Question

At iso-electric point, (A) Concentration of cation is equal to concentration of anion (B) Net charge is zero (C) No movement of amino acid under the influence of electric field. (D) All of the above

Short answer

The correct answer is (D) All of the above, as all statements accurately describe the properties of an amino acid at its iso-electric point: (A) concentration of cation is equal to concentration of anion, (B) net charge is zero, and (C) no movement of amino acid under the influence of the electric field.

Step-by-step solution

Analyzing statement A

(A) Concentration of cation is equal to concentration of anion At the iso-electric point, the amino acid exists predominantly in its zwitterionic form. A zwitterion is a molecule with both positive and negative charges, but with a net charge of zero. At this point, the concentration of cations and anions is equal. So, statement A is correct.

Analyzing statement B

(B) Net charge is zero As mentioned earlier, at the iso-electric point, amino acid molecules predominantly exist in their zwitterionic form. Since the positive and negative charges cancel each other out, the net charge on the molecule is zero. Therefore, statement B is correct.

Analyzing statement C

(C) No movement of amino acid under the influence of an electric field. At its iso-electric point, an amino acid carries no net charge, which means it won't be attracted to either the positive or negative electrode when placed in an electric field. Thus, the amino acid will not move under the influence of the electric field. Statement C is correct.

Analyzing statement D

(D) All of the above Since we found that all the statements (A, B, and C) are correct, statement D is also correct. All the given statements accurately describe the properties of an amino acid at its iso-electric point. Thus, the correct answer is (D) All of the above.

Key concepts

Zwitterions

Zwitterions are fascinating molecules, particularly prevalent in the study of biochemistry. Think of a zwitterion as a chemical chameleon, able to sport both a positive and a negative charge simultaneously. In the context of amino acids, which are the building blocks of proteins, zwitterions are crucial for understanding how these molecules behave in different environments.

Structurally, an amino acid zwitterion contains both an ammonium group (\(NH_3^+\)) and a carboxylate group (\(COO^-\)), which account for the positive and negative charges, respectively. Notably, this dipolar ionic state predominates at a specific pH known as the iso-electric point, where the molecule's net charge is zero.

• Amino acids in their zwitterionic form exhibit unique solubility and reactivity traits.
• At the iso-electric point, the positive and negative charges within the zwitterions cancel out, leading to no net charge.
• The equilibrium between the zwitterionic and the non-zwitterionic forms is pH-dependent, with the zwitterionic form being favored at the iso-electric point.

Amino Acids

Amino acids serve as the fundamental units from which proteins are synthesized. They hold central roles in both the structure and function of all living organisms. Each amino acid features a primary amine (\(NH_2\)) group, a carboxylic acid (\(COOH\)) group, and a unique side chain or R group that distinguishes one amino acid from another.

The chemistry of amino acids is governed by the ionizable nature of the amine and carboxyl groups, which can accept or donate protons based on the pH of their environment. Thus, each amino acid has a characteristic iso-electric point where the molecule does not carry a net charge.

• In organisms, amino acids are linked together by peptide bonds forming polypeptides or proteins.
• Amino acids can undergo ionization, where they can function as either acids or bases.
• The unique R group influences an amino acid's properties, including its iso-electric point.

Electric Field Influence on Amino Acids

The behavior of amino acids under the influence of an electric field is an essential concept in biochemistry, particularly in techniques like electrophoresis. In an electric field, ions migrate towards the electrode with the opposite charge. Amino acids, when charged, will thus move towards either the anode or cathode based on whether they are negatively or positively charged.

However, at an amino acid's iso-electric point, the overall movement is halted because the amino acid is in its zwitterionic form with a net charge of zero. This iso-electric focusing is a powerful method to separate and analyze proteins and amino acids with high precision.

• Amino acids will migrate in an electric field depending on their charge state, moving towards opposite charges.
• At the iso-electric point, amino acids do not migrate because they carry no net charge.
• Understanding this principle is valuable for techniques such as isoelectric focusing, which separates molecules based on their iso-electric points.