Q. 40 Which one of the following is an incorrect biomolecule-modification pair?
(A)Lipid – Palmitoylation
(B) DNA and Protein – Methylation
(C) Protein – Glycosylation
(D) RNA – Polyadenylation
The incorrect biomolecule-modification pair is RNA – Polyadenylation, making option (D) the right choice in this biology MCQ. This question tests knowledge of post-translational and post-transcriptional modifications in biomolecules like lipids, DNA, proteins, and RNA. Understanding these pairs is crucial for exams like CSIR NET, GATE Biotechnology, and molecular biology coursework.
Correct Answer
Option (D) RNA – Polyadenylation is incorrect. Polyadenylation refers to adding a poly(A) tail primarily to messenger RNA (mRNA) during processing, but it is not a standard modification for all RNA types like tRNA or rRNA, which lack stable poly(A) tails in eukaryotes. While some non-coding RNAs or rRNAs can undergo transient polyadenylation for degradation, it is not a defining or stable modification for RNA as a biomolecule class, unlike the other options.
Option Breakdown
(A) Lipid – Palmitoylation: Correct Pair
Palmitoylation attaches palmitic acid (a 16-carbon fatty acid lipid) to proteins or sometimes lipids, enhancing membrane association and signaling. This reversible modification occurs on cysteine residues via thioester bonds.
(B) DNA and Protein – Methylation: Correct Pair
DNA methylation adds methyl groups to cytosine bases (e.g., 5-methylcytosine) for gene regulation and epigenetics. Protein methylation targets lysine or arginine residues, affecting histone function and signaling pathways.
(C) Protein – Glycosylation: Correct Pair
Glycosylation covalently links carbohydrates to proteins (N-linked to asparagine or O-linked to serine/threonine), aiding protein folding, stability, and cell recognition in the ER and Golgi.
(D) RNA – Polyadenylation: Incorrect Pair
Polyadenylation adds ~200 adenine nucleotides to the 3′ end of pre-mRNA for stability, export, and translation, but mature tRNA, rRNA, and most non-coding RNAs do not receive stable poly(A) tails—making this pairing imprecise for RNA broadly.
