“Are the atoms of the dextroacid (tartaric) grouped in the spirals of a right-hand helix or situated at the angles of an irregular tetrahedron, or arranged in such or such particular unsymmetrical fashion? We are unable to reply to these questions. But there can be no reason for doubting that the grouping of the atoms has an unsymmetrical arrangement with a non-superimposable image. It is not less certain that the atoms of the laevo-acid realize precisely an unsymmetrical arrangement of the inverse of the above.”
![“[The] structural theory is of extreme simplicity. It assumes that the molecule is held together by links between one atom and the next: that every kind of atom can form a definite small number of such links: that these can be single, double or triple: that the groups may take up any position…” quote by Nevil Vincent Sidgwick](https://sms4smile.com/quotes/img-quotes/0d0/nevil-vincent-sidgwick-133243_chemistry_the-structural-theory-is-of-extreme-simp_403895.jpg)
![“In describing a protein it is now common to distinguish the primary, secondary and tertiary structures. The primary structure is simply the order, or sequence, of the amino-acid residues along the polypeptide chains. This was first determined by [Frederick] Sanger using chemical techniques for the…” quote by John Kendrew](https://sms4smile.com/quotes/img-quotes/805/john-kendrew-166387_amino-acid_in-describing-a-protein-it-is-now-common_1314282.jpg)
