Question 10

Proteins contain both an amine and a carboxyl group.

Proteins are unique among organic molecules because they consist of amino acids, which inherently contain both an amine group (-NH2) and a carboxyl group (-COOH). This structural characteristic is fundamental to their function and classification as proteins.

A) Lipids

Lipids do not contain both an amine and a carboxyl group; they are primarily composed of fatty acids and glycerol. While some lipids may have functional groups, they lack the specific combination of an amine and a carboxyl group that defines proteins.

B) Cellulose

Cellulose is a polysaccharide made up of glucose units linked by glycosidic bonds. It does not contain an amine group, and its structure is entirely different from that of proteins, which include both amine and carboxyl groups.

C) Chitin

Chitin is a structural polysaccharide found in the exoskeletons of arthropods and the cell walls of fungi. Although it contains nitrogen, it does not possess both an amine and a carboxyl group as part of its structural framework, making it distinct from proteins.

D) Proteins

Proteins are composed of amino acids, each of which features an amine group and a carboxyl group. This dual presence is essential for protein synthesis and function, distinguishing proteins from other organic molecules.

Conclusion

Proteins stand out as the only organic molecules listed that contain both an amine and a carboxyl group, a characteristic that is vital for their biological roles. In contrast, lipids, cellulose, and chitin lack this specific structural feature, confirming that D is the only correct answer.