• Chemical Structure of Aspartame: Aspartame is an artificial, non-nutritive dipeptide sweetener chemically designated as L-aspartyl-L-phenylalanine methyl ester ($N$-L-$\alpha$-aspartyl-L-phenylalanine 1-methyl ester).
• Stereospecificity of Taste: Only the L,L-enantiomer binds productively to human sweet-taste receptor heterodimers (T1R2/T1R3), providing approximately 180–200 times the sweetness of sucrose.
• Inactivity of Other Isomers: The stereoisomeric forms (such as D-aspartyl-L-phenylalanine methyl ester or D-aspartyl-D-phenylalanine methyl ester) taste intensely bitter or completely tasteless.

Correct option: (4) L-aspartyl-L-phenylalanine methyl ester

• 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