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Questions and Answers
Which type of virus has a DNA intermediate in its life-cycle?
What defines ssRNA-RT viruses?
Which group is an example of (-)ssRNA viruses?
Which of the following viruses has RNA as its genome and an RNA intermediate?
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What is a characteristic feature of Retroviruses?
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Which type of virus contains double-stranded DNA?
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Which of the following viruses is considered a double-stranded RNA virus?
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Which category of viruses includes Parvoviruses?
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What type of virus is classified as single-stranded RNA?
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Which of the following viruses is a double-stranded DNA virus?
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What is the primary defining characteristic of viruses?
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Which part of a virus is responsible for its genetic information?
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What classification system is used to categorize viruses according to the International Committee on Taxonomy of Viruses?
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Which of the following is a characteristic of non-living viruses?
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According to the Baltimore classification, which groups are viruses divided into?
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What does the term 'Virology' refer to?
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What did Ivanowsky discover in 1892 regarding the cause of the tobacco plant disease?
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What name did Ivanowsky give to the agent causing the disease he studied?
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Which scientist confirmed the existence of viruses in 1898?
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What was the significant achievement of Stanley in 1935?
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How are viruses different from cells, as discovered by Stanley?
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What phenomenon did the disease cause on the tobacco plant leaves, as described?
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What year was the first electron microscope invented, enabling the visualization of viruses?
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How did Ivanowsky demonstrate the disease's transference to healthy plants?
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What was the original meaning of the word 'virus' in Latin?
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What is the maximum size that viruses can attain?
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How do viruses multiply within a host organism?
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Which of the following statements about viruses is TRUE?
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Which component is NOT typically found in a virus structure?
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What classification system divides viruses based on their genetic material?
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Which of the following best describes the nature of viruses?
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What happens to viruses outside their host cells?
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How can viruses affect living organisms?
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What is the role of the viral envelope?
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Which property differentiates viruses from living organisms?
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Which of the following statements regarding viral classification is accurate?
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What is a defining feature of an enveloped virus?
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Why aren't antibiotics effective against viruses?
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Which of the following statements correctly describes the nature of viral replication?
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Study Notes
Virology: An Introduction
- Virology is the study of viruses, their properties (physical, chemical, and biological), the diseases they cause in humans, animals, plants, and other organisms, and how to control or utilize them.
- The word "virology" comes from the Latin word "virus," meaning poison.
Historical Overview
- In 1892, Ivanowsky suggested the existence of viruses while researching tobacco mosaic disease. He found the disease agent was smaller than bacteria and passed through bacterial filters.
- Beijerinck confirmed this in 1898.
- In 1935, Stanley isolated the Tobacco Mosaic Virus (TMV) chemically as crystals, and its structure was later revealed using the electron microscope (invented in the 1930s). The first electron microscope images of viruses were obtained in 1931 by Ernst Ruska and Max Knoll.
Defining Viruses
- Various definitions exist, including: an obligate intracellular parasite smaller than 200 nm (Lwoff, 1959); submicroscopic infectious agents that reproduce only inside cells (Baud, 1964).
- Viruses are smaller than bacteria.
- Viruses are only seen using an electron microscope and are acellular (lacking a cellular structure).
Characteristics of Viruses
- Viruses exist in all environments.
- Viruses exhibit characteristics of both living and non-living things.
- They resemble non-living things in their inability to respire, feed, excrete, and their capacity for crystallization; they lack independent metabolic activity outside of a host cell. Viruses cannot be cultivated in artificial media.
- Viruses have a constant shape, size, and molecular weight that don't change.
- Conversely, viruses resemble living organisms by infecting living organisms, causing diseases, reproducing, and undergoing mutations.
- Key characteristics distinguishing viruses: extremely small size (visible only with an electron microscope); obligate intracellular parasites (relying on host cells for replication); often specialized in parasitism (infecting specific hosts); non-motile; lacking ribosomes; composed of one type of nucleic acid (DNA or RNA), a protein coat (capsid), and sometimes a lipid envelope; acellular; replication dependent on their genetic material; metabolically inactive outside a host cell ("virus particle" vs. "virion"); cultivable only in living host cells; capable of mutation; variable tolerance to high temperatures; unaffected by antibiotics.
- Viral infection can produce inclusion bodies (in the cytoplasm or nucleus of host cells).
Viral Structure
- Viruses consist of two or three parts: a nucleic acid (genome—DNA or RNA), a protein coat (capsid) that protects the genome and aids in attachment to host cells, and sometimes a lipid envelope (present in some viruses) containing glycoproteins that aid in host cell attachment.
Viral Size
- Viruses vary in size (measured in nanometers), ranging from 20-300 nm and are thus only visible with an electron microscope. Size categories: large (200-300 nm), medium (75-150 nm), and small (20-30 nm).
Viral Classification
- Viral classification is complex. The International Committee on Taxonomy of Viruses (ICTV) developed a system using order (-virales), family (-viridae), subfamily (-virinae), genus (-virus), and species.
- The Baltimore classification system categorizes viruses into seven classes based on their genome type (DNA or RNA), replication method, and transcription method.
Baltimore Classification Groups
- dsDNA viruses
- ssDNA viruses
- dsRNA viruses
- (+)ssRNA viruses
- (−)ssRNA viruses
- ssRNA-RT viruses
- dsDNA-RT viruses
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Description
Explore the fascinating field of virology, including the properties of viruses and their impact on various organisms. This quiz also delves into key historical milestones in virus research, from Ivanowsky's early discoveries to the advancements made with electron microscopy. Test your knowledge on definitions and significant figures in virology.
