Viruses Flashcards
Basic virology
- have DNA or RNA NOT BOTH
- have no small ions or polysaccharides (they glycosylate proteins by using host enzymes
- either enveloped or naked (more difficult to destroy)
Viral shape (recognition of shape allows drugs to be designed to target them)
Filovirus - e.g. Ebola
Obligate intracellular parasites
- have no genes that encode for means of energy generation of protein synthesis
- hijack host organisms in order to support their own replication
Virus growth
Increase is sudden
- cell bursts releasing a huge number of viruses all at once
RNA or DNA
- single stranded SS or double stranded DS
- SS may be:
(+) can serve as mRNA and be directly translated into a protein - linear, circular or nicked
(-) cannot serve as mRNA so cannot be directly translated into a protein e.g. Ebola or HIV - unsegmented or segmented (allows reassortment of DNA - explains the adaptability of the flu virus)
Capsid
protein outer coat
- individual subunits are called capsomers
- protects the inner Nucleic acid from harsh environmental conditions
- may be involved in the attachment to host cells
Either ICOSAHEDRAL OR HELICAL
Bacteriophage
Viruses that infect bacteria
- involved in the transfer of antibiotic resistance
- assist in the ability of the bacteria to infect cells
Successful infection and replication
host cell must have the cellular machinery the virus needs for replication
- the cell must contain a receptor for the virus to bind to via a ligand in order to initiate an infection
- the ligand is on the capsid of naked viruses and on the envelope of the enveloped viruses
There can be many different receptor involved in the infection process - some viruses can’t affect humans as our cells don’t have the correct receptors
Successful Replication
- infection is productive
- host cell is permissive for the virus
Baltimore Scheme
based on the relationship between the viral genome. And the mRNA used for translation during the expression of the viral genome
Medical Virology
- use the Nucleic acid type and envelope as the main classification
- representative of how easily the virus is destroyed by disinfectants
ENVELOPED viruses are generally more susceptible to disinfectants than non-enveloped
DNA viruses
ENVELOPED - Hepatitis B - Herpesvirus NON-ENVELOPED - papillomavirus (warts and cervical cancer)
RNA viruses
ENVELOPED - rubella - HIV (AIDS) NON-ENVELOPED - picornavirus (polio, hepatitis A, colds)
Effects of virus on host cell
drugs that suppress viral replication have no effect on integrated DNA
Death of cell - often during release of virus
Cytopathic effects - caused by viral replication
- inclusion bodies (site of active virus synthesis) e.g. Negri bodies of rabies virus
- syncytia formation (giant, multinucleated cells formed by the fusion of plasma membranes)
- chromosomal damage
- inhibitor of host cell protein, RNA or DNA synthesis
Cancer
- retroviruses - turn on cellular oncogenes that cause cells to proliferate uncontrollably
- inactivate tumour-suppressor proteins that normal act to keep the cell from going through the cell cycle uncontrollably
Ebola
RNA SS (-) Haemorratic - disorders blood clotting and integrity of blood vessels
