Which of the following best describes a DNA molecule?
1. contains ribose ☐
2. double helix
3. made of amino acids
4. contains uracil
5. none of these
The Correct Answer and Explanation is :
The correct answer is:
2. double helix
Explanation:
A DNA (deoxyribonucleic acid) molecule is best described as a double helix. This refers to its three-dimensional structure, where two complementary strands of nucleotides are twisted around each other, resembling a twisted ladder.
The “rails” of this ladder are made up of a sugar-phosphate backbone, while the “rungs” consist of nitrogenous base pairs held together by hydrogen bonds. The bases pair specifically: adenine (A) with thymine (T), and cytosine (C) with guanine (G). This complementary pairing is essential for DNA’s role in genetic information storage and replication.
Why the other options are incorrect:
- Contains ribose:
DNA contains deoxyribose, not ribose. Ribose is the sugar found in RNA (ribonucleic acid). Deoxyribose differs from ribose because it lacks an oxygen atom on the second carbon. - Made of amino acids:
DNA is not made of amino acids. Instead, it is composed of nucleotides, which consist of a sugar (deoxyribose), a phosphate group, and a nitrogenous base. Amino acids, on the other hand, are the building blocks of proteins, not nucleic acids. - Contains uracil:
DNA does not contain uracil; it uses thymine as one of its nitrogenous bases. Uracil is found in RNA, where it replaces thymine and pairs with adenine. - None of these:
This option is incorrect because the double helix is a defining characteristic of DNA.
DNA’s structure enables it to serve as the blueprint for life, directing protein synthesis and carrying genetic information across generations. The double helix structure also allows for accurate replication and repair, which is critical for maintaining genetic stability.