14 Questions
What is the primary function of the capsid in a virus?
To protect the NA and stimulate immune response
What is the characteristic of viruses that makes them resistant to antibiotics?
Their lack of metabolic activity
What is the typical size range of viruses?
20-300 nm
Which of the following viruses has a helical symmetry?
Influenza virus
What is the purpose of the envelope in a virus?
To facilitate attachment to host cell receptors
Which type of virus is sensitive to lipid solvents disinfectants?
Enveloped viruses
What is the characteristic of prions?
They are protein agents without detectable NA
Why are viruses typically cultured on living cells?
Because they lack metabolic activity
What type of diseases do slow viruses cause in man and animal?
Slow virus disease characterized by CNS manifestations with gradual onset and fatal progressive course
What is the characteristic feature of viroids?
RNA without a protein coat
What is the role of HBV surface antigen in the replication of HDV?
It provides a coat for HDV to replicate
What is the characteristic feature of pseudoviruses?
Cellular DNA is incorporated into the viral capsid
What is the significance of inclusion bodies in the identification of viruses?
They are used for diagnosis of viral infections
What type of inclusion bodies are seen in the brain of rabid animals?
Negri bodies
Study Notes
Viruses
- Viruses are the smallest infectious agents in nature, capable of infecting humans, animals, plants, insects, or bacteria.
Differences between Viruses and Bacteria
- Viruses are small in size
- Contain only a single Nucleic acid (NA), either DNA or RNA
- Have no metabolic activity (e.g., no ribosomes for protein synthesis)
- Are obligatory intracellular (replicate only inside the cell)
- Are not affected by antibiotics
- Cannot grow on artificial media and are cultured only on living cells (e.g., tissue culture)
Size of Virus
- Measure in nanometers (nm), with sizes ranging from 20-300 nm
- Can pass through bacterial filters and are seen only by an electron microscope (EM)
Structure of the Virus
- NA core (DNA or RNA): the infective part of the virus, can be single or double stranded
- Capsid: a protein coat that surrounds the NA, formed of several capsomeres
- Capsid symmetry: can be cubic or icosahedral, helical, or complex
- Functions of capsid: responsible for viral symmetry, protection of NA, antigenicity, and adsorption to host cell
- Envelope: a lipoprotein present outside the capsid in some viruses, responsible for adsorption to host cell receptors
Atypical Viruses
- Prions: protein agents without detectable NA, cause slow virus diseases with CNS manifestations
- Viroids: RNA without a protein coat, affect plants
- Defective Viruses: have a mutation that makes them unable to synthesize their own capsid protein, require the help of another virus to replicate
- Pseudoviruses: cellular DNA incorporated into viral capsid, can infect a cell but cannot replicate
Inclusion Bodies (IBs)
- Definition: collection of virus particles (or viral protein) inside the cell, visible by light microscope with certain stains
- Significance: used in the identification of some viruses
- Types of IBs:
- Non-viral: intracytoplasmic basophilic, e.g. in Chlamydia
- Viral:
- Intracytoplasmic acidophilic: e.g. in Rabies (Negri bodies), Smallpox (Guarnieri bodies)
- Intranuclear: e.g. in Yellow fever (Torres bodies), Polio, Herpes simplex, Adenovirus
- Both Intracytoplasmic and Intranuclear: e.g. in measles and CMV
Compare and contrast the characteristics of viruses and bacteria, including their size, nucleic acid content, metabolic activity, and response to antibiotics.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
