Understanding Basic Groups in Lysine

Lysine is an amino acid with the chemical formula C₆H₁₄N₂O₂. It contains an amino group (-NH₂) and a carboxylic acid group (-COOH) attached to the alpha carbon, along with an additional amino group on its side chain. A basic group is one that can accept a proton (H⁺). In organic chemistry, amino groups (-NH₂) are basic because the nitrogen atom has a lone pair that can accept a proton.

Step 1: Identify the Structure

The given structure of lysine (in the image) is:

H₂N-CH₂-CH₂-CH₂-CH₂-CH(NH₂)-COOH

This shows lysine in its neutral form, with two amino groups: one at the alpha position (attached to the carbon next to COOH) and one at the end of the side chain.

Step 2: Locate Basic Groups

Basic groups in amino acids are typically amino groups (-NH₂). In lysine:

• The alpha-amino group (-NH₂ attached to the alpha carbon) is basic.
• The side chain amino group (-NH₂ at the end of the chain) is also basic.

Note: The carboxylic acid group (-COOH) is acidic, not basic.

Step 3: Count the Basic Groups

Lysine has two amino groups, both of which are basic. Therefore, the total number of basic groups is 2.

Final Answer

The total number of basic groups in the given form of lysine is $2$.

Related Topics

• Amino Acids: Building blocks of proteins, each with an amino group, a carboxyl group, and a unique side chain.
• Acid-Base Properties: Amino acids can act as both acids and bases (amphoteric). The pKa values determine protonation states.
• Isoelectric Point (pI): The pH at which an amino acid has no net charge. For lysine, pI is around 9.7 due to its basic side chain.

Important Formulae and Theory

Basic Group Definition: A group that can accept a proton (Bronsted-Lowry base). For amino acids, amino groups (-NH₂) are basic:

pKa and Protonation: The pKa indicates the pH where half the group is protonated. Amino groups typically have pKa values between 9 and 10.

Lysine Structure: Chemical formula: $C_6{H}_{14}{N}_2{O}_2$. It is classified as a basic amino acid due to its extra amino group.