Viruses
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Questions and Answers

Viruses are complex cellular structures with intricate mechanisms for metabolism.

False (B)

What are the two main components of a virus?

  • Ribosomes and mitochondria
  • Nucleic acid and a protein coat (correct)
  • Cell membrane and cytoplasm
  • Nucleus and Golgi apparatus

    • Viruses are considered "______" because they require a host cell to replicate.

    obligate intracellular parasites

    Why are viruses considered to be at the edge of what we consider "life"?

    <p>Viruses exhibit some characteristics of living organisms, such as replication and evolution, but they lack the ability to carry out essential life functions independently. They are inactive outside of a host cell.</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Capsid = The protein coat surrounding the viral nucleic acid Nucleic acid = The genetic material of a virus, containing instructions for replication Lipid envelope = An outer membrane found in some viruses, derived from the host cell membrane RNA-dependent RNA polymerase = An enzyme carried by some RNA viruses to replicate their RNA</p> Signup and view all the answers

    Which of the following is NOT a characteristic of viruses?

    <p>They have a nucleus and cytoplasm. (B)</p> Signup and view all the answers

    RNA viruses are generally more stable than DNA viruses.

    <p>False (B)</p> Signup and view all the answers

    What is the protective protein shell that surrounds a virus's genetic material called?

    <p>Capsid</p> Signup and view all the answers

    The process by which some viruses exit a host cell without causing immediate destruction is called ______.

    <p>Budding</p> Signup and view all the answers

    Match the following viral infection types with their corresponding characteristics:

    <p>Lytic Infection = Results in the destruction of host cells. Latent Infection = Virus enters a dormant state within the host cell. Chronic Infection = Slow and continuous viral replication without immediately killing the host cell. Transforming Infection = Alters host cell DNA, potentially leading to uncontrolled cell growth.</p> Signup and view all the answers

    Which type of virus is known for its ability to reverse transcribe RNA into DNA?

    <p>Retrovirus (B)</p> Signup and view all the answers

    Viruses are typically larger than bacteria.

    <p>False (B)</p> Signup and view all the answers

    What is the name of the complete viral particle that exists outside a host cell?

    <p>Virion</p> Signup and view all the answers

    The process of viral DNA integrating into a host's genome is called ______ and can occur in ______ viruses.

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    Which of the following is a method used by viruses like HIV to exit host cells?

    <p>Budding (D)</p> Signup and view all the answers

    Fusion occurs when a virus enters a host cell by injecting its genetic material directly into the cytoplasm without merging with the host cell membrane.

    <p>False (B)</p> Signup and view all the answers

    What are the specific proteins on the viral envelope that bind to receptors on the host cell surface during the attachment stage of fusion?

    <p>Glycoproteins</p> Signup and view all the answers

    After binding to the host cell, viral fusion proteins undergo a ______ change to bring the viral and host membranes close together.

    <p>conformational</p> Signup and view all the answers

    Which type of fusion occurs within an endosome, triggered by a low pH environment?

    <p>Endosomal Fusion (B)</p> Signup and view all the answers

    Match the following viral examples with their corresponding fusion types:

    <p>HIV = Direct Fusion Influenza = Endosomal Fusion Herpesviruses = Direct Fusion Rabies = Endosomal Fusion</p> Signup and view all the answers

    Viruses can only cause diseases and have no potential benefits in research or medicine.

    <p>False (B)</p> Signup and view all the answers

    Give one example of how viruses have been used in groundbreaking scientific advancements.

    <p>Gene therapy</p> Signup and view all the answers

    Despite their ______ size and simplicity, viruses have a profound impact on biology, healthcare, and research.

    <p>small</p> Signup and view all the answers

    Which of the following is NOT a potential benefit of viruses?

    <p>Increasing antibody production in host cells (E)</p> Signup and view all the answers

    What type of viruses are known to have a higher mutation rate?

    <p>RNA viruses (C)</p> Signup and view all the answers

    Enveloped viruses are more fragile than non-enveloped viruses.

    <p>True (A)</p> Signup and view all the answers

    What process do enveloped viruses mainly use to enter host cells?

    <p>fusion</p> Signup and view all the answers

    The virus leaves the host cell in a process known as ________.

    <p>release</p> Signup and view all the answers

    Match the following types of viruses with their characteristics:

    <p>RNA viruses = Higher mutation rates DNA viruses = Stable genomes Enveloped viruses = More fragile Non-enveloped viruses = More robust</p> Signup and view all the answers

    Which of the following is a function of capsids in viruses?

    <p>Protect genetic material (A)</p> Signup and view all the answers

    The lysogenic cycle leads to immediate cell death.

    <p>False (B)</p> Signup and view all the answers

    Name a viral enzyme that allows retroviruses to convert RNA into DNA.

    <p>reverse transcriptase</p> Signup and view all the answers

    The first vaccination strategy used the _______ virus to protect against smallpox.

    <p>cowpox</p> Signup and view all the answers

    Which of the following examples is a DNA virus?

    <p>Smallpox (A)</p> Signup and view all the answers

    What is the primary composition of a virus?

    <p>Genetic material and a protein shell (D)</p> Signup and view all the answers

    RNA viruses typically mutate rapidly, making them easier targets for vaccines.

    <p>False (B)</p> Signup and view all the answers

    Name one virus associated with cancer.

    <p>Human papillomavirus (HPV)</p> Signup and view all the answers

    Viruses that have an inert state outside a host cell are referred to as ______.

    <p>virions</p> Signup and view all the answers

    Match each type of viral infection with its characteristic:

    <p>Lytic Infection = Destroys host cells Latent Infection = Enters dormant state Chronic Infection = Slow viral replication Transforming Infection = Alters host DNA for uncontrolled growth</p> Signup and view all the answers

    Which mechanism do some viruses use to exit a host cell without destroying it?

    <p>Budding (D)</p> Signup and view all the answers

    All viruses have a lipid envelope.

    <p>False (B)</p> Signup and view all the answers

    What is an example of a chronic viral infection?

    <p>Hepatitis B virus</p> Signup and view all the answers

    Viruses that utilize reverse transcriptase to integrate their RNA into the host genome are called ______.

    <p>retroviruses</p> Signup and view all the answers

    What is the average size range of most viruses?

    <p>20 nm to 300 nm (A)</p> Signup and view all the answers

    Flashcards

    Virus

    A small infectious particle that requires a host cell to replicate.

    Nucleic Acid

    The genetic material of a virus, either DNA or RNA.

    Capsid

    The protein coat surrounding the viral nucleic acid.

    Acellular Entities

    Organisms not composed of cells, like viruses.

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    Obligate Intracellular Parasite

    Viruses that need a host cell to replicate and function.

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    Metabolism

    The set of life-sustaining chemical reactions in living organisms.

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    RNA Virus

    Virus type that uses RNA as its genetic material.

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    DNA Virus

    Virus type that uses DNA as its genetic material.

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    Mutate

    To change or evolve over time, a characteristic of some viruses.

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    Single-Stranded (ss) vs Double-Stranded (ds)

    Types of nucleic acid structures in viruses.

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    Budding

    The process by which viruses exit host cells, often seen in retroviruses like HIV.

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    Fusion

    The method through which a virus enters a host cell by merging its membrane with the host's.

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    Attachment

    The initial step where viral proteins bind to receptors on the host cell's surface.

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    Conformational Change

    Structural changes in viral proteins after they bind to the host cell, preparing for fusion.

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    Membrane Merging

    The point where viral and host membranes combine to form a fusion pore.

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    Direct Fusion

    A type of fusion where viruses like HIV merge their membrane directly with the host.

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    Endosomal Fusion

    Fusion that occurs within an endosome, often triggered by low pH, seen in viruses like influenza.

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    Viral Genetic Material

    The RNA or DNA that the virus delivers into the host's cytoplasm during fusion.

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    Glycoproteins

    Viral proteins that facilitate the attachment to host cells through receptor binding.

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    Impact of Viruses

    Viruses play roles in diseases, gene therapy, and advancing scientific research.

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    Mutation Rate of RNA Viruses

    RNA viruses mutate rapidly as RNA replication lacks proofreading.

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    Envelope in Viruses

    Lipid layer in some viruses, derived from host cell membranes, helps with host cell recognition.

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    Virus Attachment

    The process where a virus binds to specific receptors on the host cell’s surface.

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    Lytic Cycle

    Viral life cycle phase where the virus rapidly replicates and destroys the host cell.

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    Lysogenic Cycle

    Phase where the virus integrates its DNA into the host genome and remains dormant.

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    Reverse Transcriptase

    Enzyme in retroviruses converting RNA into DNA, crucial for certain viral processes.

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    Use of Viruses in Gene Therapy

    Modified viruses are used to deliver therapeutic genes to treat genetic disorders.

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    Viral Promoters in Research

    Strong DNA sequences used in genetic engineering to enhance gene expression.

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    First Vaccination Strategy

    Edward Jenner's use of cowpox to protect against smallpox marked the start of immunology.

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    Viruses Structure

    Viruses lack cellular structures, consisting only of genetic material in a protein shell called a capsid.

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    RNA vs. DNA Viruses

    Viruses can have RNA or DNA genomes; RNA viruses mutate quickly, while DNA viruses are more stable.

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    Lytic Infections

    Lytic infections destroy host cells as new viral particles are produced, causing severe symptoms.

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    Latent Infections

    In latent infections, viruses remain dormant in host cells and can reactivate later.

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    Chronic Infections

    Chronic infections involve slow and continuous viral replication without immediate cell death.

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    Transforming Infections

    Transforming viruses alter host cell DNA, leading to uncontrolled growth such as cancer.

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    Retroviruses

    Retroviruses reverse transcribe their RNA into DNA, integrating into the host genome.

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    Virus Morphology

    Viruses are classified by their shapes, such as helical or icosahedral, aiding identification.

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    Extracellular State

    Viruses outside host cells are inert and lack metabolic activity, existing as virions.

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    Viral Budding

    Budding is a process where viruses exit host cells, acquiring part of the membrane as an envelope.

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    Study Notes

    Viruses: A Detailed Overview

    • Viruses are infectious particles requiring a host cell to replicate. They consist of nucleic acid (genetic material) and a protein coat (capsid). Some have an outer lipid envelope.

    Viral Structure and Composition

    • Nucleic Acid: Can be DNA or RNA (but not both), single-stranded (ss) or double-stranded (ds). Carries instructions for viral protein production and replication. RNA viruses often have high mutation rates due to error-prone replication.

    • Capsid: Protects the nucleic acid, made of capsomeres (subunits). Capsid proteins facilitate attachment to host cells.

    • Envelope (in some viruses): Derived from the host cell membrane, containing glycoproteins for host cell recognition/attachment. Enveloped viruses are more fragile than non-enveloped.

    Viral Replication

    • Attachment: Viral surface proteins bind to host cell receptors (e.g., HIV to CD4, SARS-CoV-2 to ACE2).

    • Penetration: Viruses enter cells via fusion (enveloped) or endocytosis (non-enveloped).

    • Replication: Viruses hijack host machinery to replicate their genetic material (DNA viruses often in the nucleus, RNA viruses often in the cytoplasm). Retroviruses reverse transcribe RNA to DNA.

    • Assembly: New viral particles assemble from replicated genetic material and viral proteins.

    • Release: Viruses exit the host cell, often by killing it through lysis (non-enveloped) or budding (enveloped).

    Viral Life Cycles

    • Lytic Cycle: Immediate replication, causing host cell lysis (e.g., T4 bacteriophage). Leads to rapid disease symptoms.

    • Lysogenic Cycle: Virus DNA integrates into host DNA, dormant for a period (e.g., HIV). Can re-emerge.

    Viral Classification and Characteristics

    • RNA vs. DNA Viruses: RNA viruses (e.g., influenza, SARS-CoV-2) have higher mutation rates and require newer vaccines. DNA viruses (e.g., herpes) are more stable.

    • Non-Cellular Nature: Viruses lack cellular structures (nucleus, cytoplasm) and rely entirely on the host cell for energy and replication, making them a complex line between living and nonliving.

    • Structure Variation: Viruses vary significantly in structure; some are simple protein shells, and others have lipid envelopes. This impacts their infection and immune system evasion strategies.

    • Diverse Hosts: Viruses infect many organisms, from bacteria to humans.

    Viral Benefits and Applications

    • Strong Promoters: Viral promoters, like CMV, are highly efficient for gene expression in research and medicine.

    • Reverse Transcriptase Retroviruses' enzyme enables converting RNA to DNA, with wide use in molecular biology.

    • Gene Therapy Vehicles: Viruses can deliver therapeutic genes to treat genetic disorders by modifying them and removing harmful components.

    • Vaccine Development: Historically, viruses have been crucial in forming vaccination strategies (e.g., Jenner's smallpox vaccine using cowpox) and are still useful today for creating many vaccines.

    Viral Infections and Effects

    • Lytic: Destruction of host cells (e.g., influenza).

    • Latent: Dormancy in host cells, reactivation potential (e.g., cold sores).

    • Chronic: Continuous replication without immediate cell killing (e.g., hepatitis B).

    • Transforming: Alter host DNA; potentially causing cancer (e.g., some HPV types).

    • Retroviruses: Reverse transcribing RNA to DNA and integrating into the host genome (e.g., HIV); evades the immune system.

    Virus Sizes and Structures

    • Viruses are incredibly small, requiring electron microscopy for observation (range from 20nm-300nm in diameter). This is in contrast to cell sizes, which are often in micrometers. Unit conversions must be understood for virus sizes to enable comparison with bacteria and cells.

    Extracellular vs. Intracellular State

    • Extracellular: Inactive, in inert virion form (outside host).

    • Intracellular: Active, replicating via hijacking of host mechanisms (inside host).

    Budding and Fusion

    • Budding: A release mechanism for enveloped viruses (e.g., HIV, influenza), where the virion gains its envelope from the host's membrane, with less immediate cell lysis.

    • Fusion: Membrane merging between the virus and host cell, allowing the virus's genetic material to enter (e.g., HIV, other enveloped viruses). Different viruses may use fusion through different pathways.

    Virus Classification

    • Morphology: Helical, icosahedral, complex shapes.

    • Host Type: Infecting specific organisms, such as plants, animals, or bacteria (bacteriophages).

    • Genetic Material: DNA vs. RNA, single-stranded vs. double-stranded.

    • Pathology: Disease mechanisms, transmission, and severity.

    Viruses and Cancer

    • Certain viruses can trigger cancer by altering host DNA (e.g., HPV and cervical cancer).

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    Description

    This quiz explores the detailed structure and composition of viruses, including their nucleic acids and protein coats. Learn about the mechanisms of viral replication and the role of envelopes in various viruses. Test your understanding of how viruses attach to and penetrate host cells.

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