Virus and Subviral Agents Flashcards
Virus
A very small infective agent that consists of a core of nucleic acid and is dependent on a living host.
Viral structure
It consists of a DNA or RNA genome surrounded by a protein coat, called capsid. In some viruses the capsid is surrounded by an outer envelope.
Virus are classified based on…
Host range, types of hosts species, type of nucleic acid they contain and whether the nucleic acid is single or double-stranded.
Bacteriophages or phages
They are complex viruses that infect bacteria. They typically consists of a long molecule of dsDNA coiled within a polyhedral head.
Lytic cycle
The virus destroys the host cell.
Lysogenic cycle
The genome of a temperate virus (one that changes between lytic and lysogenic cycles) is replicated along with replication of the host’s DNA without causing death of the host cell.
Reverse transcriptase
It is used by retroviruses to transcribe their RNA genome into a DNA intermediate that becomes integrated into the host DNA.
The progressive or escape hypothesis
Virus escaped and moved from one cell and entered another through damaged cell membranes.
The regressive or reduction hypothesis
Viruses are remnants of cellular organisms; they evolved from free-living complex cellular ancestors. As they became parasitic, some of the genes necessary for protein synthesis were lost through evolution.
Virus-first hypothesis
Viruses predate or coevolved with their current cellular hosts. Viruses may have initially existed as self-replicating units. As they evolved, viruses produced enzymes for the synthesis of membranes and cell walls, leading to the formation of the first cells.
Satellites
They are smaller than viruses and only reproduce with the help of a helper virus.
Viroid
A smaller than a virus subviral agent. It consists of a short strand of RNA with no protein coat.
Prion
Consists only of protein.
