Howdy,
I need suggestion on this question.
You spotted a mixture of Ala, Arg, Asp, Glu, His, and Lys on an isoelectric focusing where the left and right sides have pH 2 and 13, respectively. After a while, all amino acids stop migration on the strip. Answer an amino acid (in three-letter code) whose band shows up the third from the left (i.e., lower pH).
Hint: you need to calculate their pI based on the pKa value, pK1 (i.e., pKa of COOH) and pK2 (i.e., pKa of NH3+).
So I evaluated using the pI of the amino acids from a standard table because when I tried calculating pI for some amino acids using the pka of NH3+ and COO- it didn’t match the standard table . And I got Ala ( alanine ) to be the third AA. Is there a mistake?
Thanks!
To determine the amino acid that shows up third from the left on the isoelectric focusing strip, we need to calculate the isoelectric point (pI) for each amino acid.
The pI is the pH at which an amino acid has no net charge. It can be calculated using the pKa values of the carboxyl group (pKa1) and the amino group (pKa2). The pI is the average of these two pKa values.
For example, let's calculate the pI for Ala (alanine):
The pKa values for Ala are approximately 2.34 (pKa1 for COOH) and 9.69 (pKa2 for NH3+).
The pI can be calculated using the formula: pI = (pKa1 + pKa2) / 2
pI for Ala = (2.34 + 9.69) / 2 = 6.02
Now, let's calculate the pI for the other amino acids you mentioned (Arg, Asp, Glu, His, and Lys) using the same method.
- Arginine (Arg):
pKa1 = 2.17
pKa2 = 9.04
pI = (2.17 + 9.04) / 2 = 5.60
- Aspartic acid (Asp):
pKa1 = 1.88
pKa2 = 9.60
pI = (1.88 + 9.60) / 2 = 5.74
- Glutamic acid (Glu):
pKa1 = 2.19
pKa2 = 9.67
pI = (2.19 + 9.67) / 2 = 5.93
- Histidine (His):
pKa1 = 1.82
pKa2 = 9.17
pI = (1.82 + 9.17) / 2 = 5.50
- Lysine (Lys):
pKa1 = 2.16
pKa2 = 9.06
pI = (2.16 + 9.06) / 2 = 5.61
Now, we can compare the pI values of these amino acids to determine which one will be the third from the left on the isoelectric focusing strip.
From the pI values calculated above, the amino acid with the third lowest pI is His (Histidine) with a pI of 5.50. Therefore, His (Histidine) is the amino acid that shows up third from the left (at a lower pH) on the isoelectric focusing strip.
Let me know if you need any further assistance!
To determine the amino acid that shows up third from the left on the isoelectric focusing, you need to calculate the isoelectric point (pI) for each amino acid and compare them. The pI is the pH at which the molecule carries no net electrical charge. The formula for calculating pI depends on the pKa values of the ionizable groups in the amino acid.
To calculate the pI of an amino acid:
1. Determine the pKa values for the acidic (COOH) and basic (NH3+) side chains for each amino acid. For example, the pKa values for Ala (alanine) are pK1 (COOH) = 2.34 and pK2 (NH3+) = 9.69.
2. Calculate the average of these pKa values: (pK1 + pK2) / 2.
3. The pI for the amino acid is the average of the pKa values.
Now, let's calculate the pI for the amino acids you mentioned:
- Ala (alanine): pI = (2.34 + 9.69) / 2 = 6.02
- Arg (arginine): pI = (2.17 + 9.04) / 2 = 5.61
- Asp (aspartic acid): pI = (1.88 + 9.60) / 2 = 5.74
- Glu (glutamic acid): pI = (2.19 + 9.67) / 2 = 5.93
- His (histidine): pI = (1.82 + 9.17) / 2 = 5.50
- Lys (lysine): pI = (2.16 + 8.95) / 2 = 5.56
From these calculations, it appears that the amino acid with the third lowest pI is His (histidine), not Ala (alanine). Therefore, the three-letter code for the amino acid that shows up third from the left on the isoelectric focusing is His.
It's important to note that the pKa values used for calculation may vary slightly depending on the source, so there can be some discrepancies between calculated and table values. However, the calculation method described above should provide a reasonable approximation for identifying the amino acid in question.