Biological Agents as Causes of Disease: Viruses Flashcards
What do viruses consist of?
Simple genome encapsulated in a protein coat called a capsid
Types of viruses
Lytic viruses
Lysogenic viruses
What are lytic viruses?
- DNA replicated and transcribed
- codes protein which creates more virus
- shut down processes not related to it
What are lysogenic viruses?
- Integrates DNA into host genome
- hidden
- period of inactivity
How are viruses classed?
They are classed by their genome type and hoer their mRNA (+ strand) is synthesised
Type I
DNA virus
DNA is transcribed into mRNA
most similar to normal cells
adenoviruses, herpes viruses etc.
Type II
DNA virus
ssDNA/ssRNA –> dsDNA –> mRNA
Type III
RNA virus
dsRNA –> mRNA Uses RNA transcriptase
segmented genomes
rotavirus
Type IV
RNA virus
RNA (+ strand) –> RNA ( - strand) uses RNA transcriptase
mRNA makes polyproteins that are cleaved
polio viruses, SARS viruses
Type V
RNA virus
ssRNA (-ve) –> mRNA
The vision carries RNA trascriptase
ebola viruses, influenza viruses
Type VI
Reverse transcribing virus
RNA –> ssDNA –> dsDNA –> mRNA. Uses reverse transcriptase. RNA primes and DNA polymerase. Then RNA polymerase
Retroviruses-enveloped-reverse transcriptase
HIV, human T cell lymphotrophic viruses, leukaemia
Type VII
Reverse transcribing virus
dsDNA then uses reverse transcriptase
DNA is made into genomic RNA
Hepatitis B virus
Entry methods
Rely on receptors present on host’s surface
- checkpoints at each step to ensure next phase not entered prematurely
What is papillomavirus?
Virus that infects epithelial cells, often leads to genital warts (benign)
What is transformation in terms of viruses?
Accidental integration of viral DNA into host genome –> unbalanced production of viral replication proteins –> malignant tumour
