What macromolecule do viroids consist of?

Viroids are unique infectious agents that are primarily composed of a small, circular strand of RNA. Unlike viruses, which typically consist of nucleic acids surrounded by a protein coat, viroids lack any protein-coding capability and do not contain a protective protein layer. This RNA is capable of self-replication and can interfere with the normal functioning of the host plant's cellular machinery, leading to various diseases.

The structure of viroids is crucial to their mode of action. The small size and circulatory nature of the RNA allow them to adopt specific shapes that can facilitate their interaction with plant RNA-dependent RNA polymerases. This interaction is a key factor in their ability to propagate within host plants.

In contrast, the other macromolecules listed—proteins, DNA, and lipids—do not characterize viroids. Proteins are typically found in viruses but are absent in viroids. DNA is a different type of nucleic acid that is not present in viroid structure. Lipids, while important in the structure of many viruses as they help form the viral envelope, do not play a role in viroids, as viroids do not have a lipid membrane or any lipid components.

Thus, the correct identification of viroids being composed of RNA aligns