuration
• C-terminal tail; nuclear localization
• Hinge region; receptor binding

Correct Answer: Activation loop; coordinating Mg2+ and ATP binding configuration

Q4. The HRD motif in the catalytic loop of kinases contains a conserved aspartate. What is the primary role of that aspartate?

• Acts as a general acid to protonate leaving group
• Coordinates metal ion required for stability
• Serves as a catalytic base to orient the substrate hydroxyl for nucleophilic attack
• Binds regulatory subunits

Correct Answer: Serves as a catalytic base to orient the substrate hydroxyl for nucleophilic attack

Q5. Which short sequence motif is characteristic of the ATP‑binding glycine-rich loop in the kinase N‑lobe?

• GxGxxG
• HRD
• DFG
• PxSP

Correct Answer: GxGxxG

Q6. What is the effect of phosphorylation of the activation loop in many kinases?

• Locks the kinase in an inactive conformation by blocking ATP binding
• Promotes a conformational change that increases catalytic activity
• Targets the kinase for proteasomal degradation
• Prevents substrate recruitment to the active site

Correct Answer: Promotes a conformational change that increases catalytic activity

Q7. Autophosphorylation can occur in cis or trans. Which statement best describes trans‑autophosphorylation?

• A kinase phosphorylates an adjacent residue within the same polypeptide chain
• Two kinase molecules phosphorylate each other across a dimer interface
• Phosphorylation occurs only after proteolytic cleavage
• Autophosphorylation that requires a phosphatase first

Correct Answer: Two kinase molecules phosphorylate each other across a dimer interface

Q8. Which of the following is a well-known dual‑specificity kinase that phosphorylates both Thr/Ser and Tyr residues in MAPK signaling?

• MEK (MAP2K)
• PKA
• Src
• CDK2

Correct Answer: MEK (MAP2K)

Q9. The PKA consensus phosphorylation sequence is often described as which motif?

• YXXP
• RRXS/T
• PXSP
• GDYF

Correct Answer: RRXS/T

Q10. ATP‑competitive kinase inhibitors typically bind to which site on the kinase?

• Substrate docking groove remote from active site
• ATP binding pocket within the catalytic cleft
• SH2 domain binding site
• Protein‑protein interaction interface only

Correct Answer: ATP binding pocket within the catalytic cleft

Q11. Which drug is a classical ATP‑competitive inhibitor of the BCR‑ABL tyrosine kinase used in chronic myeloid leukemia?

• Imatinib
• Trametinib
• Rapamycin
• Bevacizumab

Correct Answer: Imatinib

Q12. What is the main advantage of allosteric kinase inhibitors compared with ATP‑competitive inhibitors?

• They are always irreversible
• They can achieve higher selectivity by binding to unique regulatory pockets
• They do not require knowledge of kinase structure
• They increase ATP affinity to boost kinase activity

Correct Answer: They can achieve higher selectivity by binding to unique regulatory pockets

Q13. The “gatekeeper” residue in the ATP pocket influences inhibitor sensitivity. Mutation of the gatekeeper often leads to what clinical problem?

• Enhanced drug clearance by the liver
• Resistance to ATP‑competitive kinase inhibitors
• Increased kinase degradation
• Reduced need for Mg2+ cofactor

Correct Answer: Resistance to ATP‑competitive kinase inhibitors

Q14. Which metal ion is most commonly required as a cofactor for kinase catalytic activity?

• Zn2+
• Mg2+
• Ca2+
• Fe2+

Correct Answer: Mg2+

Q15. Radiometric kinase assays measure which endpoint directly?

• Release of ADP using fluorescence
• Incorporation of radioactive phosphate into substrate
• Change in circular dichroism signal
• Proteolytic cleavage of a labeled peptide

Correct Answer: Incorporation of radioactive phosphate into substrate

Q16. The Cheng–Prusoff equation relates IC50 to Ki. If ATP concentration increases in an assay for a reversible competitive inhibitor, what happens to the measured IC50?

• IC50 decreases
• IC50 increases
• IC50 remains unchanged
• IC50 becomes negative

Correct Answer: IC50 increases

Q17. Phosphatases counteract kinases. Which enzyme family primarily removes serine/threonine phosphorylation?

• PTEN family
• Protein phosphatase 2A (PP2A) and PPP family
• Tyrosine phosphatase family (PTP)
• E3 ubiquitin ligases

Correct Answer: Protein phosphatase 2A (PP2A) and PPP family

Q18. Receptor tyrosine kinases (RTKs) are typically activated by which mechanism after ligand binding?

• Monomeric activation without conformational change
• Dimerization and trans‑autophosphorylation of intracellular kinase domains
• Cleavage of the extracellular domain and nuclear translocation
• Direct GDP/GTP exchange on the receptor

Correct Answer: Dimerization and trans‑autophosphorylation of intracellular kinase domains

Q19. Cyclin‑dependent kinases (CDKs) require cyclins for activity. What additional regulatory event is often needed for full CDK activation?

• Ubiquitination of the cyclin partner
• Phosphorylation of the CDK activation loop by CAK
• Proteolytic cleavage of the CDK N‑terminus
• Binding of GTP in the active site

Correct Answer: Phosphorylation of the CDK activation loop by CAK

Q20. Scaffold proteins in kinase cascades primarily function to:

• Increase the degradation rate of kinases
• Physically organize kinases to enhance signal specificity and efficiency
• Phosphorylate substrates directly
• Transport ATP into the nucleus

Correct Answer: Physically organize kinases to enhance signal specificity and efficiency

Q21. Covalent kinase inhibitors often target which amino acid side chain near the ATP site?

• Phenylalanine aromatic ring
• Cysteine thiol
• Proline imino group
• Methionine thioether

Correct Answer: Cysteine thiol

Q22. Which analytical technique provides site‑specific identification and quantitation of phosphorylation across many proteins (phosphoproteomics)?

• ELISA with total protein antibody
• Mass spectrometry (LC‑MS/MS)
• Standard light microscopy
• Size exclusion chromatography

Correct Answer: Mass spectrometry (LC‑MS/MS)

Q23. SH2 domains recognize which post‑translational modification on target proteins?

• Methylated lysine
• Phosphotyrosine within specific sequence context
• Sumoylated serine
• Glycosylated asparagine

Correct Answer: Phosphotyrosine within specific sequence context

Q24. Which property of the ATP pocket makes achieving inhibitor selectivity challenging?

• High sequence variability among kinases
• Conserved structural features across the kinome
• Absence of any hydrophobic residues
• Strictly membrane‑embedded location

Correct Answer: Conserved structural features across the kinome

Q25. Trametinib is an example of which class of kinase inhibitor?

• ATP‑competitive EGFR inhibitor
• Allosteric MEK inhibitor
• Covalent BTK inhibitor
• mTOR active‑site inhibitor

Correct Answer: Allosteric MEK inhibitor

Q26. The nucleophile that attacks the gamma phosphate of ATP during catalysis is which atom on the substrate?

• Nitrogen of lysine side chain
• Oxygen of the hydroxyl group on Ser/Thr/Tyr
• Sulfur of cysteine
• Carbonyl oxygen of peptide backbone

Correct Answer: Oxygen of the hydroxyl group on Ser/Thr/Tyr

Q27. The T315I mutation in BCR‑ABL confers resistance by what mechanism?

• Enhancing ATP hydrolysis rate to outcompete inhibitors
• Substituting the gatekeeper residue to sterically block inhibitor binding
• Increasing kinase autodegradation
• Reducing expression of the BCR‑ABL protein

Correct Answer: Substituting the gatekeeper residue to sterically block inhibitor binding

Q28. When designing kinase inhibitor assays, why is it important to choose an ATP concentration near physiological or Km for ATP?

• To minimize substrate instability
• ATP concentration does not affect inhibitor potency measurements
• Because inhibitor potency and mechanism (competitive vs noncompetitive) depend on ATP concentration relative to Km
• To prevent protein aggregation

Correct Answer: Because inhibitor potency and mechanism (competitive vs noncompetitive) depend on ATP concentration relative to Km

Q29. Off‑target inhibition of kinases by therapeutic inhibitors can cause adverse effects. Which clinical toxicity is commonly associated with some kinase inhibitors?

• Hypersalivation only
• Cardiotoxicity, including QT prolongation or heart failure
• Complete immune suppression in all patients
• Immediate renal failure independent of dose

Correct Answer: Cardiotoxicity, including QT prolongation or heart failure

Q30. Which experimental tool is most appropriate to detect phosphorylation at a specific residue on a protein in cell lysates?

• Use of a phosphorylation‑site specific antibody in western blot
• Total protein stain without antibody
• Genomic PCR for the kinase gene
• ELISA measuring ATP concentration

Correct Answer: Use of a phosphorylation‑site specific antibody in western blot

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