Problem 22 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Following two amino acids lysine and glutamine form dipeptide linkage. What are two possible dipeptides?

Step-by-Step Solution

Answer

Lysylglutamine and glutamyllysine are the two possible dipeptides.

Step 1: Understand Dipeptide Formation

A dipeptide is formed when two amino acids are joined by a peptide bond. This bond occurs between the carboxyl group of one amino acid and the amino group of another, with the release of a water molecule (condensation reaction).

Step 2: Identify the Amino Acids Involved

The exercise involves two amino acids: lysine and glutamine. With these two, we can form different combinations by deciding which amino acid will be at the N-terminus (start) and which will be at the C-terminus (end).

Step 3: Determine the First Dipeptide

When lysine is at the N-terminus and glutamine at the C-terminus, the dipeptide formed is known as lysylglutamine. This means lysine's carboxyl group forms a bond with glutamine's amino group.

Step 4: Determine the Second Dipeptide

Alternatively, when glutamine is at the N-terminus and lysine at the C-terminus, the dipeptide formed is glutamyllysine. This structure has glutamine's carboxyl group forming a bond with lysine's amino group.

Step 5: Summarize the Possible Dipeptides

The two possible dipeptides that can form from lysine and glutamine are lysylglutamine and glutamyllysine. These differ based on the order of the amino acids.

Key Concepts

Amino Acids

Amino acids are the building blocks of proteins. Each amino acid contains an amino group \(\text{-NH}_2\), a carboxyl group \(\text{-COOH}\), and a unique side chain which determines its properties.
Amino acids are connected in varied sequences to form proteins, essential molecules in biochemistry.
This is analogous to how letters are used to form words and sentences.
- Essential for growth and repair of tissues
- Can be classified based on their side chain properties (e.g., polar, non-polar, acidic, or basic)
- Each one plays distinct roles in metabolism and body function

Lysine and Glutamine, the amino acids in the given exercise, are joined to form dipeptides. Lysine is known for its basic properties due to its side chain, while glutamine is neutral and plays a role in nitrogen metabolism.

Peptide Bond

A peptide bond is a special link that forms between amino acids. This bond is a strong covalent bond that connects the carboxyl group of one amino acid to the amino group of another.
This bond is crucial in forming proteins, as it creates the long chains of linked amino acids known as polypeptides.
Without peptide bonds, proteins could not form and function properly.
- Provides proteins their structure by linking amino acids in a specific sequence
- Is very stable, which is critical for maintaining protein integrity

In the formation of a dipeptide from lysine and glutamine, a peptide bond allows the molecules to join, creating either lysylglutamine or glutamyllysine.

Condensation Reaction

A condensation reaction is a chemical process by which two molecules are joined, releasing a molecule of water in the process.
This happens when one molecule loses a hydrogen atom from an amino group, and another loses a hydroxyl group from a carboxyl group, allowing them to bond.
The combination of two amino acids through a condensation reaction forms a dipeptide.
- Important in biological systems for forming complex molecules
- Removes a water molecule as a by-product

During the dipeptide formation of lysine and glutamine, the condensation reaction is what facilitates the creation of the peptide bond, transforming these separate amino acids into a connected peptide structure.