Hemoglobins from two individuals are compared by electrophoresis and by fingerprinting. Electrophoresis reveals no difference in migration, but fingerprinting shows an amino acid difference. How is this possible?

Electrophoresis is a method used to separate proteins based on their size and charge. The proteins are placed in a gel and an electric field is applied, causing the proteins to migrate through the gel. Positively charged proteins will migrate towards the negative electrode (cathode), while negatively charged proteins will migrate towards the positive electrode (anode). The rate of migration is influenced by the size and the charge of the protein.

Fingerprinting, also known as peptide mapping, is a technique used to identify the specific amino acid sequence of a protein. In this technique, proteins are first digested with protease enzymes (such as trypsin) to generate smaller peptides. The resulting peptide fragments are then separated using techniques like high-performance liquid chromatography (HPLC) or mass spectrometry (MS). The peptide fragments can be analyzed to determine the amino acid sequence of the original protein, which allows for the identification of any amino acid differences between two proteins.

Electrophoresis primarily detects differences in size and charge of proteins. Therefore, if two proteins have the same size and net charge, they will migrate at the same rate in the gel, and no difference will be observed by electrophoresis. However, this does not mean that there are no differences in their amino acid sequence. Fingerprinting, on the other hand, detects differences at the amino acid sequence level. Even if the size or charge of two proteins is the same, a single amino acid difference between them can be detected by fingerprinting.

The scenario in this exercise presents a case where electrophoresis did not detect any difference between the hemoglobins from two individuals, but fingerprinting showed an amino acid difference. This could be explained as follows: 1. The hemoglobins from both individuals may have a similar size and net charge, causing them to migrate at the same rate during electrophoresis, which gives a false impression that they are identical. 2. However, the fingerprinting technique, which analyzes the amino acid sequence at a much detailed level, detected a difference in the amino acid sequence of the hemoglobins. This means that indeed there is a difference between the hemoglobins of the two individuals, despite the electrophoresis results. In conclusion, the fingerprinting technique is more sensitive to differences in protein sequences and provides a more accurate assessment of the similarities and differences between the hemoglobins of the two individuals.