Viral Replication Cycle Quiz

Viruses need a host cell for replication.
Viruses are obligate intracellular parasites.
Viruses are host-specific.
Viruses have a two-phase lifecycle, either residing in a dormant state within the host genome (lysogenic cycle) or hijacking the host cellular machinery for their own replication (lytic cycle).

A virus introduces its genome into a host cell to initiate replication by hijacking the host's cellular machinery to make copies of the virus.
Once the infection is complete, the newly replicated and assembled virus particles are released through lysis of the host cell into the surrounding environment.
The lytic cycle has steps which include: attachment, entry, replication, self assembly, and release.

Attachment: The phage attaches to the host cell surface to administer the DNA within the cell.
Entry: The DNA is injected by the phage into the host cell by penetrating the membrane of the cell.
Transcription: The DNA of the host cell is destroyed and the metabolism of the cell is modified to begin the biosynthesis of the phage.
Self Assembly: The replication of the phage DNA takes place within the cell, producing novel phage proteins and DNA.
Release: The newly produced phages are discharged from the infected cell looking for novel host cells to infect. Release during the Lytic Life Cycle of a Lytic Bacteriophage. A bacteriophage-coded enzyme breaks down the peptidoglycan in the bacterial cell wall causing osmotic lysis.

A viral genome infects the bacterial or archaeal cell and reproduces along with it, rather than taking control of the host cell and producing new virions.
Lysogeny is characterized by the integration of the bacteriophage nucleic acid into the host bacterium genome or formation of a circular replicon in the bacterial cytoplasm.
In this condition, bacteria continue to live and reproduce.
The genetic material of the bacteriophage is called a prophage.
It has steps like attachment, penetration, integration, replication, induction, synthesis, assembly and release.

Adsorption: Virus attached to the host cell.
Penetration: Entry genetic material is injected into the host cell.
Integration: The phage DNA integrates into the host chromosome forming a prophage.
Replication: The prophage replicate, viral DNA is copied along with the host cell DNA, each new daughter cell is infected with the virus.
Induction: When the daughter cell is induced, the viral DNA is excised.
Synthesis: The phage DNA and protein are synthesized using the host cell machinery.
Assembly: The phage DNA and protein are assembled to form new viruses.
Release: The virions are released on lysis of the host cell.

Host cell requirement: Viruses require a host cell to provide energy and synthetic machinery.
Viral Replication Cycle in Host Cell: The viral replication cycle causes dramatic biochemical and structural changes in the host cell, leading to cell damage.
Symptoms of Viral Diseases: The symptoms of viral diseases result from the immune response to the virus, attempting to control and eliminate the virus from the body.
Viral Release: Many animal viruses, such as HIV, leave infected cells of the immune system through a process called budding.

Virus particles attach to specific receptors on the host cell surface.
Receptors may be proteins or carbohydrate residues on glycoproteins or glycolipids.
Expression of receptors on host cells determines viral tropism.
Attachment phase influences viral pathogenesis and infection course.
Initial attachment may be facilitated by cations.
Firm binding requires specific receptors on the plasma membrane.
Viral surface molecules attach to cellular receptors.

Removal of virion's protein coat.
Release of genetic material.
Location of uncoating occurs in the same area as viral transcription, either in the cytoplasm or nucleus.

Virus types: dsDNA, ssDNA, dsRNA, +sense RNA, -sense RNA, RNA & DNA that reverse transcribe.
Diagram of a virus lifecycle and Lytic/Lysogenic Lifecycle diagrams are included.
Translation and protein synthesis: viruses employ a diverse array of host-directed strategies for efficient expression of viral proteins.
Lacking essential machinery of protein synthesis, viruses take advantage of the host apparatus.
Some viruses have co-opted eukaryotic sequence or structural elements for translation initiation.
Assembly: Formation of an immature virus requires assembly of the capsid, envelopment, and packaging of the nucleic acid genome within a host cell.
Assembly depends on the type of virus.
Can occur in plasma membrane, cytosol, nucleus, Golgi apparatus, or other locations.
Some viruses only insert their genome after the capsid is completed.
In other viruses, the capsid wraps around the genome as it's being copied.
Maturation: Final changes in an immature virion for an infectious virus particle.
Structural changes include proteolytic cleavage, disulfide bond formation, envelope maturation, envelope protein incorporation, lipid bilayer formation, genome condensation, genome packaging, and nucleocapsid formation.
Release: The final stage when newly assembled viruses leave the host cell.
Release methods include lysis (cytolytic) and budding (cytopathic).