What are viruses?
Intracellular obligate anaerobes// Viruses are microscopic organisms that can infect hosts, like humans, plants or animals. They’re a small piece of genetic information (DNA or RNA) inside of a protective shell (capsid). Some viruses also have an envelope. Viruses can’t reproduce without a host.
What do viruses attach to?
A virus attaches to a specific receptor site within the host cell
Plant Viruses
Mostly ssRNA viruses
Cannot penetrate cell walls on their own
Require vectors to spread
Fungi Viruses
Usually dsRNA viruses
Lack extracellular phase
Spread through hyphal fusion, spores, or cell division
Animal Viruses
DNA, RNA, enveloped or nonenveloped
Enter host cells via endocytosis, fusion, or receptor-mediated attachment.
Often cause acute, persistent, latent, or chronic infections.
RNA viruses often replicate in the cytoplasm
How are viruses specific for their host cells?
Viruses are specific to their host cells because of a “lock and key” mechanism: viral surface proteins bind to specific receptor molecules on the host cell’s membrane. This precise interaction determines which species and even which cell types within an organism can be infected, as cells that lack the correct receptor cannot be infected by that virus.
Bacteria Viruses
Usually dsDNA
Replicate in cytoplasm
Infect through receptor binding and injection of DNA.
What is the structure of the viral capsid?
A protein shell made of repeating subunits called capsomeres that form highly symmetrical shapes (helical or icosahedral) around the genetic material.
What is the function of the viral capsid?
To protect the genetic material and facilitate delivery of the genome into the host cell.
Origin of Viral Envelope
It is a lipid membrane stolen from the host cell membrane (e.g., plasma membrane, nuclear membrane) during budding.
Structure of the Viral Envelope
A lipid bilayer with virus-encoded glycoproteins (spikes) embedded in it.
Function of the Viral Envelope
To help the virus attach to host cells, evade the immune system, and fuse with the host cell membrane to allow entry.
Characteristics by which viruses are classified
DNA or RNA
Enveloped or non-enveloped
What is the lytic replication cycle?
a rapid viral reproduction process where a virus hijacks a host cell to create numerous new viruses, ultimately causing the cell to burst and release the new viral particles.
Where does the lytic replication cycle usually occur?
Inside a host cell
How many stages of the lytic replication cycle are there?
5
Stages of the lytic replication cycle in order
- (Attachment) Absorption
- Penetration
- (Biosynthesis) Replication
- Maturation
- (Lysis) Release
(Attachment) Absorption Stage of Lytic Cycle
the attachment site on the bacterial phage adheres to the receptor site of the host
Penetration Stage of Lytic Cycle
Bacteria; phage that adheres to the bacterial cell wall by use of bacterial phage enzyme.
- A hole is drilled into the bacteria and injects its genome within it.
(Biosynthesis) Replication Stage of Lytic Cycle
The genome is replicated by use of the host’s machinery
Maturation Stage of Lytic Cycle
new virions are created
Release (Lysis) Stage of Lytic Cycle
The lysosome (bacterial phage enzyme) is used to break down peptidoglycan within the bacteria. The cell wall becomes weaker. Undergoes osmotic lysis, releasing the replicated genomes
What is the lysogenic replication cycle?
a type of viral replication where the viral DNA integrates into the host cell’s genome and is copied along with the host’s DNA, resulting in a latent infection without immediate destruction of the host cell.
How in it’s stages does the lysogenic cycle differ from the lytic cycle?
In the lysogenic cycle, viral DNA integrates into the host cell’s DNA and remains dormant (a prophage), replicating with the host without killing it. In the lytic cycle, viral DNA stays separate, forces the cell to make new viruses immediately, and then lyses (bursts) the cell.
