lecture 10 - viruses, helminths, and parasites Flashcards
Structure of viruses
There are two major structures of viruses
Viral Biodiversity
How does the HIV replication cycle begin?
HIV fuses with the host cell’s surface, allowing a capsid containing viral RNA and proteins to enter. The capsid disintegrates, and reverse transcriptase converts viral RNA into DNA.
What happens after HIV reverse transcriptase makes viral DNA?
The viral DNA enters the nucleus, where integrase inserts it into the host’s DNA.
How does the host cell contribute to HIV replication?
The host’s transcription machinery makes multiple copies of HIV RNA. Some copies become genomes for new viruses; others are used to make HIV proteins.
How are new HIV viruses formed and matured
New HIV RNA and proteins assemble at the cell surface to form immature viruses. After release, protease cleaves polyproteins to produce mature, infectious HIV.
Viral replication - 1
ATTACHMENT
The first step involves attachment of the virus particle to the cell surface. Depending on the virus, the viral proteins responsible for binding form either projections (glycoprotein spikes, fibres) or depressions in the virus surface.
Viral replication - 2
PENETRATION
Viruses can penetrate the host cell by either fusing with the host cell membrane as depicted on this slide or by priming the host signalling pathway leading to endocytosis
MECHANISMS OF VIRUS ENTRY INTO HOST CELL
Viral replication - 3
UNCOATING & SYNTHESIS - The shell of the capsid disintegrates and the HIV protein called reverse transcriptase transcribes the viral RNA into DNA. The viral DNA is transported across the nucleus, where the HIV protein integrase integrates the HIV DNA into the host’s DNA. The host’s normal transcription machinery transcribes HIV DNA into multiple copies of new HIV RNA.
Viral replication - 4
ASSEMBLY AND RELEASE OF VIRUSES
Some of the replicated RNA becomes the genome of new viruses, while the cell uses other copies of the RNA to make new HIV proteins. The new viral RNA and HIV proteins move to the surface of the cell, where a new, immature HIV forms. Finally, the virus is released from the cell, and the HIV protein called protease cleaves newly synthesized polyproteins to create a mature infectious virus.
What is classification?
The arrangement of organisms into taxonomic groups according to their observed similarities.
Classical Linnaean hierarchical system below
Past viral classification systems:
Haphazard (not a system at all) Here, vertebrate viruses have been named according to:
the type of disease caused (Japanese encephalitis virus),
the sites in the body affected or from which the virus was first isolated (rhinovirus, adenovirus)
the places from where they were first isolated (Ebola virus, Nipah virus)
the scientists who discovered them (Epstein-Barr virus), or
Due to common cultural perceptions e.g. influenza ‘influence’ of bad air or dengue ‘evil spirit’
Current Viral classification systems
International Committee on the Taxonomy of Viruses (ICTV) nomenclature.
Still based on classical Linnaean hierarchical system but primarily depends on the genome and nucleic acid material of the viruses
A complete catalog of known viruses is maintained by the ICTV at ICTVdb.
Current Viral classification systems - Baltimore classification system
The most commonly-used system for viruses
It was developed by Nobel Prize-winning biologist David Baltimore in the early 1970s.
The Baltimore classification system groups viruses according to how the mRNA is produced during the replicative cycle of the virus.
Baltimore Classification of Animal Viruses
Antigenic drift
virus in china
Helminth Parasites
Adaptations
