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Questions and Answers
What role do scaffolding proteins play during the assembly of certain viruses?
What role do scaffolding proteins play during the assembly of certain viruses?
- They temporarily assist in the construction of the procapsid before being removed. (correct)
- They are crucial for self-assembly in a test tube.
- They form the final structure of the virion.
- They help in the budding process of enveloped viruses.
Which mechanism is commonly used by enveloped viruses to acquire their viral envelopes?
Which mechanism is commonly used by enveloped viruses to acquire their viral envelopes?
- Synthesis of new membranes exclusively.
- Direct lysis of host cells to expose the envelope.
- Modification of host cell membranes through direct synthesis.
- Budding through host cell membranes by incorporation of virus proteins. (correct)
What distinguishes the egress mechanism of bacteriophages from that of animal viruses?
What distinguishes the egress mechanism of bacteriophages from that of animal viruses?
- Bacteriophages initiate cell lysis, while animal viruses release virions over time. (correct)
- Both types of viruses require vesicle transportation to exit the cell.
- Bacteriophages bud from the plasma membrane, while animal viruses lyse their host cells.
- Animal viruses typically lyse their host cells, while bacteriophages are released slowly.
Which of the following statements best describes self-assembly in viruses?
Which of the following statements best describes self-assembly in viruses?
What is a key feature of the viruses that rely on directed assembly for virion construction?
What is a key feature of the viruses that rely on directed assembly for virion construction?
What is the role of packaging signals in viral genome selection during assembly?
What is the role of packaging signals in viral genome selection during assembly?
Which statement best describes the function of procapsid in virion assembly?
Which statement best describes the function of procapsid in virion assembly?
What mechanism do certain viruses use for egress from infected cells?
What mechanism do certain viruses use for egress from infected cells?
Which characteristic of viral membrane formation distinguishes enveloped viruses from non-enveloped viruses?
Which characteristic of viral membrane formation distinguishes enveloped viruses from non-enveloped viruses?
What is a key factor that enables some viruses to self-assemble from purified components?
What is a key factor that enables some viruses to self-assemble from purified components?
Flashcards
Self-assembly of viruses
Self-assembly of viruses
Some viruses, like tobacco mosaic virus, assemble their components spontaneously in a test tube, suggesting a similar process occurs inside infected cells.
Directed assembly of viruses
Directed assembly of viruses
More complex viruses, like herpesviruses, require complex intracellular processes to assemble their components.
Enveloped virus membrane acquisition
Enveloped virus membrane acquisition
Enveloped viruses obtain their membranes by either altering a host cell membrane for budding, or by directing the creation of a new membrane.
Bacteriophage virion release
Bacteriophage virion release
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Animal virus virion release
Animal virus virion release
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Concatemer definition
Concatemer definition
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Virion assembly - endonuclease
Virion assembly - endonuclease
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Viral genome packaging signal
Viral genome packaging signal
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Procapsid function
Procapsid function
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Viral genome selection
Viral genome selection
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Study Notes
General Introduction
- Viruses infect all life forms (eukaryotes, prokaryotes, plants, fungi)
- Viruses cause diseases, from common colds to lethal diseases like rabies, and contribute to cancer development.
- Viruses impact societal well-being
- Viruses have diverse genomes (RNA or DNA, single-stranded or double-stranded)
- Viruses are very small (less than 200 nanometers in diameter)
- Viruses can only replicate inside a host cell
- Viruses don't contain ribosomes (needed for protein synthesis)
- New virions are created through replication inside the host cell
- Viruses rely on host cells for building blocks (amino acids, nucleosides) and energy (ATP)
- Viruses modify host cells to enhance replication efficiency
Discovery of Viruses
- Beijerinck and Ivanovski independently discovered evidence of very small infectious agents
- Extracts from diseased plants with tobacco mosaic virus passed through filters
- Agents remained infectious after transfers, eliminating toxins as the cause.
- Beijerinck named them "viruses"
Viruses Living or Non-living?
- Ongoing debate over whether viruses are living or non-living
- Viruses have genes and replicate when infecting cells, suggesting a living quality
- Outside host cells, viruses exist as inert particles (virions), resembling non-living entities
- Strict definitions of life classify viruses as non-living
Origin of Viruses
- Four theories, not mutually exclusive:
- Regressive: remnants of cellular organisms
- Progressive: escaped nucleic acids from cells
- Symbiontic: intracellular microorganisms
- Virus-first: independent origin from self-replicating molecules.
Classification and Nomenclature
- International Committee on Taxonomy of Viruses (ICTV) established rules
- Nomenclature based on genome type (DNA or RNA, single- or double-stranded) and replication methods.
- Baltimore classification groups viruses by genome type
- dsDNA
- ssDNA
- dsRNA
- (+)ssRNA
- (-)ssRNA
- ssRNA with DNA intermediate
- dsDNA-RT
Structure of Viruses
- Virus particles (virions) outside host cells
- Virion structure: genome enclosed in capsid, sometimes with an outer envelope
- Capsids: protein structure, helical or icosahedral symmetry
- Envelopes: lipid membrane containing glycoproteins
- Various genome composition (dsDNA, ssRNA, dsRNA)
Viral Infection
- Viral aim is to replicate within a host cell
- Seven steps in viral replication cycle
- Attachment to cell
- Entry into cell
- Transcription to mRNA
- Translation to proteins
- Genome replication
- Assembly of virions
- Exit from cell
- Different mechanisms for attachment and entry (naked vs enveloped viruses)
- Crucial steps in viral replication: endocytosis, and fusion with host cell membranes
- Viral genomes can be replicated through various mechanisms to DNA/RNA/RNA-based.
Transport of Newly Synthesized Viral Proteins
- Viral proteins transported to various locations within infected cells (nucleus, etc.)
- Signal sequences direct proteins to their destinations
Virus Genome Replication
- DNA viruses replicate directly to DNA
- RNA viruses replicate through RNA or DNA intermediate
- Classification systems based on (+) and (-) strands
- Replication strategies (theta, sigma) and mechanisms
Assembly and Release (Virion Exit)
- Assembly process (and procapsids)
- How the virus leaves the infected host cell, envelope acquisition, and egress mechanisms
- Importance of proteins in viral assembly and release
Outcomes of Infection and Immune Responses
- Productive infection: new virions exit the host cell.
- Latent infection: virus genome persists.
- Abortive infection: no virus replication.
- Defective viruses: require helper virus for replication
- Host defenses have developed countermeasures to viruses
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Description
Explore the fascinating world of viruses, their structure, and their role in disease across diverse life forms. Learn about the pioneering discoveries of Beijerinck and Ivanovski that led to the understanding of these microscopic agents. This quiz will provide insights into how viruses replicate and interact with host cells.
