BCH210H1 Lecture Notes - Lecture 2: Isoleucine, Leucine, Phenylalanine

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6 Apr 2019

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BCH210H1 Full Course Notes

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Document Summary

Notable features: aromatic side chain pka of side chain. Leucine (leu, l: aliphatic side chain, beta-branched, aliphatic side chain. Methionine (met: contains a sulfur, cannot form disulfide bonds. 8 sulfhydryl group: can form disulfide bonds with other cys to create cystine, aliphatic side chain, aliphatic side chain, beta-branched. Lysine (lys, k: basic, charged at physiological ph. 12. 5 group: basic, charged at physiological ph. 4: acidic, physiological form (ph of human body) Glutamine (gln, q: polar, carboxamide group, acidic, physiological form (ph of human body, polar, carboxamide group. Proline (pro, p: aliphatic hydroxyl side chain, can form h- bonds, aliphatic hydroxyl side chain, beta-branched, can form h- bonds, aromatic side. Locks the backbone into a structure not much rotation. Tryptophan (trp, w: aromatic side chain, aliphatic side chain, achiral, very flexible. If an acid is in a more basic environment (higher ph, relative), it will donate its proton and thus become negative.

Related Questions

The peptide hormone vasopressin is used in the regulation of Na+ in many vertebrate. Porcine(pig) vasopressin has the sequence Asp-Tyr-Phe-Glu-Asn-Cys-Pro-Lys-Gly.

a) What is the pI of this peptide? Use the pKa values in the table on the last page for your calculations.

b) Could this peptide have an a helical secondary structure? Why or why not.

c) Will this peptide absorb UV light(280nm)? Why?

Consider the peptide:
NH₂-GAPAGPAGTGKTETTKDLAKSMALLCWFNCS-COOH

Table I. pK values of some amino acids

amino acid	pK of side chain or terminal group
Alanine (Ala or A)	uncharged
Arginine (Arg or R)	12.5
Asparagine (Asn or N)	uncharged
Aspartic acid (Asp or D)	3.9
Cysteine (Cys or C)	8.3
Glutamic acid (Glu or E)	4.3
Glycine (Gly or G)	uncharged
Histidine (His or H)	6.0
Leucine (Leu or L)	uncharged
Lysine (Lys or K)	10.8
Phenylalanine (Phe or F)	uncharged
Serine (Ser or S)	uncharged
Tryptophan (Trp or W)	uncharged
Tyrosine (Tyr or Y)	10.9
Valine (Val or V)	uncharged
peptide N terminus	7.8
peptide C terminus	3.6