This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. The N-terminal amino acid of a peptide can be determined by reaction with (a) Hydrazine (b) 2, 4 -dinitrophenyl hydrazine (c) 2,4 -dinitrofluorobenzene (d) Acetic anhydride

Peptide analysis is a critical aspect of biochemical research, particularly in understanding protein structure and function. It involves a variety of techniques aimed at determining the composition and sequence of amino acids in a peptide chain.

For students embarking on peptide analysis, accurate identification of the N-terminus, the starting point of a peptide chain, is essential. Utilizing different reagents and methodologies, researchers can identify the sequence of amino acids. Chromatography and mass spectrometry are commonly employed techniques following chemical reactions that label the amino acids, enabling their separation and identification.

Understanding the specific role of reagents in peptide analysis is crucial. It allows researchers to make informed decisions when designing experiments for protein characterization. As students tackle these concepts, emphasising the importance of the N-terminal identification is vital as it provides a starting point for sequential analysis and often contains reactive sites that are important for protein's function or interactions.

Sanger's reagent, named after the Nobel Prize-winning scientist Frederick Sanger, is a pivotal chemical in protein chemistry. It's specifically designed to label the N-terminus of a peptide, which is the first amino acid in a protein or peptide chain.

This reagent works by selectively reacting with the free amino group that only the N-terminal amino acid possesses. Upon reacting with Sanger's reagent, the amino acid becomes a 'tagged' derivative which can be easily detected through chromatographic techniques. For students, recognizing the importance of Sanger's method allows for a greater understanding of protein sequencing and the historical development of biochemistry. Sanger's pioneering work not only made it possible to determine protein sequences but also laid the groundwork for DNA sequencing technologies.

Moreover, understanding Sanger's reagent highlights the interplay between chemical reactivity and biological specificity, a fundamental concept in a biochemistry learner's journey.

2,4-Dinitrofluorobenzene (DNFB) is the chemical compound behind Sanger's reagent. It's characterized by a benzene ring substituted with two nitro groups and a fluorine atom. The reactivity of DNFB, particularly with amino groups, makes it ideal for tagging the N-terminal amino acid.

The reaction involves the amino group displacing the fluorine atom, creating a stable dinitrophenyl-amino acid derivative. This chemical linking process is non-destructive to other amino acids in the chain, making it a specific labelling method for the N-terminal amino acid.

For students learning about peptide analysis, grasping the reactivity of DNFB and its specificity is essential. Acknowledging these details can empower students to understand more sophisticated analytical techniques such as mass spectrometry, where such tagged peptides can be uniquely identified. It also illustrates the utility of chemistry in bioanalytical applications, turning simple compounds into powerful tools for scientific exploration.