Question

Speculate on why valine and isoleucine conformations are more restricted than some other residues and conversely, why glycine is not so restricted.

Answer 1

ISOLUCINE is an ɑ-amino acid that is used in the biosynthesisof proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and a hydrocarbon side chain, classifying it as a non-polar, uncharged(at physiological pH), aliphatic amino acid. It is essential in humans, meaning the body cannot synthesize it, and must be ingested in our diet. Isoleucine is synthesized from pyruvate employing leucine biosynthesis enzymes in other organisms such as bacteria. Inability to break down isoleucine, along with other amino acids, is associated with the disease called Maple Syrup Urine Disease, which results in discoloration and a sweet smell in the patient's urine, which is where the name comes from. However in severe cases, MSUD can lead to damage to the brain cells and ultimately death.

is the smallest of the 20 amino acids commonly found in proteins, and indeed is the smallest possible (having a hydrogen substituent as its side-chain). The formula is NH₂CH₂COOH. Its codons are GGU, GGC, GGA, GGG of the genetic code.

VALINE encoded by the codons GUU, GUC, GUA, and GUG is an ɑ-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and a side chain isopropyl variable group, classifying it as a non-polar amino acid. It is essential in humans, meaning the body cannot synthesize it and thus it must be obtained from the diet. Human dietary sources are any proteinaceous foods such as meats, dairy products, soy products, beans and legumes.

Along with leucine and isoleucine, valine is a branched-chain amino acid. In sickle-cell disease, valine substitutes for the hydrophilic amino acid glutamic acid in β-globin. Because valine is hydrophobic, the hemoglobin is prone to abnormal aggregation.

GLYCINE is a colourless, sweet-tasting crystalline solid. It is unique among the proteinogenic amino acids in that it is achiral. It can fit into hydrophilic or hydrophobic environments^{[citation needed]}, due to its minimal side chain of only one hydrogen atom.

The main reasons for the glysine is not restricted because small, and lower molecular mass.