4 public questions tagged with this topic.
Phosphorylation is a major post-translational modification that regulates protein activity.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
Co-translational modifications occur simultaneously with nascent chain elongation inside ribosome exit tunnel, including methionine aminopeptidase removal, N-terminal acetylation, and selenocysteine insertion. Selenocysteine insertion qualifies as cotranslational because SECIS-mediated recoding delivers Sec-tRNASec to A-site before termination, integrating Sec directly into primary sequence during elongation. In contrast, phosphorylation, acetylation, methylation typically occur post-translationally after folding via separate kinases, acetyltransferases, methyltransferases adding functional groups to side chains. This distinction matters for topology and enzyme targeting. Selenocysteine integration requires active ribosome, GTP hydrolysis, mRNA structure, illustrating direct encoding rather than side-chain decoration after polypeptide release from large subunit.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 5: Co-translational vs Post-translational Modifications
Glycosylation adds monosaccharide residues with defined masses to proteins, altering function and stability. N-acetyl glucosamine, GlcNAc, exists as common modification in N-linked and O-linked glycans and O-GlcNAc signaling. Residue mass of HexNAc after dehydration during glycosidic bond formation is 203.079 Da, observed as +203 Da increment on peptide mass spectra. Detecting this shift indicates single GlcNAc attachment, distinct from 162 Da for hexose, 146 Da for fucose, or 291 Da for sialic acid. Recognition of +203 Da aids mapping of glycosylation sites in proteomics studies.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.
Endoplasmic reticulum, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)
