Biology Reference
In-Depth Information
TABLE 6.1 List of Non-Polar and Polar Amino Acids.
Non-polar
Polar
Alanine (ala, A)
Glycine (gly, G)
Valine (val, V)
Serine (ser, S)
Leucine (leu, L)
Threonine (the, T)
Isoleucine (ile, I)
Cystine (cys, C)
Proline (pro, P)
Glutamine (gln, Q)
Phenylalanine (phe, F)
Tyrosine (tyr, Y)
Tryptophan (trp, W)
Asparagine (asn, N)
Methionine (met, M)
Lysine (lys, K)
Arginine (arg, R)
Histidine (his, H)
Glutamic Acid (glu, E)
Aspartic Acid (asp, D)
Tabl e 6 .1 presents a simple classification system that was first used to compare water-
soluble and membrane proteins. By this analysis an initial comparison was made between
two mitochondrial proteins, the very water-soluble cytochrome C and the very water-insoluble
mitochondrial 'structural protein.' Surprisingly, both proteins had almost identical ratios of
polar/non-polar amino acids. Additional analysis of many proteins indicated that almost all
proteins fall within the same range of having between 45
55% polar and 45
55% non-polar
e
e
amino acids.
The two basic types of classifiers are 'lumpers' and 'splitters.' Dividing the 20 common
amino acids into just two classes, non-polar and polar amino acids, is an example of lumping
( Table 6.1 ). There have been other systems that further sub-divide (splitting) the amino acids
into multiple classes. Table 6.2 presents a commonly used (splitter) system that is based on
the chemical structure of the side chains.
TABLE 6.2 A Classification System Based on the Chemical Structure of the Amino Acid Side Chains.
Polar
uncharged
Sulfur
containing
Aliphatic
Aromatic
Cation
Anion
Immino
Gly
Phe
Ser
Cys
Lys
Asp
Pro
Ala
Tyr
Thr
Met
His
Glu
Val
Trp
Asn
Arg
Leu
Gln
Ile
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