Biomolecules and Enzymes

Benfotiamine is a synthetic S-acyl derivative of thiamine (vitamin B1). After absorption, benfotiamine can be dephosphorylated by cells bearing an ecto-alkaline phosphatase to the lipid-soluble S-benzoylthiamine.

An all-β proteins is a class of structural domains in which the secondary structure is composed entirely of β-sheets, with the possible exception of a few isolated α-helices on the periphery. Common examples include the SH3 domain, the beta-propeller domain, the immunoglobulin fold and B3 DNA binding domain.

Hemoglobin is a complex protein (specifically a globular protein) found in red blood cells that contains iron and is responsible for carrying oxygen from the lungs to tissues throughout the body. Each hemoglobin molecule can carry four oxygen molecules. It is not a mineral (though it contains iron), not plasma (the liquid portion of blood), and not simply an 'organic substance' - it is specifically a structured protein with a precise molecular composition essential for respiration.

It functions as an antioxidant and protects our body against radiation and pollutions.

These are proteins linked with various metals. Example: Casein, collagen, ceruloplasmin etc.

The folding of the polypeptide chain is stabilized by weak noncovalent interactions.

Proanthocyanidin is a class of flavanols. Proanthocyanidins are essentially polymer chains of flavonoids such as catechins.

 Gamma globulins are antibodies produced in blood, and not in liver.

Albumin is the most abundant plasma protein.

The sulphur content of proteins is approximately 0-4%. Only two amino acids contain sulphur: cysteine (~2.3% S) and methionine (~3.2% S). Since these constitute a small fraction of total amino acids, the overall sulphur percentage in proteins is very low, making option B correct.

Methionine, Alanine, and Tryptophan are all nonpolar (hydrophobic) amino acids based on their side chains. Methionine has a sulfur-containing alkyl chain, Alanine has a simple methyl group, and Tryptophan has a bulky indole ring - all are hydrophobic. Therefore, 'All of the above' is the correct answer.

Cystine contains a disulfide (-S-S-) bond formed by the oxidation of two cysteine thiol groups. This covalent linkage between two cysteine residues is crucial for protein structure stabilization. Arginine contains guanidino group, threonine has hydroxyl group, and asparagine contains amide group - none have disulfide bonds.

Proteins contain approximately 16% nitrogen by weight, which is used in Kjeldahl method for protein estimation. This constant nitrogen content is due to the peptide bonds linking amino acids. The nitrogen comes from the amino groups present in all amino acids that make up proteins.

Both D-serine and D-aspartate are naturally occurring D-amino acids found in mammalian brain tissue, functioning as neuromodulators and neurotransmitters. D-serine acts as a co-agonist at NMDA receptors, while D-aspartate regulates hormone release. D-alanine is not typically found in brain tissue.

Hopkins-Cole reaction (also called glyoxylic acid test) is specific for tryptophan, which contains an indole ring that reacts with glyoxylic acid in presence of concentrated sulfuric acid to form a purple-colored product. Glycine, serine, and histidine do not contain indole rings and do not give this reaction.