Biomolecules: Amino Acids and Peptides

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Biomolecules Amino Acids and Peptides

• Lecture 4, Medical Biochemistry

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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)

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At physiological pHs (7.0-7.4), both the
carboxyl and amino groups are charged
Only L-amino acids are found in proteins
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Non-protein Amino Acids
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Examples of Clinical Aminoacidurias

• Metabolic defects Phenylketonuria (Phe),
  Tyrosinemias (Phe,Tyr), Maple Syrup Urine Disease
  (Leu, Val, Ile), Alcaptonuria (Tyr)
• Absorption/transport defects cystinuria (Cys),
  Hartnup disease , Fanconis Syndrome
• These diseases are generally diagnosed from
  indicators in the urine or plasma. These diseases
  will be discussed further in the amino acid
  metabolism lectures

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Post-translational Modifications
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BOND
PEPTIDE
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Resonance forms of peptide bonds. The peptide
bond (C) is a hybrid of A and B, giving it a
partial double bond character
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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
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Trans conformation most common and sterically
favored
Cis conformation found rarely with Pro,
sterically unfavorable
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Peptide Bond Steric Restrictions
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.
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Levels of Protein Structure