Basic Biochemistry & Biomolecules

• Discovery of Asparagine (1806): Asparagine was the very first amino acid isolated and identified, discovered in 1806 by French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet from the juice of asparagus seedlings (Asparagus officinalis).
• Chronology of Other Amino Acids: Glycine was isolated from gelatin in 1820; leucine in 1820; alanine was synthesized in 1850; threonine was the last of the standard 20 amino acids to be discovered (by William Cumming Rose in 1935).

Correct option: (4) Asparagine

• Assertion (A) is True: Archaebacteria (Archaea) thrive in extreme terrestrial and marine environments, including hyperthermal vents ($\gt 100^\circ\text{C}$), hypersaline lakes, and highly acidic solfataras (pH $\lt 2$).
• Reason (R) is False: Archaebacterial cell membranes possess unique isoprenoid phytanyl chains linked to glycerol via ether bonds ($-\text{C}-\text{O}-\text{C}-$), NOT ester bonds. Ether linkages and cyclopentane rings provide far greater chemical resilience against thermal degradation and acid hydrolysis than the ester bonds ($-\text{COO}-$) found in eubacteria and eukaryotes.
• Conclusion: (A) is true but (R) is false.

Correct option: (3) (A) is true but (R) is false.

• Essential Amino Acid Classification: Essential amino acids cannot be synthesized de novo by humans and monogastric animals and must be supplied through dietary intake: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine.
• Agronomic Context: Lysine is typically the first limiting essential amino acid in cereal grains (wheat, rice, maize), whereas methionine is the first limiting amino acid in pulses/legumes (soybean, chickpea).
• Non-essential Amino Acids: Glycine, proline, alanine, and glutamic acid are non-essential as they are readily synthesized from glycolytic and TCA cycle intermediates.

Correct option: (2) Lysine and methionine

• Assertion (A) is True: In supramolecular complexes (such as multi-enzyme complexes, ribosome subunits, and biological membranes), hundreds of cooperative weak interactions (hydrogen bonds, ionic interactions, hydrophobic effects, and van der Waals forces) stabilize the quaternary architecture.
• Reason (R) is False: Supramolecular complexes are held together by non-covalent interactions, not covalent bonds. This allows rapid assembly, conformational flexibility, and dynamic disassembly in response to physiological regulatory signals.
• Conclusion: (A) is true but (R) is false.

Correct option: (3) (A) is true but (R) is false.