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Questions and Answers
What is a defining characteristic of viruses?
What is a defining characteristic of viruses?
- They have complex cellular organelles.
- They are obligate intracellular pathogens. (correct)
- They can replicate independently of host cells.
- They are visible with a light microscope.
Which component of a virus is responsible for providing protection and facilitating attachment?
Which component of a virus is responsible for providing protection and facilitating attachment?
- Nucleic acid
- Lipoprotein envelope (correct)
- Capsomeres
- Viral glycoproteins
Which of the following best describes the structure of a virus particle?
Which of the following best describes the structure of a virus particle?
- A complex of RNA, proteins, and carbohydrates.
- A single cellular organism with organelles.
- A nucleocapsid possibly surrounded by an envelope. (correct)
- A robust cell wall and a nucleus.
How are viruses classified?
How are viruses classified?
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What type of viruses are not typically acquired by animals?
What type of viruses are not typically acquired by animals?
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Which method is commonly used for cultivating animal viruses?
Which method is commonly used for cultivating animal viruses?
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What type of nucleic acid can be found in viruses?
What type of nucleic acid can be found in viruses?
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What characteristic makes viruses highly specific in their host interactions?
What characteristic makes viruses highly specific in their host interactions?
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Which statement regarding the self-replication of viruses is correct?
Which statement regarding the self-replication of viruses is correct?
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What is the size range of most viruses?
What is the size range of most viruses?
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Study Notes
Overview of Virology
- Virology is the study of viruses and a subfield of microbiology.
- Viruses are obligate intracellular pathogenic agents that cannot grow outside living cells.
Characteristics of Viruses
- Size: Range from 10 to 400 nm; invisible to light microscopes but detectable with electron microscopes.
- Structure: Composed of a nucleic acid genome (DNA or RNA) and a protein coat; may have a lipoprotein envelope.
- Obligate Intracellular: Require living cells for replication, cannot be cultivated in artificial media.
- Self-Replication: Infect host cells and utilize the host's machinery to produce new virus particles.
- Specificity: Highly specific to host and cell type; e.g., plant viruses do not infect animals, and strains targeting one organ are often ineffective on another.
Propagation Methods
- Animal Viruses: Propagated using tissue cultures, chicken embryonated eggs, or experimental animals.
- Plant Viruses: Propagated in living plants or plant cell cultures.
- Bacteriophages: Cultured in bacterial cultures.
Virus Structure
- Virion: Complete virus particle consisting of a genome, capsid, and possibly an envelope.
- Genome: Can be DNA or RNA, arranged in linear, circular, or segmented forms; may be single or double-stranded.
- Capsid: Protein coat protecting the genome, made of capsomeres, with potential shapes including spherical, helical, or complex; plays a role in viral attachment and antigenicity.
- Nucleocapsid: Combined structure of nucleic acid and capsid.
- Envelope: Lipoprotein layer derived from host cell membranes, modified with viral glycoprotein spikes; more common in animal viruses than in plant viruses, important for attachment.
Virus Classification
- Viruses are classified based on:
- Morphology
- Nucleic acid type
- Mode of replication
- Host organism
- Type of disease caused
- Major categories include:
- Animal viruses
- Plant viruses
- Fungal viruses
- Bacterial viruses (Bacteriophages)
Viral Replication
- Entirely dependent on host cells for replication; replication strategies vary among virus types but generally follow a similar series of events.
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