Phenylalanine

MW: 165.19

Phenylalanine (2-Amino-3-phenylpropanoic acid) has a symbol of F.⁷ Phenylalanine is a water-soluble amino acid that builds blocks for proteins in the body, which means the body needs it for health because it cannot make it. Phenylalanine is found in three forms: L-phenylalanine, which is the natural form found in proteins; D-phenylalanine, which is a mirror image of L-phenylalanine that is made in a laboratory, and DL-phenylalanine, a combination of both the forms.¹ Phenylalanine is an essential amino acid that is nonpolar because of the hydrophobic nature of the benzyl side chain.²

Amino group: (-NH₂)

Carboxylic acid group (-COOH)

Hydrogen Group (H)

The side chain in phenylalanine composed of just carbons and hydrogens atoms.








PKA Values

The equation for pKa is: pKa = -log Ka

To find the Ka, you do this:
Ka = [H+] x [X-]/[HX]

Ka is always products over reactants.³

The Pka values of phenylalanine are 2.58 and 9.24.

Isoelectric Point

For simple amino acids, in which the R group doesn't contain any titratable groups, the isoelectric point can be calculated by averaging the pK_a values for the a-carboxylic acid and a-amino groups.⁴

α -COOH pK_a is 1.8 and  α-NH₃ pK_a is 9.1

1.8 + 9.1/ 2 = 5.45

Phenylalanine isoelectric point:  5.45

IR Spectrum⁸

 

Polypeptides

  
Amino acids consists of a central carbon atom chemically bonded to one hydrogen atom (H), one carboxylic acid group (-COOH), one amino (nitrogen-containing) group (-NH₂), and one side group unique to each amino acid (R).⁹ The side group differs in shape, size, pH, and composition and gives each amino acid its identity. Peptides are amino acids linked in specific sequences to form strands of protein. One amino acid is joined to another by a peptide bond. A peptide is formed by the carboxyl group (-COOH) and bonds to an amino group (-NH₂) of another amino acid and releases water in the process. A polypeptide contains more then 10 amino acids. When two amino acids join together, the carboxyl group of one amino acid is matched with another amino acid. A condensed reaction forms a peptide bond and releases water.⁹               

This picture shows how phenylalanine and glycine are forming a peptide bond.

Citations:

1.      University of Maryland Medical Center. Phenylalanine.

http://www.umm.edu/altmed/articles/phenylalanine-000318.htm (accessed 2011)

           

2.      Phenylalanine. Encyclopedia.

http://www.absoluteastronomy.com/topics/Phenylalanine (accessed 2011)

3.      Amino Acid Structure. Phenylalanine. http://www.cem.msu.edu/~cem252/sp97/ch24/ch24aa.html (accessed 2007)

4.      Amino Acid. The Acid Base Chemistry of Amino Acids. http://chemed.chem.purdue.edu/genchem/topicreview/bp/1biochem/amino2.html (accessed 2006)

5.      Amino Acid Classification for R groups. Phenylalanine. http://mcb.berkeley.edu/courses/mcb102/discussion/Handouts/Amino%20acid%20Review%20JK.pdf

6.      Identifying Amino Acids in Protein NMR Spectra. Phenylalanine. http://hoffman.cm.utexas.edu/research/aa_h_nmr.pdf

7.      X-1A x-ray Absorption Spectra. Phenylalanine. http://xray1.physics.sunysb.edu/~micros/xas/xas.html (accessed Oct. 2, 2003)

 

8.      PhotochemCAD Spectra by Category. Phenylalanine. http://omlc.ogi.edu/spectra/PhotochemCAD/html/phenylalanine.html (accessed 1998)

9.      Nutrition. Polypeptide. http://books.google.com/books?id=46o0PzPI07YC&pg=PA208&lpg=PA208&dq=phenylalanine+polypeptide&source=bl&ots=GjuuhrOHPI&sig=nddjO-qClfNNQjCVLS3JnDNX-Yg&hl=en&ei=YISLTafVBdDUgAf14o3JDQ&sa=X&oi=book_result&ct=result&resnum=9&ved=0CF4Q6AEwCA#v=onepage&q=phenylalanine%20polypeptide&f=false (accessed 2004)