Question

Paper electrophoresis at \(\mathrm{pH} 6.0\) was carried out on a mixture of glycine, alanine, glutamic acid, lysine, arginine and serine, (a) Which compound moved toward the anode? (b) Which moved toward the cathode? (c) Which remained at the origin?

Short answer

(a) At pH 6.0, Glycine, Glutamic acid, and Serine have negative charges and moved toward the anode. (b) At pH 6.0, Alanine, Lysine, and Arginine have positive charges and moved toward the cathode. (c) No amino acids had a neutral charge at pH 6.0, so none remained at the origin during the paper electrophoresis.

Step-by-step solution

Understand the charges of amino acids

At pH 6.0, we need to determine the charge of each amino acid. Amino acids can have positive, negative, or neutral charges. For this, we must know the isoelectric points (pI) of each amino acid. The isoelectric point is the pH at which an amino acid has a neutral charge. If the pH is lower than the pI, the amino acid will have a positive charge. If the pH is higher than the pI, the amino acid will have a negative charge. Here are the isoelectric points for the given amino acids: - Glycine (pI = 5.97) - Alanine (pI = 6.11) - Glutamic acid (pI = 3.22) - Lysine (pI = 9.74) - Arginine (pI = 10.76) - Serine (pI = 5.68)

Determine the amino acids with negative charges

Now, we will determine which amino acids have negative charges at pH 6.0. If the pH (6.0) is higher than the pI, then the amino acid has a negative charge. - Glycine: pH 6.0 > pI 5.97 - Glutamic acid: pH 6.0 > pI 3.22 - Serine: pH 6.0 > pI 5.68 So, Glycine, Glutamic acid, and Serine have negative charges. (a) Since anode attracts negatively charged particles, the compounds that moved towards the anode are Glycine, Glutamic acid, Serine.

Determine the amino acids with positive charges

Now, we will determine which amino acids have positive charges at pH 6.0. If the pH (6.0) is lower than the pI, then the amino acid has a positive charge. - Alanine: pH 6.0 < pI 6.11 - Lysine: pH 6.0 < pI 9.74 - Arginine: pH 6.0 < pI 10.76 So, Alanine, Lysine, and Arginine have positive charges. (b) Since cathode attracts positively charged particles, the compounds that moved towards the cathode are Alanine, Lysine, Arginine.

Determine the amino acids with neutral charges

To find which amino acid remained at the origin, we need to check if there is any amino acid with a neutral charge at pH 6.0. None of the given amino acids have a pI equal to 6.0. (c) There are no amino acids with a neutral charge, so none remained at the origin during the paper electrophoresis.

Key concepts

Amino Acid Charge at Specific pH

Understanding the charge of amino acids at a given pH is essential for techniques like paper electrophoresis. Amino acids can either be positively charged, negatively charged, or neutral, dependent on the solution's pH. In this context, the specific pH is compared to each amino acid's isoelectric point (pI).
- If the pH is less than the pI, the amino acid carries a positive charge. This is because the environment is more acidic, leading to gaining protons. - If the pH is greater than the pI, the amino acid has a negative charge. This means the environment is more basic, causing the release of protons.
This behavior underlines why different amino acids will move differently under an electric field during electrophoresis.

Isoelectric Point of Amino Acids

The isoelectric point (pI) of an amino acid is the pH at which the amino acid has no net electrical charge. At this point, the positive and negative charges within the amino acid balance each other out. It is a critical factor in determining how an amino acid will react in various environments, especially in electrophoresis.
For instance:

• Glycine has a pI of 5.97, closely aligning with neutral conditions.
• Glutamic acid, with a pI of 3.22, tends to be negatively charged in neutral or slightly basic environments due to its lower pI.
• Lysine, possessing a higher pI of 9.74, requires an alkaline setting to reach a neutral charge.

Knowing these pI values allows scientists to predict how amino acids will move when subjected to an electric field at a certain pH.

Anode and Cathode Attraction

In electrophoresis, separation of molecules occurs based on their charges. Positively charged particles are attracted to the negatively charged cathode, while negatively charged particles move towards the positively charged anode. This process capitalizes on the basic principle that opposite charges attract.
- The anode attracts negatively charged amino acids like glycine, glutamic acid, and serine at pH 6.0. - Conversely, the cathode pulls amino acids with a charge such as alanine, lysine, and arginine towards it.
This movement aids in the separation of molecules, allowing researchers to analyze or purify specific compounds within a mixture.

pH and Amino Acid Charge Relation

The relationship between pH and the charge of amino acids is pivotal in biochemistry. Amino acids have two main forms: a positively charged form and a negatively charged form. The pH of the environment triggers a shift between these forms.
- At low pH, amino acids gain extra protons and often become positively charged - At high pH, amino acids lose protons, acquiring a negative charge instead
Amino acids interact with environmental pH in a way that influences their charge. Understanding this interaction is essential for applications like electrophoresis, where the migration of amino acids depends on their charge, thus their surrounding pH. It allows for fine control and separation of compounds based on how they respond to electric fields within different pH environments.