40 Questions
What is the temperature range that can generally inactivate heat?
56-60°C for 30 minutes
What is the pH range that can destroy most viruses?
pH below 5 and alkaline pH above 9
What is unique about the glycerol's effect on viruses and bacteria?
Bacteria are destroyed by 50% glycerol, while viruses survive
What type of agents are most effective against viruses?
Oxidizing agents
What is the main characteristic that distinguishes viruses from bacteria in terms of reproduction?
Complex reproductive processes
What is the composition of a virion?
DNA or RNA and a protein shell
How are viruses classified based on their host specificity?
Bacteria, animal, and plant viruses
What is the definition of virology?
The branch of microbiology concerned with viruses and viral diseases
What is the term for the entire infectious unit of a virus?
Virion
What is essential for a virus to replicate?
A host cell
What is the function of the capsid?
To encase and stabilize the viral nucleic acid
What is the effect of viral antiserum on the virion?
It neutralizes the virion
What is a characteristic of viruses?
They can infect a wide range of organisms, from unicellular to multicellular
What is the result of treating viral nucleic acid with ribo- or deoxyribonuclease?
It is hydrolyzed
What is a by-product of the viral replicative cycle?
Empty capsids
What is missing from all viruses?
An ATP-generating system
What is the primary reason why large viruses of the pox group can be seen using ordinary light microscopes?
Due to the use of staining procedures
What is the purpose of mixing a virus suspension with a suspension of polystyrene latex particles of known concentration in electron microscopy?
To count the number of virus particles in the suspension
What is responsible for the increased limit of resolution in electron microscopes compared to light microscopes?
The shorter wavelength of high-velocity electrons
What is the primary application of the fluorescent antibody technique in virology?
To demonstrate viral antigens in tissues
What is the function of structured proteins in viruses?
To have several important functions
What is the minimum diameter of virus particles that can be resolved by electron microscopes?
Less than 1 nm
What is the advantage of using electron microscopes over light microscopes in virology?
Electron microscopes have a higher limit of resolution
What can be recognized using the fluorescent antibody technique and electron microscopy in infected animals or humans?
Characteristic histological and cytological changes
What is the primary function of the structural proteins of a virus?
To protect the viral genome against inactivation by nucleases
How can the structural proteins of a virus be studied?
By dissociating the proteins of the virus particle with a detergent and then separating them by electrophoresis through polyacrylamide gel matrix
What type of nucleic acid do most major families of RNA-containing animal viruses have?
Single-stranded RNA
Which of the following viruses is an exception to the rule that DNA-containing animal viruses have double-stranded DNA genomes?
Parvovirus
What is the function of the enzyme reverse transcriptase in RNA tumor viruses?
To make a DNA copy of virus RNA
What is the purpose of the protein hemagglutinin in influenza virus?
To attach to susceptible cells
How can the type of nucleic acid and strandedness be determined?
By staining with acridine orange and identifying the nucleic acid by color reaction and enzyme digestion tests
What is a characteristic of the structural proteins of many viruses?
They are very specialized molecules designed to perform a specific task
Which virus causes cytomegalic inclusion disease?
Cytomegalovirus
What is the characteristic of Poxviridae family?
Contain double-stranded DNA genome
Which virus is associated with several human malignancies?
EB virus
What is the characteristic of Picornaviridae family?
Contain single-stranded RNA genome
Which virus is the most common cause of colds in humans?
Rhinovirus
What is the characteristic of Reoviridae family?
Contain double-stranded RNA genome
Which virus is an agent of infantile gastroenteritis?
Rotavirus
What is the characteristic of Varicella-zoster virus?
Causes zoster and chickenpox
Study Notes
Characteristics of Viruses
- Viruses are inactivated by temperatures of 56-60°C for 30 minutes
- pH affects viral survival, with most viruses destroyed at pH below 5 and above 9
- Glycerol affects viruses and bacteria differently, with 50% glycerol surviving most viruses but destroying bacteria
- Bactericidal agents, such as Phenol, are not efficient as viral disinfectants, whereas oxidizing agents are most effective against viruses
- Antibiotics and chemotherapeutic agents, like Sulfonamides, penicillin, streptomycin, and tetracyclines, have little effect on viruses
Reproductive Processes
- Viral reproductive processes differ from bacterial binary fission
- Viruses contain only one kind of nucleic acid, which is covered by a protein coat
Definition of Virology
- Virology is the branch of microbiology that deals with viruses and viral diseases
Nature of Viruses
- Viruses are minute infectious agents that are not resolved in the light microscope
- They lack independent metabolism and replicate only within living host cells
- They have genetic continuity and the possibility of mutation
- They are morphologically heterogeneous, occurring as rod-shaped, spherical, or polyhedral forms
- Viruses are composed of a nucleic acid (the nucleoid), DNA or RNA (but not both), and a protein shell or capsid
- The protein shell contains and protects the nucleic acid
- Viruses are classified according to host specificity, origin, mode of transmission, or the manifestation they produce
Viral Structure
- The individual particle or virion consists of nucleic acid and a protein shell or capsid
- Capsid: a symmetric protein shell that encloses the nucleic acid genome
- Nucleocapsid: the capsid together with enclosed nucleic acid
- A virion lacks certain components essential for its replication and must depend on the host cell for these missing factors
- One component missing from all viruses is an ATP-generating system
Microscopy
- Although most viruses cannot be seen by ordinary microscopic methods, the light microscope has some important applications in virology
- Large viruses of the pox group can be demonstrated by staining procedures
- The fluorescent antibody technique is valuable for demonstrating viral antigens in tissues
- Electron microscopy has brought even the smallest viruses into visible range and is capable of resolving particles with diameters of less than 1 nm
Chemical Composition of Viruses
- Viral Protein: serves to protect the viral genome, participate in attachment to susceptible cells, and determines the antigenic characteristics of the virus
- Virus structural proteins may be very specialized molecules designed to perform specific tasks
- Viral Nucleic Acid: contains a single kind of nucleic acid, either DNA or RNA, that encodes the genetic information necessary for the replication of the virus
- Viral Lipids: some viruses contain lipids as part of their structure
Virus Families
- Poxviridae Family: relatively large, brick-shaped or ovoid viruses containing a double-stranded DNA genome and protein, enveloped by double membranes
- Picornaviridae Family: small, ether-resistant viruses that contain single-stranded RNA
- Reoviridae Family: ether-resistant viruses that contain double-stranded RNA
This quiz assesses your understanding of the factors that affect the survival of viruses, including heat, pH, glycerol, and various disinfectants. Test your knowledge of microbiology and virology concepts.
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