Which of the following best describes a DNA molecule? A double helix that c
The Correct Answer and Explanation is:
The correct answer is “double helix.”
A DNA molecule is best described as a double helix, a term that captures the elegant, spiral structure of its two intertwined strands. This shape resembles a twisted ladder, with the sugar-phosphate backbones forming the sides and paired nitrogenous bases creating the rungs. The strands run in opposite directions and are held together by hydrogen bonds between specific base pairs: adenine pairs with thymine, and cytosine pairs with guanine.
Each DNA strand is composed of repeating units called nucleotides. A nucleotide consists of three components: a phosphate group, a five-carbon sugar called deoxyribose, and one of four nitrogen-containing bases (adenine, thymine, cytosine, or guanine). The order of these bases encodes genetic information, much like letters in a language.
The double helix structure is not just visually distinctive; it is also functionally significant. The complementary nature of the base pairs enables DNA replication. When a cell prepares to divide, the two strands of the helix separate, and each serves as a template for building a new complementary strand. This ensures that genetic information is accurately passed on to daughter cells.
The other choices in the question are inaccurate descriptions of DNA. DNA contains deoxyribose, not ribose; ribose is found in RNA. DNA is not made of amino acids—those are the building blocks of proteins. Lastly, uracil is found in RNA, where it replaces thymine. DNA uses thymine exclusively.
Understanding the double helix structure was a turning point in biology. It revealed how genetic instructions are stored, replicated, and passed from generation to generation, laying the foundation for molecular genetics, biotechnology, and modern medicine.
