Relative contents of acidic and basic residues (gel with pH gradient is used) ▪ Isoelectric focusing = gel electrophoresis method that separates proteins on basis of their ▪ pI is determined by averaging the pKa values that refer to the protonation and Done by either acid/base hydrolysis (nonspecific) or with the help of proteolytic ▪ The process of breaking the peptide bond However, this is still free rotation around the ALPHA CARBON ▪ The bond when formed has a lot of resonance delocalization (partial double bond ▪ The nucleophilic amino group attacking an electrophilic carbonyl ▪ Peptide bonds are formed by the nucleophilic addition-elimination ( condensation, dehydration rxn) reaction between the carboxyl group of one amino acid and the amino group of another amino acid ▪ Peptide bonds link amino acid chains together O Peptide linkage: polypeptides and proteins ▪ Cystine = 2 cysteines that have formed a disulfide bond ▪ Cysteine = amino acid with the thiol R group O Sulfur linkage for cysteine and cystine ![]() M), Phenylalanine (Phe, F), Valine (Val, V), Proline (Pro, P), Glycine O Alanine (Ala, A), Isoleucine (Ile, I), Leucine (Leu, L), Methionine (Met, HYDROPHOBIC: If the R group DOES NOT contain what is listed above ^^ H), Serine (Ser, S), Threonine (Thr, T), Tyrosine (Tyr, Y), Cysteine (Cys, O Arginine (Arg, R), Lysine (Lys, K), Aspartic Acid (Asp, D), GlutamicĪcid (Glu, E), Glutamine (Gln, Q), Asparagine (Asn, N), Histidine (His, HYDROPHILIC: If the R group contains acids, bases, amines or alcohols BASIC: Lysine (Lys, K) Arginine (Arg, K) Histidine (His, H) ACIDIC: Aspartic Acid (Asp, D) Glutamic Acid (Glu, E) ▪ At pH = pI, amino acid = zwitterionic (neutral) ▪ EVERY AA has S configuration EXCEPT FOR cysteine (R configuration) ▪ The alpha carbon IN EVERY amino acid is a chiral center EXCEPT in glycine (it is O Absolute configuration at the α position
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