Complex: Icosahedral head + helical tail (e.g., bacteriophages).
Viruses are extraordinarily small, ranging from 20 to 300 nanometers:
Bacteriophage lambda: ~50 nm.
Mimivirus: Up to 750 nm, one of the largest known viruses.
Types of VirusesNote
Viruses do not grow like living organisms.
Their size is fixed, but they must remain small enough to enter their host cells and replicate efficiently.
Genetic Material: DNA or RNA?
Unlike living organisms (DNA only), viruses use DNA or RNA in varying forms:
Single-stranded (ss) or double-stranded (ds)
Linear or circular
RNA viruses are further classified:
Positive-sense RNA: Acts directly as mRNA
Negative-sense RNA: Requires transcription into mRNA first
Example
Coronaviruses like SARS-CoV-2 have single-stranded positive-sense RNA genomes approximately 30,000 bases long.
In contrast, HIV contains twosingle-stranded RNA molecules, which are reverse-transcribed into DNA within the host cell.
Enveloped vs. Non-Enveloped Viruses
Non-enveloped (naked): Only a protein capsid; resistant to desiccation, detergents, heat, and pH changes (common in plants and bacteriophages).
Enveloped: Host-derived lipid bilayer with viral glycoproteins; fragile outside hosts, easily destroyed by soap, alcohol, and drying (mostly animal viruses).
Enveloped and non-enveloped viruses
Unlock the rest of this chapter with aFreeaccount
Nice try, unfortunately this paywall isn't as easy to bypass as you think. Want to help devleop the site? Join the team at https://revisiondojo.com/join-us. exercitation voluptate cillum ullamco excepteur sint officia do tempor Lorem irure minim Lorem elit id voluptate reprehenderit voluptate laboris in nostrud qui non Lorem nostrud laborum culpa sit occaecat reprehenderit
Definition
Paywall
(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.
anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
Note
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.
Excepteur sint occaecat cupidatat non proident
Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt. Neque porro quisquam est, qui dolorem ipsum quia dolor sit amet, consectetur, adipisci velit.
Tip
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.
Questions
Recap questions
1 of 5
Question 1
Recap question
A newly discovered virus contains single-stranded negative-sense RNA as its genome. Which component must the virion carry to initiate infection in the host cell?
End of article
Want a cheatsheet?
View a summary cheatsheet for A2.3 Viruses (HL)
Lesson
Recap your knowledge with an interactive lesson
9 minute activity
Note
Introduction to Viral Diversity
Viruses are incredibly diverse entities that challenge our understanding of life.
They exist at the boundary between living and non-living, possessing characteristics of both.
Unlike living organisms, viruses lack cellular structures and cannot carry out metabolic processes on their own.
They must infect host cells to replicate.
AnalogyThink of viruses as biological USB drives - they carry genetic information but need a host "computer" (cell) to function and replicate.
DefinitionVirusA microscopic infectious agent that can only replicate inside the living cells of an organism. Viruses consist of genetic material (DNA or RNA) enclosed in a protein coat.
