The amine group has a neutral charge leaving only a negative charge on the carboxylate group. Look at the side chain to identify the amino acid. The pI values for amino acids are found in the table of amino acids. Allison Soult , Ph. Department of Chemistry, University of Kentucky. Learning Outcomes Identify structural components of an amino acid.
Define zwitterion and isoelectric point. Determine the charge on an amino acid when it is not at the isoelectric point. Label amino acids as polar and nonpolar and as acidic, basic, or neutral. Amino acids can be shown with or without charges.
These are equivalent structures. Alanine's side chain is nonpolar, while threonine's is polar. Tryptophan is one of several amino acids whose side chain is aromatic. Aspartic acid has an acidic side chain, while lysine has a basic side chain. Rules for classifying amino acids The following rules along with two exceptions can help you classify amino acids as nonpolar, polar acidic sometimes called acidic , polar basic sometimes called basic , or polar neutral.
Nonpolar amino acids there are 9 contain aliphatic hydrocarbon chains or aromatic rings. Polar acidic amino acids 2 contain a carboxylic acid or carboxylate group in the side chain R group.
This is in addition to the one in the backbone of the amino acid. Polar basic amino acids 3 contain an amine may be neutral or charged group in the side chain R group. Polar neutral amino acids 6 contain a hydroxyl -OH , sulfur, or amide in the R group. There are two important exceptions to the above rules. Tyrosine has an aromatic group and an -OH group and is considered polar neutral. Methionine contains a sulfur but as a part of carbon chain.
Sulfur has the same electronegativity as carbon, so it is considered nonpolar. Zwitterion Amino acids are typically drawn either with no charges or with a plus and minus charge see figure In gel electrophoresis, the molecules to be separated are pushed by an electrical field through a gel that contains small pores.
The molecules travel through the pores in the gel at a speed that is inversely related to their lengths. As previously mentioned, gel electrophoresis involves an electrical field; in particular, this field is applied such that one end of the gel has a positive charge and the other end has a negative charge. Because DNA and RNA are negatively charged molecules, they will be pulled toward the positively charged end of the gel. Proteins, however, are not negatively charged; thus, when researchers want to separate proteins using gel electrophoresis, they must first mix the proteins with a detergent called sodium dodecyl sulfate.
This treatment makes the proteins unfold into a linear shape and coats them with a negative charge, which allows them to migrate toward the positive end of the gel and be separated. Finally, after the DNA, RNA, or protein molecules have been separated using gel electrophoresis, bands representing molecules of different sizes can be detected. Related Concepts
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