Biology Status

Structure Viroids are composed of small, circular, single stranded RNA molecules which have some double-stranded regions. The closed single-stranded RNA circle has extensive intra-strand base pairing and interspersed unpaired loops.   They consist of a short stretch of highly complementary circular single-stranded RNA without a protein coat.  The molecular weight of Viroid ranged between 85,000 and 1,30,000 daltons.  Viroids are 240-380 nucleotides long and all of them have dump-bell-shaped structures.  The range in size is approximately 20 nm.  Viroids are catalytic RNAs (ribozymes) that cleave RNA to produce fragments containing a 5'-hydroxyl and a 2', 3'-cyclic phosphate. Structure of PSTV:   H.J. Cross (1979) sequenced the nucleotide sequence of the potato spindle tuber virus (PSTV). The structure of PSTVd is as follows It consists of 359 ribonucleotides and is characterized by numerous intermolecular base pairing. The single-stranded circular RN...

Characteristic features of Viroids: More than 40 viroid species and many variants have been characterized. The characteristics features of Viroids are as follows: 1) It is an infectious RNA particle. 2) Viroids are made up of small single-stranded circular RNA having 240-380 nucleotides. 3) Viroids do not contain a protein coat/capsid or an envelope. 4) It has no coding capacity because the RNA of a viroid does not have an initiation code (AUG) for protein synthesis. 5) Circular RNA molecules are capable of autonomous replication. 6) Since viroids are RNA particles, they can be inactivated by ribonuclease digestion but are resistant to proteinase K and trypsin digestion. 7) Viroid has a smaller size than viruses. Its size is approximately 20 nm. 8) Viroids require host cell DNA-dependent RNA polymerase enzyme to replicate. Use host-encoded polymerase for replication. 9) Viroids infect only higher plants (exception: hepatitis D virus in humans is similar to viroid). 10) It is mainly fo...

The word VIROID is composed of two words ‘VIR (means virus)’ and ‘OID (means like)’. Thus, Viroid means virus-like organism/particle. Viroids were first discovered and named by the plant pathologist Theodor O. Diener in 1971 to describe the causal agent of the potato spindle tuber disease. The first viroid identified was Potato Spindle Tuber Viroid (PsTVd). A viroid is an infectious RNA particle formed from a single-stranded circular RNA. It infects only plants (except Hepatitis D in humans). Viroid may cause disease by triggering RNA slicing. Some are found in the infected host cell nucleus, others found in the chloroplast. More than 40 viroid species and many variants have been characterized. Definition: Viroids are infectious, non-protein-coating, highly structured small circular naked RNA molecules able to replicate autonomously and induce diseases in higher plants. The term viroid was coined by T.O. Diener (1971) to describe the causal agent of the potato spindle tuber disease. In...