What is the expanded form of the term ‘mRNA’ that has been widely discussed since the beginning of the pandemic?

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Correct — A, Messenger Ribonucleic Acid. The name describes the job. A gene is a stretch of DNA stored in the nucleus, and the ribosomes that actually build proteins sit outside it in the cytoplasm, so the instruction has to be carried across. Transcription copies one gene into a single strand of RNA; that strand leaves the nucleus, docks with a ribosome, and is read three bases at a time, each triplet or codon calling up one amino acid until a complete protein chain has been assembled. The RNA does nothing but carry the message, and is then degraded — which is why it was named the messenger. The naming is documented: Sydney Brenner and Francis Crick conceived the idea on 15 April 1960 at King's College, Cambridge, while François Jacob described the Paris experiments to them; the molecule was experimentally characterised in May 1961 in two back-to-back papers in Nature, one by Brenner, Jacob and Meselson and one by Gros and colleagues; and it was Jacob with Jacques Monod who coined the term 'messenger RNA'. The pandemic framing in the stem points at the vaccine platform that made the acronym a household word: Pfizer-BioNTech's Comirnaty and Moderna's Spikevax, first authorised in December 2020, and India's own self-amplifying GEMCOVAC-19 from Gennova Biopharmaceuticals, all work by supplying that middle step ready-made — a synthetic messenger for the SARS-CoV-2 spike protein, wrapped in a lipid nanoparticle so it survives long enough to reach a cell, which then manufactures the antigen itself. Days after this paper was sat, on 2 October 2023, Katalin Karikó and Drew Weissman were announced as winners of the Nobel Prize in Physiology or Medicine for the chemistry that made those vaccines possible.

Why the other options are wrong — (b) No molecule of this name exists. The option trades on a genuine confusion from the pandemic years: SARS-CoV-2's own genome is RNA, and changes in that genome are what produced the named variants — Alpha, Delta, Omicron. But that is the virus's hereditary material mutating, an entirely different thing from the cell's messenger RNA, and a mutation is an event that happens to a sequence, never a class of molecule.  (c) The one distractor with a real fact behind it, and the reason a well-read candidate can talk himself out of the right answer. The mRNA inside Comirnaty and Spikevax genuinely is chemically modified — every uridine is replaced by N1-methylpseudouridine so the innate immune system does not destroy the strand on arrival — and that single modification is precisely what the 2023 Nobel Prize in Physiology or Medicine honoured. But 'm' has stood for messenger since Jacob and Monod named the molecule in 1961, six decades before nucleoside modification existed. The chemistry is real; the expansion is not.  (d) A pure decoy, built to be plausible to a candidate reasoning from the English word rather than the biology. 'Mnemonic' means aiding memory, and since mRNA does carry information the word can feel almost right. There is no molecule so named, and the analogy fails anyway: mRNA is a short-lived working copy that the cell destroys after use, so if anything it is the opposite of a memory device — the archive is the DNA.

Concept: The central dogma of molecular biology, set out by Francis Crick in 1958, describes the one-way flow of sequence information in a cell: DNA is replicated, transcribed into RNA, and the RNA is translated into protein. Three kinds of RNA divide the work of that last stage. Messenger RNA carries the copied instruction from gene to ribosome. Transfer RNA fetches the correct amino acid for each codon and holds the anticodon that pairs with it. Ribosomal RNA, together with proteins, builds the ribosome itself and catalyses the peptide bond. RNA differs from DNA on three structural counts — it uses the sugar ribose rather than deoxyribose, the base uracil rather than thymine, and it is usually single-stranded rather than a double helix. Eukaryotic mRNA is further processed before it leaves the nucleus: introns are spliced out, a 7-methylguanosine cap is added at the 5' end and a poly(A) tail at the 3' end, both of which protect the strand from being chewed up by enzymes. Its short life is the point — a messenger that persisted would keep making protein the cell no longer needs, so mRNA is deliberately disposable.

State PCS 2023 Q25 — Science & Technology PYQ with Answer

State PCS 2023 Q25 — Science & Technology PYQ with Answer