Untitled Quiz
50 Questions
3 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What does the Latin word "virus" mean?

Poison or venom

Viruses can reproduce independently of living cells.

False

What are the two main types of nucleic acid found in viruses?

  • DNA and RNA (correct)
  • DNA and Protein
  • RNA and Protein
  • DNA and Carbohydrates

    • What is the name for a complete virus particle?

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

    All viruses have the same basic structure.

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

    What are the two phases in which viruses can exist?

    <p>Extracellular and intracellular</p> Signup and view all the answers

    Name three ways in which viruses are different from living cells.

    <p>Their simple, acellular organization, the presence of either DNA or RNA (but not both), their inability to reproduce independently of cells.</p> Signup and view all the answers

    What is the name of the protein coat that surrounds a virus's genetic material?

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

    The capsid is composed of protein subunits called capsomeres.

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

    What is the name for the capsid that contains the genetic material?

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

    Match the following parts of a virus with their functions:

    <p>Capsid = Protects the viral genome Spike = Helps the virus attach to a host cell Envelope = Provides an additional layer of protection Nucleocapsid = The core of the virus containing the genetic material</p> Signup and view all the answers

    What are the two main categories of viruses based on their outer layers?

    <p>Enveloped and naked</p> Signup and view all the answers

    What is the origin of a virus's envelope?

    <p>The host cell's nuclear or plasma membrane</p> Signup and view all the answers

    All viruses have a protein coat.

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

    Which of the following factors are used to classify viruses?

    <p>All of the above</p> Signup and view all the answers

    What is the term for a group of similar viruses that share common characteristics?

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

    All viruses can infect any type of cell.

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

    What is the term for the specific cellular target of a virus within a host organism?

    <p>Tissue tropism</p> Signup and view all the answers

    The rabies virus has a narrow host range.

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

    What are the two main categories of viral genomes?

    <p>DNA and RNA</p> Signup and view all the answers

    All DNA viruses replicate in the host cell's cytoplasm.

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

    What are the two main types of RNA viruses based on their strand directionality?

    <p>+ve stranded and -ve stranded</p> Signup and view all the answers

    Retroviruses replicate their genomic RNA directly into new RNA copies.

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

    Match the following viral families with their primary type of nucleic acid.

    <p>Hepadnaviruses = DNA Picornaviruses = RNA Paramyxoviruses = RNA Herpesviruses = DNA Retroviruses = RNA</p> Signup and view all the answers

    What are the four main steps involved in viral replication?

    <p>Host cell invasion, hijacking the metabolism, producing genome copies, destroying the host cell.</p> Signup and view all the answers

    Bacteriophages can only replicate using the lytic cycle.

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

    Match the following steps in the lytic cycle of a bacteriophage with their descriptions.

    <p>Attachment = The phage binds to specific receptors on the bacterial cell surface. Penetration = The phage injects its DNA into the bacterium. Biosynthesis = The phage DNA uses the host cell's machinery to produce new viral components. Maturation = New viral components are assembled into complete phage particles. Release = New phage particles are released from the cell, potentially lysing the cell.</p> Signup and view all the answers

    What is the term for a phage DNA that has integrated into the bacterial chromosome?

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

    The lysogenic cycle always results in the immediate lysis of the host cell.

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

    What is the main difference between the lytic cycle and the lysogenic cycle of bacteriophages?

    <p>The lytic cycle results in the immediate lysis of the host cell, while the lysogenic cycle allows the viral DNA to integrate into the host genome and remain dormant for an extended period.</p> Signup and view all the answers

    Animal viruses always destroy the host cell during replication.

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

    What is the main function of spikes in animal viruses?

    <p>Attaching to the host cell</p> Signup and view all the answers

    All animal viruses enter the host cell through endocytosis.

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

    The uncoating process refers to the removal of the viral capsid from the genome.

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

    Match the following viral stages with their descriptions:

    <p>Attachment = The virus binds to specific receptors on the host cell. Penetration = The virus enters the host cell through endocytosis or membrane fusion. Biosynthesis = The viral genome uses the host cell's machinery to produce new viral components. Maturation = New viral components are assembled into complete viral particles. Release = New virions are released from the host cell through budding or lysis.</p> Signup and view all the answers

    What is the term for a viral infection that does not immediately result in the production of new virions?

    <p>Latent infection</p> Signup and view all the answers

    Herpes simplex virus-1 can only cause a productive infection.

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

    HIV infection always results in the immediate death of the host cell.

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

    What is the name for the integrated viral DNA within the host genome that remains dormant during latent infection?

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

    Viral gene therapy is completely risk-free.

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

    What are the two main types of subviral particles that are smaller than viruses and can cause disease?

    <p>Viroids and prions</p> Signup and view all the answers

    Viroids can infect both animals and plants.

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

    What is a prion?

    <p>An infectious protein that lacks nucleic acid.</p> Signup and view all the answers

    Mad cow disease is caused by a virus.

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

    What is the name for the infectious protein responsible for Mad Cow Disease?

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

    Prions can only be transmitted through direct contact.

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

    Which of the following is NOT a characteristic of prions?

    <p>They are highly susceptible to heat sterilization</p> Signup and view all the answers

    Prions can be destroyed by conventional sterilization methods.

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

    What is the term for the group of diseases caused by prions?

    <p>Transmissible spongiform encephalopathies (TSEs)</p> Signup and view all the answers

    Viroids and prions are thought to share a common evolutionary origin.

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

    Study Notes

    Introduction to Viruses

    • Viruses are simple, acellular entities.
    • They are obligate intracellular parasites.
    • They can only reproduce inside living cells.
    • Latin for 'poison' or 'venom'.
    • Possess either DNA or RNA, but not both.

    Viral Structure

    • A complete virus particle is a virion.
    • Composed of one or more molecules of DNA or RNA, enclosed in a protein coat.
    • Some viruses have additional complex layers like carbohydrates, lipids, and additional proteins.

    Viral Phases

    • Viruses can exist in two phases: extracellular and intracellular.
    • In the extracellular phase, they have few, if any, enzymes, and cannot reproduce independently of living cells.
    • In the intracellular phase, they replicate nucleic acids and induce host metabolism to synthesize virion components. Eventually, complete virus particles (virions) are released.

    Differences Between Viruses and Living Cells

    • Simple, acellular organization.
    • Presence of either DNA or RNA but not both.
    • Inability to reproduce independently from host cells and carry out cell division.

    Generalized Structure of Viruses

    • Naked virus: Simplest, consisting of a capsid surrounding a nucleic acid strand.
    • Enveloped virus: A nucleocapsid surrounded by a flexible membrane (envelope). The envelope often has viral proteins (spikes) inserted into it.

    History of Viral Discovery

    • Early attempts at preventing viral diseases predate the discovery of viruses themselves.
    • Lady Wortley Montagu observed Turkish women inoculating their children against smallpox.
    • Edward Jenner developed the first vaccine against smallpox using cowpox material.
    • Louis Pasteur used the term "virus" for any living infectious disease agent.
    • Charles Chamberland's porcelain bacterial filter allowed the isolation of viruses.
    • Dimitri Ivanowski studied tobacco mosaic disease, finding that extracts could cause the disease even after filtering out bacteria.
    • Martinus Beijerinck proposed the existence of a filterable virus.
    • Friedrich Loeffler and Paul Frosch identified a virus associated with hoof-and-mouth disease of cattle.
    • Walter Reed's work on yellow fever helped establish viruses as distinct disease-causing agents.
    • Frederick Twort and Felix d'Hérelle discovered bacteriophages.
    • Wendell Stanley crystallized the tobacco mosaic virus.
    • Development of electron microscopes allowed visualization of viruses.

    Viral Size

    • Virions range in diameter from about 10 to 400 nm.
    • The smallest viruses are slightly larger than ribosomes.
    • Poxviruses are relatively large and visible with light microscopes.
    • Most viruses require electron microscopes for visualization.

    Unique Viral Features

    • Lack organelles, cytoplasm, and nuclei.
    • Composed of core nucleic acid and a protein coat.
    • Genetic material of most viruses is either DNA or RNA; usually coiled or folded to conserve space.
    • Nucleic acid is linear or circular.

    Capsid

    • The protein coat of a virus is called the capsid.
    • Provides shape and symmetry to the virus.
    • Protective layer.
    • Composition of amino acids resist temperature, pH, and other environmental fluctuations.
    • Capsomeres are protein subunits forming the capsid.

    Nucleocapsid

    • The capsid enclosing the genetic material (DNA or RNA).
    • Protects viral genetic material.
    • Aids in its transfer between host cells.

    Spikes

    • Some viruses have capsid proteins transformed into spikes.
    • Help with virus attachment and penetration.

    Virion

    • A complete and infectious virus outside its host cell.

    Naked vs. Enveloped Viruses

    • Naked viruses consist only of a nucleocapsid.
    • Enveloped viruses have a membrane (envelope) surrounding the nucleocapsid.

    Composition of Envelopes

    • Composed of lipids and proteins acquired from the host cell during replication.
    • Unique to each virus type.
    • Loss of the envelope or alteration in capsid symmetry can affect infectivity.

    Animal Virus Envelopes

    • Often arise from host cell nuclear or plasma membranes.
    • Envelope proteins are encoded by viral genes.
    • Often project from the surface as spikes (peplomers).

    Viral Shapes

    • Viruses are grouped based on nucleocapsid symmetry.
      • Helical: Tightly wound coil (e.g., tobacco mosaic virus, rabies virus).
      • Icosahedral: 20 triangular faces (e.g., herpes simplex virus, poliovirus).
      • Complex: Combination of helical and icosahedral symmetry (e.g., bacteriophages, smallpox virus).

    Host Range of Viruses

    • Host refers to the organisms a virus can infect, determined by capsid structure.
    • Most viruses have a narrow host range (e.g., specific bacteriophages affecting only certain bacterial species).
    • Some viruses have a broad host range, affecting numerous warm-blooded animals (e.g., rabies virus).

    Tissue Tropism

    • Many viruses infect specific cell types or tissues within a multicellular host, even within their host range.
    • This is termed tissue tropism.
    • Host range and tissue tropism are linked to virus infectivity.

    Viral Nomenclature

    • Names are usually given based on the disease they cause, the location of isolation, or morphologic factors.

    Classification of Viruses

    • Based on chemical and morphological criteria, specifically nucleic acid (size, symmetry, enveloped or not).
      • DNA viruses
      • RNA viruses.

    DNA Viruses

    • May have single or double-stranded genomes; linear or segmented.
    • DNA polymerase replicates DNA to DNA copies.
    • Most viruses replicate in the host cell's nucleus. Poxviruses are an exception, replicating in the cytoplasm.

    RNA Viruses

    • Contain either single or double-stranded RNA; linear or segmented.
    • Enzymes replicate directly RNA-to-RNA, with some having complimentary + or - strand type.
    • Retroviruses replicate indirectly via a DNA intermediate (RNA to DNA to RNA).

    Viral Replication

    • Viruses invade host cells and hijack their metabolism to reproduce copies of the virus.
    • Bacteriophages use a lytic or lysogenic pathway.
    • Animals viruses have variation in method and outcome.
    • Lysis and budding are two possible release mechanisms for enveloped viruses, naked viruses are released as host cell lyses.
    • Viral replication includes steps: attachment, penetration, biosynthesis, maturation, and release.

    Bacteriophages

    • Viruses that infect bacteria are called bacteriophages.
    • The T-even phages are an example of bacteriophages.
    • Have the characteristic head and tail structures.
    • Tail fibers help identify bacterial species.
    • Virulent viruses cause bacterial lysis.

    Why Viruses Invade Other Cells

    • A virus's nucleic acid often encodes only a few genes needed for viral components and functions.
    • Dependence on the host's cellular machinery is high.

    Lysis Cycle

    • Steps in the bacteriophages' replication cycle: attachment, penetration, biosynthesis, maturation, and release.

    Attachment

    • Random collisions with bacterial cells.
    • Phage tail fibers attach to a complimentary receptor site on the bacterium's cell wall or appendages.

    Penetration

    • Lysozyme is released to break open cell wall portion.
    • Tail core penetrates cell wall once tail sheath contracts.
    • Viral DNA is injected into the host cell through the tail core.

    Biosynthesis

    • Phage DNA uses host bacterial machinery to produce multiple copies of viral genome and capsid.
    • mRNA translates and produces phage enzymes and proteins.

    Maturation

    • Viral components assemble into complete viral particles.
    • Assembly follows a step-by-step procedure.

    Release

    • Mature phage particles burst out of the ruptured bacterial cell.
    • Lysozyme degrades the bacteria cell wall in some phages.

    Lysogenic Cycle

    • Some temperate phages follow the lysogenic cycle.
    • Viral DNA (prophage) integrates into bacterial chromosome, thereby replicating with the host.
    • The prophage can remain dormant (latent) until conditions stimulate it to start a lytic cycle.

    Animal Virus Replication: Attachment

    • Animal viruses attach to host cells using spikes distributed on the capsid.

    Penetration (Animal Viruses)

    • Viral envelope may fuse with the host cell's plasma membrane and release nucleocapsid, or enter by endocytosis.
    • Nucleocapsid is uncoated.

    Biosynthesis and Maturation (Animal Viruses)

    • Viral nucleic acid provides instructions for synthesizing viral components.
    • Components may assemble in the nucleus or cytoplasm.

    Release (Animal Viruses)

    • Enveloped viruses can bud off from the plasma membrane or host cell, forming an envelope.
    • Naked viruses are released when the host cell ruptures.

    Latent Infection

    • Some DNA and retroviruses can cause latent infections, in which viral gene expression is suppressed, and viral components are not produced.
    • Examples (including herpes simplex virus) result in a provirus, an integrated viral genome.

    Virus-Like Agents

    • Viroids are small, infectious RNA molecules that cause plant diseases.
    • Prions are infectious proteins with no nucleic acid.
    • Examples of prion diseases include mad cow disease, scrapie, and Creutzfeldt–Jakob disease.

    Prion Formation, Propagation

    • Normal prion protein (PrPC) is converted to abnormal prion protein (PrPSc); the shape change is infectious.
    • Prion aggregation in tissues causes spongiform encephalopathies.

    Viral Cultivation

    • Inoculation into fertilized chicken eggs.
    • Cell cultures.

    Cell Cultures

    • Primary cultures (animal cells separated from a tissue).
    • Cells adhere to form a monolayer.
    • Cell lines (maintained cells that reproduce in a single layer).

    Viral Plaques

    • Visible areas of clearing on a cell monolayer.
    • Results from virus replication and host cell lysis.
    • Used in viral detection.

    Phage Typing

    • Methodology that uses bacteriophages to detect and identify specific bacterial strains.

    Viruses, Cancer

    • Viruses can cause or be involved in cancer development.
    • Viral genes that cause cancer are oncogenes.

    Oncogenic Viruses: Mechanism

    • Viruses can introduce oncogenes into host cells.
    • Some viral oncogenes can transform host proto-oncogenes into active forms; example V-Oncogenes from retroviruses.
    • Oncogenes can lead to uncontrolled cell proliferation; hence promoting tumor development.

    Proto-oncogenes

    • Normal cellular genes that can be converted into oncogenes via various mechanisms.
    • Play roles in cell growth, metabolism, and mitosis.

    Virotherapy

    • Use of viruses to treat diseases including cancer.
    • Some challenges include immune responses, controlling infectivity, ensuring safety, and target cells.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Virus Study (PDF)

    More Like This

    Untitled Quiz
    6 questions

    Untitled Quiz

    AdoredHealing avatar
    AdoredHealing
    Untitled Quiz
    18 questions

    Untitled Quiz

    RighteousIguana avatar
    RighteousIguana
    Untitled Quiz
    50 questions

    Untitled Quiz

    JoyousSulfur avatar
    JoyousSulfur
    Untitled Quiz
    48 questions

    Untitled Quiz

    StraightforwardStatueOfLiberty avatar
    StraightforwardStatueOfLiberty
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser