A2.3 Viruses (HL) Flashcards
co-evolution(virus first) hypothesis
viruses coevolved with their current cellular hosts
probably nt true though
What is a shared feature of all viruses?
All have DNA or RNA and capsids
This is a fundamental characteristic that defines all viruses.
What is a capsid?
The protein shell that surrounds the genetic material of a virus
Capsids are essential for protecting viral genetic material.
How do RNA viruses differ from retroviruses?
Retroviruses carry RNA and use DNA intermediates to replicate & reverse transcriptase
retrovirus prone to mutation
Examples of non-retroviruses include influenza and COVID viruses.
What is an enveloped virus?
A virus with an outer lipid layer
Examples include coronaviruses.
Virus features
- 20-500 nm (small)
- NO cytoplasm & plasma membrane
- need electron microscopy
- have capsids
- have fixed size
- few/no enzymes
Viruses are too small to be seen by light microscopy.
lytic pathway
defiintion
A viral cycle where new virus particles are released during lysis of the host cell caused by lysozyme
Lysis is caused by an enzyme coded for by the virus genetic material.
latency
Period during which viral genes coding for a repressor protein prevent nucleic acid translation and transcription
The host cell continues to function normally during this period.
What triggers the transition from the lysogenic cycle to the lytic cycle?
An external event
This can cause the viral DNA to become active.
progressive (escape) hypothesis
Viruses originated from genetic elements within cells, such as plasmids or transposons and gained ability to move between cells
=> became surrounded by outer boundary
This theory explains the presence of mobile genetic elements in cells.
regressive (reduction) hypothesis
Viruses were once small, free-living cells that became parasitic over time leaving behind just the virus
This hypothesis is supported by bacteria like Rickettsia and Chlamydia.
What contributes to the rapid evolution of RNA viruses?
- High mutation rates
- Genetic material exchange
- Short generation times
Consequence of rapid evolution for HIV treatment?
Emergence of new HIV strains that may evade the immune system or antiviral drugs
This is due to high mutation rates during replication.
What is reassortment in the context of influenza viruses?
Exchange of genetic material when an influenza virus infects a host cell already infected with a different strain
This leads to the emergence of new strains with different characteristics.
Viruses rely on the host cell for…
energy, nutrients, replication machinery, transport
ANtigenic drift
accumulation of small changes to viral genetic material over time => host cant recognie
ex: HIV
Antigenic Shift
A major change in short time period => two or more viruses affect same cell at once => combine gentic material
ex: Influenza
Replication based on genome sructure (viruses)
- you want -RNA as template for +RNA
- usually - strand is transcribed _> +mrna
- if -mrna no => synthesised
*
4 viral genome strcuture
- ss DNA = Parovirus
- ssRNA = HIV
- dsDNA = bacteriophage lambda/herpes
- dsRNA = Rotavirus
enveloping process
- virus takes envelope form host
- envelope protects capsid & hides from immune system
- can become damaged by heat
Lytic pathwqy steps
- virus attaches to cell mmebrane of host cell
- virus infects host cell = inject DNA
- Virus uses hosts proteins & enzymes to biosynthesis
- virzs assembles into mature virions
- host does lysis = release virions into hist orgnaisms to infect more cells
=> like parasite having babies
Lysogenic pathway
virus invades and integrates into host cell
lysogenic pathway steps
- attachent of virus to host
- virus RNA/DNA integrates with host DNA (forms phage)
- lysogenic cell reproduce and divide (lysogeny)
- environmental event triggers lytic pathway
Lytic vs lysogenic
lysogenic = new virus particles ARE NOT IMMEDIATELY released and do nit immdeiately cause disease => viral dna is inactive
