Question

Which of the following statements is wrong for viroid?
A. They lack a protein coat.
B. They are smaller than viruses
C. They cause infections
D. Their RNA is of high molecular weight

Answer 1

Viroid is basically a plant pathogen that consists of a short stretch of highly complementary, circular single stranded RNA. The size of the viroid ranges from 246 to 247 nucleotides. They are responsible for causing disease in plants like potato spindle tuber disease.

Complete Answer:
- Viroid is the smallest virus that is responsible for causing disease in plants. It is found to be a free RNA and is devoid of protein coat that is typically present in viruses.
- The RNA of a viroid is of low molecular weight. They do not encode any protein to provide specific functions and thus their mechanism of systemic infection is based on sequestering the nucleic acid of the host cell and interacting with the genome of the host cell.
- It infects many hosts like peach, cherry, pear, apple, plum, nectarines, almonds and apricots.

The correct option is D i.e. their RNA is of high molecular weight.

Additional Information: Viroid was discovered by Theodor Otto Diener, a plant pathologist that is responsible for causing potato spindle tuber disease. The Pospiviroidae are a family of viroid having the first viroid to be discovered as PSTVd (potato spindle tuber viroid). PSTVd is called so because of the oblong tubers produced from infected plants.

Note: The replication mechanism involves RNA polymerase II that is an enzyme generally responsible for synthesis of messenger RNA from DNA but in viroid, it catalyzes rolling circle synthesis of new RNA using the viroid’s RNA as a template strand.
It is found that the human pathogen Hepatitis D virus is similar to that of viroid.