**Question:** Which of these amino acids will migrate slowest to the anode end at the physiological pH?

A. Arginine
B. Glutamic acid
C. Histidine
D. Serine

**Core Concept:**
The migration of amino acids in an electric field is based on their isoelectric points (pI), which are the pH values at which the net charge of the molecule is zero. Amino acids with different pI values will migrate at different rates as they pass through a capillary electrophoresis system.

**Why the Correct Answer is Right:**
At physiological pH (around 7.4), the amino acids will be charged or neutral due to their protonation or deprotonation states. Among the given options, Arginine (pI = 9.7) will have the highest positive charge at physiological pH, making it the slowest to migrate to the anode end.

**Why Each Wrong Option is Incorrect:**
1. Glutamic acid (pI = 4.2) has a lower pI, resulting in faster migration compared to Arginine.
2. Histidine (pI = 6.0) has a higher pI than Glutamic acid, but not as high as Arginine, so it migrates faster than Arginine but slower than Glutamic acid.
3. Serine (pI = 9.7) has a similar pI to Arginine, but Arginine's positive charge contributes to slower migration compared to Serine's neutral amino acid.

**Clinical Pearl:**
Understanding amino acid migration patterns in capillary electrophoresis is essential for various applications, including protein and peptide analysis in clinical, forensic, and food science fields. In these fields, accurate detection and identification of amino acids are crucial for diagnostics, drug development, and quality control.

**Correct Answer:** D. Serine

Amino acids with different pI values will migrate at different rates in capillary electrophoresis, which is useful for various applications, including protein and peptide analysis in clinical, forensic, and food science fields. In these fields, accurate detection and identification of amino acids are crucial for diagnostics, drug development, and quality control. Serine has a pI of 9.7, which is similar to Arginine (9.7). However, Arginine's positive charge contributes to slower migration compared to Serine's neutral amino acid.