Untitled Quiz

Study Notes

Classifies viruses based on their genome and mRNA synthesis mechanism.
Genome categories include:
- Double-stranded (ds) or single-stranded (ss)
- RNA or DNA
- Linear, circular, or segmented forms.
Viral genome replication methods include direct entry for +ssRNA and dsDNA, requiring specific polymerases:
- RNA-dependent RNA polymerase (RdRp) for synthesizing RNA from an RNA template.
- Reverse transcriptase for converting RNA to DNA.

Class 1: dsDNA
- Incorporated into host cell and transcribed using host RNA polymerase II.
- Example: Herpesviruses.
Class 2: ssDNA
- Replication via DNA-dependent DNA polymerase (DdDp), converting ssDNA to dsDNA before mRNA production.
- Example: Parvovirus.
Class 3: dsRNA
- Requires RNA-dependent RNA polymerase for replication.
- Not infectious as it cannot be directly translated to mRNA.
- Example: Rotavirus.
Class 4: +ssRNA
- Functions as mRNA; replication needs RdRp.
- Example: Hepatitis C virus (HCV).
Class 5: -ssRNA
- Requires RdRp for converting -ssRNA into +ssRNA and then mRNA.
- Example: Influenza and Ebola viruses.
Class 6: ssRNA Retrovirus
- Contains two copies of RNA and requires reverse transcriptase for replication.
- Example: Human Immunodeficiency Virus (HIV).
Class 7: dsDNA Retrovirus
- Replicates using DdDp.
- Example: Hepatitis B virus.

Structure:
- Features +ssRNA with two identical copies.
- Icosahedral nucleocapsid with matrix; contains reverse transcriptase, integrase, and nucleocapsid proteins.
Genome:
- Envelope proteins gp120 and gp41, which facilitate cellular receptor binding.
Receptors:
- CD4 on T lymphocytes; capable of infecting monocytes and macrophages.
Replication Steps:
- gp120 binds to CD4 and triggers conformational change for gp41 binding to CCR5 and CXCR4.
- Entry via receptor-mediated endocytosis and membrane fusion.
- Replication occurs in the cytoplasm and nucleus through reverse transcription.

Converts ssRNA to dsDNA in three steps:
- RNA-dependent DNA polymerization forms an RNA-DNA hybrid.
- RNase H degrades the RNA strand, leaving single-stranded DNA (ssDNA).
- DNA-dependent DNA polymerase synthesizes a complementary DNA strand.

Involves circularization of linear DNA and integration into host DNA using integrase enzyme.
Viral polyprotein is processed into functional proteins for capsid assembly.

Structure:
- Consists of +ssRNA and is enveloped with an icosahedral shape.
- Envelope proteins E1 and E2 facilitate viral entry.
Receptors:
- CD81 cellular receptor is crucial for entry.
Replication Steps:
- Glycoproteins bind to CD81, leading to receptor-mediated endocytosis.
- Viral genome operates as mRNA, processes through RdRp to create new genomes.
- Assembles in the cytoplasm and is released via exocytosis.

Class 4 Baltimore classification.
Replication:
- Virus binds to cellular receptors and enters via fusion.
- Translates +ssRNA and utilizes RdRp to synthesize -RNA.
- Viral particles bud into the endoplasmic reticulum (ER) and are released through exocytosis.