Which of the following is basic amino acid

General
1

which of the following is basic amino acid

2

Which of the following is a basic amino acid?

Answer:
In biochemistry, amino acids are classified based on the nature of their side chains. Basic amino acids are those that have side chains with a positive charge at physiological pH. The basic amino acids have side chains that consist of a basic group, such as an amine.

The three standard basic amino acids are:

  1. Lysine (Lys, K):

    • Lysine has a side chain with an aliphatic hydrocarbon tail that ends with an amine group.

      \text{Lysine Structure: H}_2\text{N-CH(CH}_2\text{CH}_2\text{CH}_2\text{NH}_2\text{)-COOH}

  2. Arginine (Arg, R):

    • Arginine has a side chain containing three carbon atoms followed by a guanidino group, which has a high pKa, making it very basic.

      \text{Arginine Structure: H}_2\text{N-C(NH)-NH-(CH}_2\text{)_3-CH(NH}_2\text{)-COOH}

  3. Histidine (His, H):

    • Histidine’s side chain contains an imidazole ring, which can gain a proton, making it basic.

      \text{Histidine Structure: H}_2\text{N-CH-CH(NH}_2\text{)-COOH}

In the context of multiple-choice questions, ensure you select any of these three amino acids if they appear among the options given. Here is a brief recap of their characteristics:

1. Basic Amino Acids:

  • Lysine (Lys, K): Contains an \epsilon-amino group, making its side chain basic.
  • Arginine (Arg, R): Contains a guanidino group, highly basic with a very high pKa (~12.5).
  • Histidine (His, H): Contains an imidazole ring, which can act as a proton acceptor at physiological pH due to its pKa (~6.0).

Therefore, if you are given a list of amino acids and asked to identify the basic one, look for lysine, arginine, or histidine.