BCMB20002 Lecture Notes - Lecture 4: Molecular Mass, Double Bond, Disulfide
23 Jul 2018
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Double bond gives rigidity and planarity (o,c,n,nh,ca) Trans is more stable except for proline. Written n to c (disulphides are covalent bonds) Weights of residues + 2 (for hydrogens) and 16 (oxygen) General: number of residues * 110= molecular weight (daltons) ****means 509 gm of this peptide dissolved in 1000 ml is 1 m or 0. 51 mg dissolved in 1 ml is 1 mm. For ala the nh3 + and coo- interact and there is a wide range of phs where they are ionized. For aaaaaa the separated charges means a narrower ph range where they are ionized. Pk1 (cooh) increases and pk2 (nh3) decreases so as coo becomes more remote it is less available to stabilize with nh3. Observation: pka for amino acid residues varies significantly in proteins compared to those for free amino acids; the presence of near-by charge to a residue will shift its pka significantly.
