Question

Although amino acids have "acid" in their name, some are acidic in water solutions, some are basic, and other are neutral. Propose an explanation for this observation

Answer 1

I believe the correct answer is that the amide group is acidic.

Explanation:

An acid is a proton donor. An amino acid has 3 parts i.e. the amide end, the R prosthetic group and the carboxilic end. When a protein is being formed, attachment of compounds on the R group will cause the amide group to donate an ion that the carboxilic end picks up or sometimes it does not. The amide end of the amino acid that has lost the hydrogen ion will bind to the carboxilic end of another amino acid meanin that if you are forming  long chain of a protein, only one hydrogen donated by the amide end will bind to the only 1 carboxilic end tail of the protein. All the hydrogens donated by the amide ends of the amino acids forming the protieins are the ones that will influence the pH of the amino acid in water. Simple amino acids will just have one hydrogen atom on the R-group of the amino acid and since they are not binding to any other amino acids, they do not lose their one hydrogen on their amide end to the carboxilic end. An example is glycine. The R-group also can determine their pH depending on the number of hydrogen atoms that they can produce.

Some amino acids have acidic prosthetic groups that influence their pH much more further. The amino acids that are found in the human body are 20 in number with structures ranging in complexity. They are assigned names and abbreviations that sometimes does not represent any letter in their naming. The amino acids are: alanine - ala - A (gif, interactive)  

arginine - arg - R  

asparagine - asn - N  

aspartic acid - asp - D  

cysteine - cys - C

glutamine - gln - Q  

glutamic acid - glu - E

glycine - gly - G  

histidine - his - H  

isoleucine - ile - I  

leucine - leu - L  

lysine - lys - K  

methionine - met - M  

phenylalanine - phe - F  

proline - pro - P  

serine - ser - S  

threonine - thr - T  

tryptophan - trp - W  

tyrosine - tyr - Y

valine - val - V

Level: College

Subject: Biochemistry

Topic: Amino Acids

Answer 2

The pH of an amino acid is determined by the nature of the side chains of that amino acid. If the side chain of an amino acid contains amine functional group the amino acid will be basic. The acidic amino acids are acidic because they have carboxylic acid functional groups at their side chain.