In which of the following solvents is the solubility of proteins observed?

In $L-malic$ acid and $L-lysine$,what does the $L$ represent?

$A$: The polypeptide coil of collagen helix is strengthened by the establishment of hydrogen bonds between the $>NH$ group of the glycine residue of each strand and the $-CO$ group of the other two strands.
$R$: In the collagen helix,a locking effect also occurs with the help of proline and hydroxyproline amino acids.

Attempt titrating an amino acid against a weak base and discover the number of dissociating (ionizable) functional groups in the amino acid.

How many iron atoms are present in one quaternary structure of $Hb$ (hemoglobin)?

Hormones thyroxin,adrenaline and the pigment melanin are formed from