Q.25 The protein in eukaryotes which is subjected to degradation undergoes
- (A) phosphorylation
- (B) carboxylation
- (C) ubiquitination
- (D) methylation
The protein in eukaryotes which is subjected to degradation undergoes ubiquitination, marking it for destruction by the 26S proteasome. This SEO-optimized article answers the MCQ: The protein in eukaryotes which is subjected to degradation undergoes (A) phosphorylation, (B) carboxylation, (C) ubiquitination, (D) methylation—essential for cell biology, biochemistry, and biotechnology students studying protein quality control.
Correct Answer: Option (C) Ubiquitination
Ubiquitination involves covalent attachment of ubiquitin (76-amino acid protein) to lysine residues on target proteins via E1 (activating), E2 (conjugating), and E3 (ligating) enzymes. Polyubiquitin chains (K48-linked) signal 26S proteasome recognition, unfolding, and degradation into peptides and recycled ubiquitin.
This ATP-dependent pathway handles ~80% of cytosolic/nuclear protein turnover, regulating cell cycle (cyclins), signaling (IKB), and misfolded proteins from chaperone failures (Q.19).
Explanation of All Options
Each represents post-translational modification but with different cellular roles:
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(A) Phosphorylation: Incorrect. Regulates activity/localization (kinases/phosphatases); doesn’t target degradation.
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(B) Carboxylation: Incorrect. Vitamin K-dependent modification (glutamic acid → gamma-carboxyglutamate) for calcium binding in coagulation factors.
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(C) Ubiquitination: Correct. Primary eukaryotic degradation signal via ubiquitin-proteasome system.
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(D) Methylation: Incorrect. Epigenetic (histones) or stability (p53) modifications; not degradation signal.
Option Modification Type Enzyme Classes Primary Function Degradation Signal? (A) Phosphorylation Phosphate addition Kinases Activity regulation No (B) Carboxylation CO2 addition Carboxylases Ca²⁺ binding No (C) Ubiquitination Ubiquitin conjugation E1/E2/E3 Protein degradation Yes (D) Methylation Methyl addition Methyltransferases Epigenetics/stability No Biotechnology Relevance
Ubiquitin pathway engineering enhances recombinant protein production (Q.5) by degrading inclusion bodies, supports hairy root stability (Q.11), and enables selectable marker degradation timing (Q.23 antibiotics). Proteasome inhibitors (bortezomib) treat multiple myeloma.
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