Problem 11 - Clinical Chemistry

Question

When a protein is dissolved in a buffer solution that is more alkaline than its \(\mathrm{pI}\) and an electric current is passed through the solution, the protein will act as: a. An anion and migrate to the anode b. A cation and migrate to the cathode c. An anion and migrate to the cathode d. An uncharged particle and will not move

Step-by-Step Solution

Answer

a. An anion and migrate to the anode

Step 1: Understanding \(\text{pI}\)

The \(\text{pI}\) or isoelectric point is the pH at which a protein carries no net charge. At this pH, the protein is neutral.

Step 2: Determine the Protein's Charge

When the pH of the buffer solution is more alkaline than the protein's \(\text{pI}\), the solution's pH is higher than the \(\text{pI}\), meaning the environment is more basic. In such conditions, the protein will lose protons (deprotonate) and carry a net negative charge, making it an anion.

Step 3: Analyzing the Protein's Motion

Since the protein is negatively charged (an anion) and an electric current is passed through the solution, it will migrate towards the positively charged electrode, which is the anode.

Step 4: Conclusion

Thus, when a protein is in a solution more alkaline than its \(\text{pI}\) and an electric current is applied, the protein acts as an anion and migrates to the anode.

Key Concepts

protein charge

Proteins, which are made up of amino acids, can carry different charges depending on the pH of their environment. Each amino acid has a side chain with either a positive, negative, or neutral charge. When many amino acids join together in a protein, the overall charge of that protein depends on the charges of its individual amino acids.

• At a high pH (alkaline), many of the amino acids lose protons, resulting in more negative charges.
• At a low pH (acidic), many amino acids gain protons, leading to more positive charges.

Because proteins can gain or lose protons, their charge will change. The point where a protein has no net charge is called the isoelectric point (pI). If the pH of the environment is higher than a protein's pI, the protein will generally become negatively charged (anionic). If it’s lower, the protein will generally become positively charged (cationic).

buffer solution pH

A buffer solution is a special solution that helps maintain a stable pH, even when small quantities of an acid or base are added. This is crucial for experiments involving proteins, as their function and charge can be greatly affected by pH.
Most buffer solutions are made of a weak acid and its conjugate base (or a weak base and its conjugate acid). They are designed to stabilize the pH within a narrow range.
When considering protein charge in a buffer solution, the pH of the buffer compared to the protein's pI becomes essential.

• If the buffer solution is more acidic (lower pH) than the protein's pI, the protein will be positively charged.
• If the buffer solution is more alkaline (higher pH) than the protein's pI, the protein will be negatively charged.

Therefore, to control the behavior of proteins in different experiments, scientists often choose an appropriate buffer solution with the desired pH.

electrophoresis

Electrophoresis is a technique used to separate molecules, like proteins, based on their size and charge. It works by applying an electric current across a gel or other medium through which the proteins move.

• Cathode: The negatively charged electrode (attracts cations).
• Anode: The positively charged electrode (attracts anions).

When a protein with a net negative charge (like one in a more alkaline buffer solution) is placed in the electrophoresis setup, it will migrate towards the anode because opposite charges attract. Conversely, positively charged proteins move towards the cathode.

While moving through the medium, proteins can also be separated by size. Smaller proteins generally move faster, allowing for detailed protein analysis. This technique is widely used in laboratory settings to study protein characteristics, identify proteins, and even in the preparation of purified proteins for further use in research.