acidity/basicity of amino acids

[jones106]

How can you tell if a given amino acid is acidic or basic? I'm lost here. My first thought would be to look at the pKa values. There is virtually no difference in the pKa values for the carboxyl groups; all range from 1.82-2.38. The same goes for the pKa values of the amino groups; all range from 8.8-10.96. Is it the pKa of the R group that determines whether they are acidic or basic? My brain hurts

Thanks very much,
Taylor

[sxdxland]

amino acid is ambisexuality .
when the pH>PI(the amino acid),it's basic,and when pH<PI,it's acidic,

if you have some problem about amino acid
you can give a email (anysa@126.com)

[littlesti]

I disagree with above- look at the PI- if PI (isoelectric point) is lower than 7, it is acidic and vv.

[feniouk]

Your last guess is right: the pK of the side chain is the only thing that matters. That makes Glu+Asp acid, and Lys+Arg basic.

Regards,

Boris.

[John Ellis]

dont u look at the structure? for example the aspartic and glutamic acids are confirmed acids as they are dicarboxylic i.e. one extra carboxylic group while the basic amino acids have one extra amino group, lysine ,etc.

[agador]

Given that all amino acids contain both an basic (amine group) and an acidic group they all are amphoteric (a chemical species acting as both an acid and a base). However when an instructor or textbook categorizes aa's ie polar vs. non polar, acid vs. bases, etc. they are referring to the functional groups of the R chains

Therefore glutamine (amide R group) is a non-charged (ie it does not posses physiologically relevant ionization/acid-base character), polar <-->hydrophillic aa
glutamate is a chargable (a/b character from carboxyl R group) aa

In short ALL amino acids are both acids and bases
Categorization of amino acids is dependent on the functional groups contained in the R group.

PS
pKa values given for the ionization of certain aa functional groups are often determined for that amino acid in isolation. Interactions between different aa in a polypeptide may be produce significantly altered pKa values from their quoted value

[priji]

Amino acids are crystalline solids with relatively high melting points, and most are quite soluble in water and insoluble in non-polar solvents.