Lab # 2: Some Properties of Amino Acid and Proteins
Jenna Downey
Friday Lab # 16
Results:
Part 1) table
Biuret test
Ninhydrin test
Xanthoproteic test
diluted egg albumin
purple
clear
yellow
2% gelatin
purple
very slight pink/red
Light yellow
skim milk
purple
purple
yellow with clumps at
surface
0.1M glutamic acid
blue
clear
clear
0.1M valine
blue
clear
clear
0.025M tyrosine
blue
very light red/purple
yellow
0.1M sucrose
blue
clear
clear
Part 2) TLC Plate
Calculations:
1- Aspartic acid = 8/60 = 0.13mm
2- Glutamic acid = 10/60 =0.17mm
3 - Glycine = 16/60 = 0.27mm
4 - Valine = 52/60 = 0.87mm
5 - Phenylalanine = 36/60 = 0.6mm
6 - Unknown (#1) = 35/60 = 0.59mm
Chemical Reactions:
1. An amino acid with ninhydrin  imine product
2. Mono-nitration of tyrosine
Questions:
1. All three proteins within the xanthoproteic test produced positive results, which included diluted
egg albumin, skim milk and 2% gelatin produced yellow coloring in the protein. Gelatin is a
mixture of peptides and proteins. The results of gelatin were a lighter yellow color, as it contains
amino acids (proline, glycine, and hydroproline) which do not have aromatic rings, with only
small trace amount of tyrosine, an amino acid containing an aromatic ring explaining for the faint
yellow coloring. This conclusion came from tyrosine, being the only amino acid within this test
producing a positive yellow result.
tyrosine.
2. Amino acids tested in this lab are ranked from smallest to highest based upon their Rf values;
Aspartic acid, Glutamic acid, Glycine, Unknown 1, Phenylalanine, and Valine. Aspartic acid and
glutamic acid are polar molecules due to –OH, NH2, and C=O functional groups. Therefore they
have a stronger adsorption into the silica gel. Glycine, contain same functional groups, but the
amounts are decreased, therefore allowing glycine to be less polar (i.e. traveling up the TLC plate
a further distance). Unknown 1 and phenylalanine show near identical polarities, due to their Rf
value, concluding that they are the same amino acid. Valine, through my test showed to be lest
polar. Upon research its structure shows an isopropyl side chain. When compared to
phenylalanine’s benzene ring, I believe its suffice to conclude that valine should have a lower Rf
value then phenylalanine although my TLC plate does not show such conclusion.