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Viruses possess the capability for independent reproduction outside of living host cells.
Answer: False
Viruses are obligate intracellular parasites and require the metabolic machinery of living host cells for replication; they cannot reproduce independently.
Viruses are restricted to infecting only animals and plants, excluding microorganisms.
Answer: False
Viruses infect all known forms of life, including microorganisms such as bacteria and archaea, in addition to animals and plants.
When external to a host cell, a virion comprises genetic material (DNA or RNA) enclosed by a protein coat termed a capsid, and occasionally a lipid envelope.
Answer: True
The virion, the complete infectious viral particle outside a host cell, consists of genetic material (DNA or RNA) encased in a protein capsid, and sometimes an outer lipid envelope.
The typical size of most viruses exceeds that of most bacteria.
Answer: False
Most viruses are significantly smaller than bacteria; virions are frequently approximately one-hundredth the size of most bacterial cells.
Viral genomes consist exclusively of double-stranded DNA.
Answer: False
Viral genomes can be composed of DNA or RNA, which can be single- or double-stranded.
DNA viruses typically replicate their genomes within the host cell's cytoplasm.
Answer: False
DNA viruses generally replicate in the host cell nucleus, whereas RNA viruses typically replicate in the cytoplasm.
All viruses are characterized by an outer lipid envelope derived from the host cell membrane.
Answer: False
While some viruses possess a lipid envelope derived from the host cell membrane, not all viruses have this structure; many are non-enveloped.
Based on the provided definition, what is the fundamental characteristic of a virus's replication process?
Answer: They require the living cells of an organism to multiply.
Viruses are obligate intracellular parasites, meaning they must infect a living host cell and utilize its machinery to replicate.
Which of the following life forms are NOT infected by viruses, according to the source?
Answer: Viruses infect all known forms of life, including plants, archaea, and bacteria.
The provided information indicates that viruses infect all known forms of life, encompassing plants, animals, fungi, bacteria, and archaea.
What term describes the complete viral particle when it is outside of a host cell?
Answer: Virion
The complete, infectious viral particle outside of a host cell is termed a virion.
How does the typical size of most viruses compare to that of a bacterium?
Answer: Most viruses are significantly smaller than most bacteria.
Viruses are typically much smaller than bacteria, often by a factor of 100 or more.
Which type of nucleic acid is NOT found in viral genomes according to the source?
Answer: Triple-stranded DNA
Viral genomes can be DNA or RNA, single or double-stranded, but triple-stranded DNA is not a recognized viral genome type.
How do DNA viruses typically differ from RNA viruses in their replication strategy?
Answer: DNA viruses replicate in the nucleus; RNA viruses usually replicate in the cytoplasm.
DNA viruses typically replicate in the host cell nucleus, while RNA viruses generally replicate in the cytoplasm.
Dmitri Ivanovsky is credited with the initial description of viruses in 1892, based on experiments involving the filtration of infectious tobacco plant sap.
Answer: True
Dmitri Ivanovsky's 1892 work demonstrated that the infectious agent from diseased tobacco plants could pass through filters designed to retain bacteria, marking an early step in identifying viruses.
Virology constitutes the scientific discipline dedicated to the study of viruses.
Answer: True
Virology is the branch of science specifically focused on the study of viruses.
The Latin word 'virus' originally signified 'vaccine'.
Answer: False
The Latin word 'virus' originally meant 'poison' or 'noxious liquid', reflecting early perceptions of disease-causing agents.
Bacteriophages were discovered independently by Frederick Twort and Félix d'Hérelle, a development that significantly advanced the field of virology.
Answer: True
The independent discoveries of bacteriophages by Twort and d'Hérelle were pivotal moments that spurred the growth and understanding of virology.
The term 'virus' originates from the Greek word signifying 'microbe'.
Answer: False
The term 'virus' is derived from the Latin word 'virus,' meaning 'poison'.
When was the existence of viruses first described, and by whom?
Answer: Dmitri Ivanovsky, 1892
Dmitri Ivanovsky first described the existence of viruses in 1892 through his work with tobacco mosaic disease.
What is the name of the scientific discipline focused on the study of viruses?
Answer: Virology
The scientific study of viruses is known as virology.
The word 'virus' is derived from a Latin term that originally meant:
Answer: Poison
The Latin word 'virus' originally meant 'poison' or 'noxious liquid'.
Viruses are typically classified into five principal morphological types: helical, icosahedral, prolate, enveloped, and complex.
Answer: True
Morphological classification of viruses commonly includes helical, icosahedral, prolate, enveloped, and complex structures.
Giant viruses, such as Mimivirus, are characterized by their small size and simple genomes.
Answer: False
Giant viruses, exemplified by Mimivirus, are distinguished by their exceptionally large size and substantial genomes, contrary to being small and simple.
The Baltimore classification system groups viruses according to their size and shape.
Answer: False
The Baltimore classification system categorizes viruses based on their genome type and their method of mRNA production, not size and shape.
Bacteriophages are viruses that infect bacteria and exhibit maximal abundance in terrestrial soil environments.
Answer: False
Bacteriophages are most abundant in aquatic environments, not terrestrial soil.
Bacteria are devoid of defense mechanisms against bacteriophages.
Answer: False
Bacteria possess sophisticated defense mechanisms against bacteriophages, including restriction-modification systems and CRISPR-Cas systems.
The International Committee on Taxonomy of Viruses (ICTV) is responsible for classifying viruses according to their symptoms.
Answer: False
The ICTV classifies viruses based on shared properties and genetic relationships, not primarily on symptoms.
Giant viruses, such as Mimivirus, are exclusively observable through advanced electron microscopy.
Answer: False
While many viruses require electron microscopy, some giant viruses, like Mimivirus, are large enough to be visible under a basic optical microscope.
Bacteriophages are principally recognized for their infection of plant cells.
Answer: False
Bacteriophages are viruses that specifically infect bacteria, not plant cells.
The Baltimore classification system categorizes viruses into seven distinct groups predicated on their genome and mRNA production strategy.
Answer: True
The Baltimore classification system is based on the nature of the viral genome and its replication pathway concerning mRNA synthesis, resulting in seven distinct groups.
Which of the following are NOT among the five main morphological types of viruses mentioned?
Answer: Bacterial
The five main morphological types are helical, icosahedral, prolate, enveloped, and complex. 'Bacterial' is not a morphological type of virus.
What distinguishes 'giant viruses' from most other viruses?
Answer: Their exceptionally large size and substantial genomes.
Giant viruses are characterized by their unusually large physical dimensions and extensive genomes compared to typical viruses.
The Baltimore classification system groups viruses based on:
Answer: Their genome composition and mRNA production method.
The Baltimore classification system categorizes viruses into seven groups based on their genome type (DNA/RNA, single/double-stranded) and how they generate mRNA.
Where are bacteriophages found to be most abundant?
Answer: In aquatic environments
Bacteriophages are exceptionally abundant, particularly in aquatic environments, where they are considered the most numerous biological entities.
Which of the following is a defense mechanism bacteria use against bacteriophages?
Answer: Utilizing CRISPR-Cas systems.
CRISPR-Cas systems provide bacteria with adaptive immunity against phages by targeting and degrading previously encountered viral genetic material.
What is the primary role of the International Committee on Taxonomy of Viruses (ICTV)?
Answer: To establish and maintain a unified system for classifying viruses.
The ICTV is responsible for developing and maintaining a standardized, hierarchical system for the classification and naming of viruses.
Which of the following viral groups in the Baltimore classification system uses a single-stranded RNA genome with a positive sense (+ssRNA)?
Answer: Group IV ((+)ssRNA)
Group IV viruses in the Baltimore classification system possess a positive-sense single-stranded RNA genome.
The regressive hypothesis posits that viruses evolved from complex molecules that underwent co-evolution with cellular entities.
Answer: False
The regressive hypothesis suggests viruses evolved from more complex, free-living organisms that subsequently lost genetic material. The hypothesis involving co-evolution with cells from complex molecules is termed the co-evolution hypothesis.
The determination of viral evolutionary origins is straightforward owing to the abundance of fossilized viral evidence.
Answer: False
The evolutionary origin of viruses is challenging to determine definitively because viruses do not fossilize; scientists rely on molecular techniques and indirect evidence.
The 'virocell' model proposes that individual virions represent the living form of a virus.
Answer: False
The virocell model suggests that the infected host cell itself can be considered the 'living form' of the virus, with virions analogous to spores.
Viruses predominantly impede evolution through the reduction of genetic diversity.
Answer: False
Viruses contribute to evolution by facilitating horizontal gene transfer, thereby increasing genetic diversity and driving evolutionary change.
Which hypothesis suggests viruses originated from genetic elements like plasmids that escaped from cells?
Answer: The cellular origin hypothesis
The cellular origin hypothesis posits that viruses arose from mobile genetic elements that escaped from cellular genomes.
Why is studying the evolutionary origin of viruses particularly challenging?
Answer: Viruses do not leave fossil records.
The absence of fossilized viral evidence makes reconstructing their evolutionary history particularly difficult.
How do viruses contribute significantly to evolution?
Answer: By acting as agents of horizontal gene transfer between species.
Viruses facilitate horizontal gene transfer, introducing genetic variation that drives evolutionary adaptation and change across species.
Influenza and rabies exemplify common human diseases caused by viruses.
Answer: True
Influenza and rabies are indeed well-known examples of human diseases caused by viral pathogens.
Viral latency denotes a state wherein a virus actively causes severe symptoms immediately upon infection.
Answer: False
Viral latency is characterized by a period of inactivity or dormancy within the host cell, often without causing immediate symptoms.
Airborne transmission, facilitated by coughing and sneezing, is a common route for viral spread between hosts.
Answer: True
Respiratory droplets expelled during coughing and sneezing are a primary mechanism for the airborne transmission of many viruses.
An epidemic is a viral outbreak that has spread globally, whereas a pandemic is confined to a specific region.
Answer: False
A pandemic is defined as a global outbreak, while an epidemic is typically confined to a specific region or population.
Certain viruses contribute to cancer development through the disruption of cell cycle regulation.
Answer: True
Oncogenic viruses can induce cancer by interfering with cellular mechanisms that control cell growth and division, such as cell cycle regulation.
HIV evades the immune system primarily through extremely slow replication.
Answer: False
HIV evades the immune system through multiple strategies, including rapid mutation of surface proteins, rather than solely through slow replication.
Human papillomavirus (HPV) and Hepatitis B virus (HBV) are examples of viruses associated with cancer development.
Answer: True
Certain strains of HPV and HBV are recognized oncogenic viruses linked to the development of various cancers.
Antigenic shift involves minor, gradual alterations in influenza virus surface proteins resulting from point mutations.
Answer: False
Antigenic shift refers to major changes due to genetic reassortment, while minor gradual changes from point mutations are termed antigenic drift.
Herpesviruses establish latency through the active destruction of host cells immediately upon infection.
Answer: False
Herpesviruses establish latency by remaining dormant and inactive within host cells, not by actively destroying them upon initial infection.
Cytopathic effects are advantageous changes induced by viruses that augment host cell function.
Answer: False
Cytopathic effects are detrimental structural and biochemical changes viruses induce in host cells, often leading to cell damage or death.
Which of these is an example of a common human disease caused by a virus?
Answer: Common cold
The common cold is a prevalent human illness caused by various viruses, primarily rhinoviruses.
What does 'viral latency' refer to?
Answer: A state where the virus is inactive and dormant within a cell.
Viral latency describes a phase where the virus exists in a dormant state within the host cell, typically without causing active disease symptoms.
Which pathway is mentioned as a common route for virus transmission?
Answer: Ingestion of contaminated food or water
The fecal-oral route, which includes ingestion of contaminated food or water, is a common transmission pathway for many viruses.
What is the key difference between an epidemic and a pandemic?
Answer: A pandemic is a global outbreak, while an epidemic is regional.
A pandemic signifies a widespread epidemic that has crossed international boundaries, affecting a global population, whereas an epidemic is typically localized.
How can certain viruses contribute to the development of cancer?
Answer: By producing proteins that disrupt cell cycle regulation.
Oncogenic viruses can produce proteins that interfere with the host cell's normal regulation of the cell cycle, leading to uncontrolled proliferation.
HIV evades the host's immune system through which strategy?
Answer: Constant mutation of surface proteins to avoid recognition.
HIV frequently mutates its surface proteins, allowing it to evade recognition and destruction by the host immune system.
Which viruses are mentioned as established causes of human cancers?
Answer: Hepatitis B virus (HBV) and Human Papillomavirus (HPV)
Hepatitis B virus (HBV) and certain types of Human Papillomavirus (HPV) are recognized as established causes of human cancers.
What is antigenic drift in influenza viruses?
Answer: The gradual accumulation of point mutations in the genome.
Antigenic drift refers to the minor, gradual changes in viral surface proteins caused by point mutations, leading to new variants.
How do viruses like herpesviruses establish persistent infections?
Answer: By remaining dormant and inactive within host cells (latency).
Herpesviruses establish persistent infections by entering a latent state, where they remain dormant within host cells for extended periods.
What are 'cytopathic effects'?
Answer: Structural and biochemical changes induced by viruses in host cells.
Cytopathic effects are the observable structural and functional alterations that viruses cause in infected host cells.
What are the primary mechanisms by which viruses cause disease?
Answer: By damaging/killing host cells, triggering harmful immune responses, or leading to chronic conditions like cancer.
Viral pathogenesis involves multiple mechanisms, including direct cellular damage, induction of detrimental immune responses, and long-term effects like oncogenesis.
The human body's primary defense against viruses relies exclusively on the adaptive immune system.
Answer: False
The human body employs both innate and adaptive immune systems to defend against viral infections.
RNA interference (RNAi) functions as a mechanism whereby small RNA molecules facilitate the degradation of viral RNA, thereby preventing replication.
Answer: True
RNA interference is a cellular process that targets and degrades viral RNA, serving as a defense against viral replication.
Interferon is a viral protein that facilitates viral replication within host cells.
Answer: False
Interferon is a host-derived protein that signals antiviral defenses to nearby cells; it is not a viral protein that aids replication.
Which component of the human immune system provides a general, non-specific response to viral infections?
Answer: The innate immune system
The innate immune system provides the body's first line of defense with general, non-specific responses to pathogens, including viruses.
What is the function of RNA interference (RNAi) in the context of viral defense?
Answer: To degrade viral RNA and prevent replication.
RNA interference (RNAi) is a cellular mechanism that targets and degrades viral RNA, thereby inhibiting viral replication.
What role does interferon play in the host's defense against viruses?
Answer: It signals nearby cells to enhance their antiviral defenses.
Interferons are signaling molecules that alert neighboring cells to prepare antiviral defenses, helping to limit viral spread.
Vaccines confer immunity through the direct elimination of viruses present within the body.
Answer: False
Vaccines stimulate the immune system to recognize and fight viruses, thereby conferring immunity, rather than directly killing existing viruses.
Nucleoside analogues are antiviral pharmaceuticals that inhibit viral replication by mimicking DNA/RNA precursors and inducing chain termination.
Answer: True
Nucleoside analogues function by being incorporated into viral genetic material, halting replication due to their structural inability to support further chain elongation.
Viruses exert a minor influence on nutrient cycling within aquatic ecosystems.
Answer: False
Viruses play a critical and significant role in nutrient cycling in aquatic ecosystems, particularly through the viral shunt mechanism.
Virotherapy employs genetically modified viruses for the selective destruction of neoplastic cells.
Answer: True
Virotherapy utilizes oncolytic viruses, often genetically engineered, to target and eliminate cancer cells.
Viruses are regarded as simple molecules and possess no utility in nanotechnology.
Answer: False
Viruses are utilized in nanotechnology as natural nanoparticles or scaffolds due to their precise structure and potential for engineering.
Synthetic viruses are generated through naturally occurring mutations within host cells.
Answer: False
Synthetic viruses are created in laboratories by synthesizing viral genetic material from scratch, not through natural mutations.
The 'viral shunt' denotes the process by which viruses release nutrients from lysed microbes into the surrounding environment.
Answer: True
The viral shunt is a key ecological process where viral lysis of microbes releases nutrients, supporting primary production in aquatic ecosystems.
Virovory is the process through which viruses infect host cells.
Answer: False
Virovory refers to the consumption of viruses as a food source, not the process of viral infection.
Reverse transcriptase is an enzyme utilized by viruses to convert their RNA genome into DNA for the purpose of replication.
Answer: True
Reverse transcriptase is essential for retroviruses and other related viruses to synthesize DNA from an RNA template, a key step in their replication cycle.
Phage therapy is a therapeutic modality employing viruses to counteract bacterial infections.
Answer: True
Phage therapy utilizes bacteriophages (viruses that infect bacteria) as a treatment strategy against bacterial infections.
Plant virus particles are utilized as scaffolds in nanotechnology owing to their structural attributes.
Answer: True
The precise and robust structure of plant virus particles makes them suitable for use as natural scaffolds in nanotechnology applications.
The 'viral shunt' mechanism principally entails the direct transfer of genes between bacteria.
Answer: False
The viral shunt primarily involves the release of nutrients from lysed microbes, not direct gene transfer between bacteria.
How do vaccines primarily confer immunity against viral infections?
Answer: By stimulating the immune system to recognize and fight the virus.
Vaccines prepare the immune system by exposing it to viral antigens, enabling a faster and more effective response upon subsequent actual infection.
What is the mechanism of action for nucleoside analogue antiviral drugs?
Answer: They mimic DNA/RNA building blocks, causing chain termination during replication.
Nucleoside analogues are incorporated into the viral genome during replication, leading to premature termination of the DNA or RNA chain.
What is the primary role of viruses in regulating microbial populations in aquatic ecosystems?
Answer: They control populations through infection and lysis.
Viruses regulate microbial populations by infecting and lysing cells, a process critical for nutrient cycling and ecosystem dynamics.
What is virotherapy, a medical application of viruses?
Answer: Using viruses as vectors for gene therapy, especially against cancer.
Virotherapy leverages viruses, often genetically modified, to selectively target and destroy diseased cells, particularly cancer cells, or to deliver therapeutic genes.
In materials science, viruses are utilized primarily as:
Answer: Natural nanoparticles or scaffolds.
The precise structure and size of viruses make them valuable as natural nanoparticles or scaffolds in materials science and nanotechnology.
What does the term 'synthetic virus' typically refer to in a scientific context?
Answer: A virus whose genetic material is synthesized from scratch in a laboratory.
Synthetic viruses refer to those whose genetic material is artificially synthesized in a laboratory setting.
Why are viruses a concern in the context of biological warfare?
Answer: They can cause devastating epidemics and potentially be weaponized.
The potential for viruses to cause widespread epidemics and their amenability to weaponization make them a concern in biological warfare.
The 'viral shunt' is significant in marine environments because it:
Answer: Releases essential nutrients and organic matter from lysed microbes.
The viral shunt process releases dissolved organic matter and nutrients from lysed microbes, supporting primary production in aquatic ecosystems.
What is virovory?
Answer: The consumption of viruses as a food source.
Virovory describes the behavior of consuming viruses as a source of nutrition.
What is the function of reverse transcriptase in viruses like HIV?
Answer: To convert the viral RNA genome into DNA.
Reverse transcriptase is an enzyme that synthesizes DNA from an RNA template, a crucial step for retroviruses like HIV.
Why is phage therapy gaining renewed interest?
Answer: It offers a potential alternative to antibiotics due to rising antibiotic resistance.
The rise of antibiotic-resistant bacteria has spurred renewed interest in phage therapy as a potential alternative treatment.