Download Lecture 4: Properties of Amino Acids and Peptide Bonds in Medical Biochemistry and more Slides Biochemistry in PDF only on Docsity! Biomolecules: Amino Acids and Peptides Lecture 4, Medical Biochemistry Docsity.com Lecture 4 Outline • Present and discuss the properties of amino acids • Discuss the importance of pKa values and amino acid titration curves • NOTE: Ignore the techniques section in your book chapter 4 (p. 33-34) Docsity.com COO™
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Aspartate Glutamate.
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B. Basic amino acids
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Histidine
Lysine ':
Non-protein Amino Acids
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pAminobutyricacid (GABA) Histamine» =~ Dopamine Thyroxine *
CH, —-C=N CH,—CH,~$H
Hj—CH—COO- —-H,N—CH—CO0-
p-Cya*oalanine Homocysteine
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HN 7 CH—COO-
Azaserine S-Adenosylmethionine
pKap (NH3)=9.8
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1.0
Equivalents of OH~
COOH coo” coo”
H3N-CH, <—® H,N-—CH, +—> H,N-CH,
Below Between Above
pH 2.4 pH 2.4 and 9.8 pH 9.8
Predominant species
pK (CtNHg)=9.3
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pH 1.8 and 6.0 pH 6.0 and 9.3
Predominant species
Aspartate
Glutamate
Histidine
Cysteine
Tyrosine
Lysine
Arginine
Form that predominates
below the pK,
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H CHy = CHy~COOH
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H~ CH;SH
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Planar nature of the peptide bond. The partial double bond characteristic prevents free rotation around the C-N bond; keeping it in the same plane with the attached O and H atoms. These planar bonds can pivot around the shared Ca atom Docsity.com Trans conformation; most common and sterically favored Cis conformation; found rarely with Pro, sterically unfavorable Docsity.com The planar nature of the peptide bond restricts the possible conformations that a protein can assume. This can be predicted by the angle (above or below the peptide bond plane) of the two bonds between the a-carbon of the constituent amino acids. These phi (f) and psi (y) angles can be used to predict and define some higher order protein structures. Peptide Bond Steric Restrictions Docsity.com
