Deoxyribonucleic acid (DNA) is the carrier of genetic information and the main constituent of chromosomes in nearly all living organisms. Which molecule is this?

• A. RNA
• B. DNA
• C. Proteins
• D. Carbohydrates

Answer: (B)

The molecule that stores genetic information and forms the chromosomes in nearly all living organisms is DNA. Its genetic information is encoded in the sequence of nucleotides, and this sequence is faithfully copied during cell division, allowing inheritance from one generation to the next. DNA normally exists as a double helix, with a sugar-phosphate backbone and bases pairing specifically (adenine with thymine, cytosine with guanine), a arrangement that supports accurate replication and repair.

In chromosomes, DNA is packaged with proteins to form chromatin, which enables the long DNA molecule to fit inside the cell nucleus while still being accessible for transcription and replication. The other molecules listed—RNA, proteins, and carbohydrates—play essential roles in cells, but they do not serve as the primary hereditary material or the main constituent of chromosomes. RNA participates in gene expression and can store genetic information in some viruses, proteins perform cellular functions, and carbohydrates are primarily energy sources or structural components. DNA uniquely satisfies both criteria: carrying genetic information and making up chromosomes in almost all organisms.