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Definition and Properties of a Virus (6)
- Viruses are filterable agents.
- Viruses are obligate intracellular parasites.
- Viruses cannot make energy or proteins independently of a host cell.
- Viral genomes may be RNA or DNA but not both.
- Viruses have a naked capsid or an envelope morphology.
- Viral components are assembled and do not replicate by "division."
Consequences of Viral Properties
- Viruses are not living.
- Viruses must be infectious to endure in nature.
- Viruses must be able to use host cell processes to produce their components (viral messenger RNA, protein, and identical copies of the genome).
- Viruses must encode any required processes not provided by the cell.
- Viral components must self-assemble.
Steps in viral replication
- 1. Recognition of the target cell
- 2. Attachment
- 3. Penetration
- 4. Uncoating
- 5. Macromolecular synthesis
- Early messenger RNA (mRNA) and nonstructural protein synthesis- genes for enzymes and nucleic acid-binding proteins
- Replication of genome
- Late mRNA and structural protein synthesis
- Post-translational modification of protein
- 6. Assembly of virus
- 7. Budding of enveloped viruses
- 8. Release of virus
What steps occur during the early phase of the viral replication cycle?
the virus must recognize an appropriate target cell, attach to the cell, penetrate the plasma membrane and be taken up by the cell, release (uncoat) its genome into the cytoplasm, and if necessary, deliver the genome to the nucleus.
What steps occur during the late phase of the viral replication cycle?
- begins with the start of genome replication and viral macromolecular synthesis and proceeds through viral assembly and release. Uncoating of
- the genome from the capsid or envelope during the early phase abolishes its infectivity and identifiable structure, thus initiating the eclipse period.
Describe the eclipse and latent periods
- The eclipse period, like a solar eclipse, ends with the appearance of new virions after virus assembly.
- The latent period, during which extracellular infectious virus is not detected, includes the eclipse period and ends with the release of new viruses.
This structure determines which cells can be infected by a virus
VAP (Viral Attachment Protein). Binds to the receptor of the cells. The receptors for the virus on the cell may be proteins or carbohydrates on glycoproteins or glycolipids