(a) Give structure of t-RNA. Write role of different RNAs in the translation process. (20 marks) (b) Describe the principle and…

Part (a): t-RNA and translation RNAs t-RNA is a small RNA (~70–90 nt) whose secondary structure is a cloverleaf formed by intramolecular base pairing. It has an acceptor stem ending in an unpaired 3′-CCA terminus, to which the amino acid is esterified at the 3′-OH of the terminal adenosine. The DHU loop contains dihydrouridine residues; the TΨC loop contains thymidine and pseudouridine; the anticodon loop carries the three-base anticodon and is flanked by a conserved uridine on the 5′ side and a hypermodified purine on the 3′ side. A variable loop completes the cloverleaf. In solution it folds into an L-shaped tertiary structure, in which the D and TΨC stems stack, and modified bases and hydrogen bonds position the amino-acid end and anticodon at opposite ends.

In translation, mRNA is the template: its 5′ cap and 3′ poly-A tail (eukaryotes) or Shine-Dalgarno sequence (prokaryotes) help ribosome positioning, while codons specify amino acids. t-RNA is the adaptor: aminoacyl-tRNA synthetases charge it with the cognate amino acid, and its anticodon pairs with the mRNA codon in the ribosome A site. r-RNA is structural and catalytic: 16S/18S rRNA in the small subunit helps mRNA binding and decoding, while 23S/28S and 5S rRNA in the large subunit form the peptidyl-transferase centre. In prokaryotes 16S rRNA pairs with the Shine-Dalgarno sequence; in eukaryotes initiation is cap-dependent scanning, not base-pairing by 18S rRNA. Small regulatory RNAs can also influence initiation or termination by binding mRNA and affecting ribosome access or stability.

Part (b): Whole animal cloning Whole animal cloning is reproductive somatic-cell nuclear transfer (SCNT). Its principle is genomic equivalence: a differentiated somatic nucleus contains the full genome, and oocyte cytoplasmic factors epigenetically reprogram it to totipotency, allowing development into an embryo. This differs from therapeutic cloning, where SCNT yields embryonic stem cells for research or therapy rather than an animal.

The method begins with a donor somatic cell, usually a fibroblast. A mature oocyte is enucleated by removing the first polar body or germinal vesicle. The donor cell is introduced into the enucleated oocyte and fused by electric pulse or chemical means. The reconstructed oocyte is activated, often by calcium ionophore or electric stimulation, to initiate division. It is cultured in vitro to the blastocyst stage, then transferred to a surrogate. The offspring is genetically identical to the nuclear donor, though mitochondrial DNA derives mainly from the oocyte. Dolly the sheep (1997) demonstrated the principle; in India, Garima II, a cloned buffalo reported from NDRI, Karnal, showed its livestock application.

Part (c): Miller experiment Stanley Miller, with Harold Urey, simulated early-Earth conditions in a closed apparatus. A flask of water was heated to produce steam, and a reducing gas mixture of methane, ammonia and hydrogen—commonly taken as CH4:NH3:H2 = 2:1:2, with water vapour separate—was circulated. Electric sparks provided energy, a condenser cooled the vapours, and a trap collected the condensed liquids. The experiment yielded small organic monomers, especially glycine and alanine, along with hydroxy acids and other simple organic compounds. It did not produce macromolecules or cells, but it showed that prebiotic energy could convert simple inorganic gases into biologically relevant building blocks.

Thus the experiment supported the Oparin-Haldane primordial-soup idea of chemical evolution: non-living organic molecules accumulated in the early environment, later forming more complex systems before biological evolution began. It provided experimental support, not proof, for that theory.

Together, these topics trace biological organisation from molecules to organisms: translation machinery decodes genetic information, reproductive biotechnology manipulates whole organisms, and prebiotic chemistry explains how the molecular precursors of life may have arisen.