Viroids and Prions

Introduction

Attempts to find the causative agents of previously unknown diseases have resulted in the discovery of non-living disease agents that are not viruses. These include particles made completely of RNA or protein that are capable of self-propagation at the expense of a host—a critical resemblance to viruses which allows them to cause disease. Viroids, virusoids, and proteinaceous prions have all been discovered thus far.

Viroids and Prions

Prions are infectious particles which lack nucleic acids, while viroids are tiny plant pathogens that lack protein coding.

Prions

Prions are infectious particles that are smaller than viruses and do not contain nucleic acids. They are named prions since they are proteinaceous (neither DNA nor RNA). It was once thought impossible to imagine an infectious agent that didn’t require nucleic acids, but Nobel Prize-winning scientist Stanley Prusiner’s pioneering work has persuaded the majority of biologists which such agents do exist.

Prions have been demonstrated to transmit fatal neurological diseases like kuru in human being and bovine spongiform encephalopathy (BSE) in cattle (often referred as mad cow disease). The disease was communicated between individuals of the same species through the intake of meat, nerve tissue, or internal organs. Kuru, a human-only species native to Papua New Guinea, was passed on from generation to generation through ritualistic cannibalism. BSE was first discovered in the United Kingdom, and it spread across cattle due to the practice of feeding nerve tissue from calves to other cattle. Individuals with kuru and BSE exhibit symptoms of lack of motor control and odd behaviours, such as uncontrollable bursts of laughing followed by death with kuru. Kuru was ruled by persuading the populace to give up their ceremonial cannibalism.

A prion is a misfolded rogue form of a normal protein (PrPc) identified in a cell. This infectious rogue prion protein (PrPsc) can cause other endogenous normal proteins to misfold, resulting in plaque formation. It can be created by a genetic mutation or arise spontaneously. Human and animal forms of transmissible spongiform encephalopathy are now recognised to be caused by prions (TSE).

Viroids

Viroids are infectious pathogens that only damage plants, earning the name plant pathogen.  Viroids are smaller than viruses and have ribonucleic acid (RNA) strands that are not covered with protein. To generate new clones of themselves, these creatures utilise the cellular machinery present in plant cells. It mostly affects all types of higher plants.

Viruses have the ability to devastate commercially important agricultural food crops grown in fields and orchards. Following the discovery of PSTV, more viroids that cause plant illnesses were discovered. Tomato planta macho viroid (TPMVd) infects tomato plants, resulting in chlorophyll loss, distorted and brittle leaves, and smaller tomatoes, resulting in a yield reduction in this field crop.

Virus

A virus is a non-cellular, infectious organism made up of genetic elements and proteins. It may enter and proliferate among living bacteria, plants, and mammals. Viruses cannot replicate outside of the host cell because they lack the essential cellular machinery. As a result, it enters and binds to a specific host cell, injecting its genetic element. Furthermore, the virus replicates by using the host’s genetic material before ripping open and releasing new viruses.

Function of Virus

A virus’s primary role is to transport its genome into a host cell, where it can be translated and transcribed by the host cell. The newly produced viruses are discharged from the host cell by causing the cell to split apart, waiting for the cell to die, or budding off through the cell membrane during the release.

Compare Viroids Prions and Viruses

Conclusion

Viruses are disease-causing, infectious, acellular, antigenic, obligatory parasitic nucleoprotein microorganisms capable of infecting and multiplying within the live cells of certain species. Viroids are infectious entities composed of naked, single-stranded RNA that are 100 times smaller than viruses.  The prions are the tiniest, misfolded, infectious particles, proteinaceous, made composed of glycoproteins alone. Lichens are composite creatures made up of algae (phycobiont) and fungi (mycobiont) that coexist in a symbiotic relationship.