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What type of genetic material can a virus have?
A virus can self-replicate without infecting a host cell.
False
Name one mechanism by which a virus can enter a host cell.
Direct penetration, fusion, or receptor-mediated endocytosis
The protein spikes that aid in viral infection are known as __________.
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Match the following viral mechanisms with their descriptions:
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Which method of viral release typically does not kill the host cell?
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RNA viruses generally have lower mutation rates than DNA viruses.
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What is the final step of the viral replication cycle?
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What role does hemagglutinin (HA) play in the influenza virus?
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Antigenic shift occurs only through point mutations in viral genes.
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What is the function of neuraminidase in the influenza virus?
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Antigenic ________ results from point mutations, producing new strains of the flu virus.
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Match the following influenza-related terms with their definitions:
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Which viruses are associated with antigenic shift leading to pandemics?
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Bacteriophages can be cultivated on agar plates like bacteria.
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What is a common consequence of antigenic drift in the influenza virus?
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Study Notes
What is a Virus?
- A virus is an acellular infectious agent that cannot reproduce on its own.
- Viruses must infect a cell to replicate.
- Examples of viruses include influenza, HIV, and Ebola.
Viral Structure
- Viruses vary in structure but share common features.
- RNA or DNA genome: Contains the virus's genetic information.
- Capsid of proteins: A protective protein shell surrounding the genome.
- Envelope Lipid Bi-layer: A membrane that surrounds the capsid in some viruses (e.g. influenza).
- Surface receptors: Spikes of protein or glycoprotein that help the virus attach to and enter host cells.
Viral Replication Cycle
- The replicative cycle of a virus depends on its genome.
- For example, ssRNA viruses replicate differently to dsDNA viruses.
Viral Replication Cycle: Attachment
- Proteins on the viral envelope or capsid bind to specific receptors on the host cell's surface.
Viral Replication Cycle: Penetration
- Viruses enter host cells through different mechanisms.
- Direct penetration: Only the viral genome enters the host cell (typical of bacteriophages).
- Fusion: Viral envelope fuses with the host cell membrane, allowing the capsid containing the genome inside.
- Receptor-mediated endocytosis: The virus attaches to host cell receptors, triggering endocytosis of the entire virus.
Viral Replication Cycle: Uncoating
- The virus removes its capsid (uncoats), exposing the viral genome to the cytoplasm.
Viral Replication Cycle: Transport to Nucleus
- The viral genome enters the host cell's nucleus.
Viral Replication Cycle: Synthesis (Transcription & Translation)
- The viral genome is replicated (transcribed in the nucleus).
- Viral proteins are produced (translated in the cytoplasm).
Viral Replication Cycle: Assembly
- Newly synthesized viral components (genome and capsid) are assembled into new viruses.
Viral Replication Cycle: Release
- New viruses are released from the host cell through viral shedding.
Viral Shedding
- Viral shedding happens through three main mechanisms.
- Apoptosis: Host cell lyses (breaks apart) and releases mature viral particles (naked viruses), killing the host cell.
- Budding: New viruses bud through the nuclear or plasma membrane, acquiring a new envelope. This does not kill the host.
- Exocytosis: Viruses leave the host cell using vesicles, not killing the host cell.
Influenza Virus
- Influenza virus is an enveloped RNA virus.
- RNA viruses mutate more frequently than DNA viruses, which can lead to new strain development.
- Influenza viruses have two proteins that are vital for infection:
- Hemagglutinin (H) spike: Binds to sialic acid receptors on host cells, aiding in viral entry.
- Neuraminidase (N) spike: Helps the virus penetrate the respiratory mucus and aids in viral shedding (budding) by cleaving sialic acid from host glycoproteins as it exits.
Antigenic Variation
- Antigenic variation in influenza occurs in two ways.
- Antigenic drift: Point mutations in the genes for Hemagglutinin and Neuraminidase, leading to new strains of influenza that host antibodies may not recognize.
- Antigenic shift: Reassortment of viral genes from two different influenza viruses infecting the same host cell creates a new virus with a different antigenic profile.
Antigenic Drift
- Antigenic drift causes localized flu epidemics due to the emergence of new influenza strains that host antibodies do not recognize.
Antigenic Shift
- Antigenic shift can lead to pandemics.
- Reassortment of genes from two different influenza viruses can generate new viruses with novel antigens, against which existing antibodies are ineffective.
- For example, the H5N1 (bird flu) and H1N1 (swine flu) viruses can reassort to produce a new, potentially pandemic strain.
Bacteriophage
- Bacteriophages (phages): Viruses that infect only bacterial cells.
- Phages cannot be grown on agar plates like bacteria, they require host cells, such as bacteria.
- Bacteriophage Lambda: An important model system for studying DNA and genes, contributing greatly to our understanding of molecular biology and protein synthesis mechanisms.
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Description
This quiz explores the fundamental concepts of viruses, including their definitions, structures, and replication cycles. Learn about the differences in types of viruses and how they interact with host cells. Perfect for biology students seeking to deepen their understanding of viral biology.
