General Properties of Viruses

Questions and Answers

Which type of virus is most likely to be unstable at 37°C?

Naked icosahedral viruses

Complex viruses

Enveloped viruses (correct)

Naked helical viruses

What temperature range is generally effective in destroying viral infectivity?

40°-50°C

70°-80°C

60°-70°C

50°-60°C (correct)

Which of the following salts is known to stabilize Picornaviruses?

Na2SO4

MgCl2 (correct)

KCl

MgSO4

What is the significance of virus stability in the context of vaccine preparation?

It helps maintain the effectiveness of the vaccine. Signup and view all the answers

Which category of viruses shows variable stability to both heat and cold?

Enveloped viruses Signup and view all the answers

At which pH range are viruses usually stable?

5 to 9 Signup and view all the answers

What happens to enveloped viruses during prolonged storage at -90°C?

They tend to lose infectivity. Signup and view all the answers

Which of the following statements is true regarding naked icosahedral viruses?

They maintain infectivity after several hours at 37°C. Signup and view all the answers

How does lyophilization affect virus preservation?

Some viruses can withstand it and be preserved. Signup and view all the answers

What is a common characteristic of enveloped viruses compared to naked viruses regarding storage?

They lose infectivity more readily during storage. Signup and view all the answers

What is the size range of viruses?

20-300nm Signup and view all the answers

Which of the following is true about the structure of a virus?

Viruses contain a protein coat called the capsid. Signup and view all the answers

Why are viruses considered obligate intracellular parasites?

They cannot grow without living cells. Signup and view all the answers

Which type of organisms can viruses NOT infect?

Fungi Signup and view all the answers

Which statement is true regarding the susceptibility of viruses?

Viruses are susceptible to antimicrobial agents like alcohol. Signup and view all the answers

What component is NOT essential in a virion?

Ribosomes Signup and view all the answers

Which of the following is not a major viral group?

Fungal viruses Signup and view all the answers

What is a key reason why antibiotics are ineffective against viruses?

Viruses do not have a cell wall. Signup and view all the answers

What forms the genetic material of viruses?

Both DNA and RNA Signup and view all the answers

Which function of the capsid is vital for protecting the viral nucleic acid?

Protecting from damage Signup and view all the answers

What term describes the protein subunits that make up the viral capsid?

Capsomeres Signup and view all the answers

Which of the following enzymes is NOT classified under viral proteins?

Neuraminidase Signup and view all the answers

Which statement about the viral envelope is true?

It consists of a bilayer membrane containing glycoproteins and lipids. Signup and view all the answers

What is the size range of most viruses?

20-300 nm Signup and view all the answers

What type of viruses typically exhibit a rod-shaped morphology?

Plant viruses Signup and view all the answers

Which viral component does NOT contribute to the virion's antigenicity?

Nucleic acid Signup and view all the answers

Which type of symmetry is typically conferred by the viral capsid?

Structural symmetry Signup and view all the answers

Which of the following is a function of viral glycoproteins?

Facilitating attachment to host cells Signup and view all the answers

What structural characteristic is used to identify different viruses?

Appearance of capsomers Signup and view all the answers

Which treatment is most effective in disabling viruses due to their lipid envelope?

Ether Signup and view all the answers

What is the primary reason why antibiotics are ineffective against viruses?

Antibiotics are designed for bacterial infections Signup and view all the answers

What characteristic of a virus's genome makes it more susceptible to inactivation by agents like formaldehyde?

Single-stranded genome Signup and view all the answers

Which method is most suitable for sterilizing surfaces exposed to viruses?

High-energy particles Signup and view all the answers

Naked viruses have resistance to which of the following conditions?

Extreme pH and temperature Signup and view all the answers

What is the primary role of non-ionic detergents concerning viruses?

Solubilize lipid constituents of viral membranes Signup and view all the answers

Which disinfectant is mentioned as effective against certain viruses when used in concentrations of 50-70%?

Alcohol Signup and view all the answers

What phenomenon allows vital dyes to inactivate viruses?</A>

Binding to nucleic acids Signup and view all the answers

What characteristic of anionic detergents contributes to virus disruption?

They disrupt capsids into separate polypeptides Signup and view all the answers

What is a common mode of transmission for naked viruses?

Fecal-oral route Signup and view all the answers

Which mechanism allows SARS-CoV-2 to enter host cells?

S protein binding to ACE2 receptor and membrane fusion Signup and view all the answers

What is the primary target tissue for SARS-CoV-2 infection?

Alveolar epithelial cells in the respiratory tract Signup and view all the answers

Which of the following is NOT a non-pharmaceutical intervention for COVID-19 prevention?

Vaccination with mRNA vaccines Signup and view all the answers

Which structural protein is responsible for the attachment of SARS-CoV-2 to host cells?

Spike protein (S) Signup and view all the answers

What type of virus is SARS-CoV-2 classified as?

Positive-sense ssRNA virus Signup and view all the answers

Which of the following transmission modes involves respiratory droplets?

Aerosol transmission from coughing Signup and view all the answers

Study Notes

General Characteristics of Viruses

Unique infectious agents, smallest in size (20-300 nm).
Non-cellular, with a nucleic acid core of either DNA or RNA.
Encased in a protective protein coat called capsid for attachment and entry.
Obligate intracellular parasites; capable of growth only within living cells.
Lack ribosomes and metabolic enzymes; depend on host cellular resources for reproduction.
Not affected by antibiotics due to absence of cellular structures; susceptible to antimicrobial agents like alcohol and chlorine.
Infect a range of organisms including unicellular prokaryotes and eukaryotes.

Major Viral Groups

Plant viruses.
Insect viruses.
Bacteriophages (viruses infecting bacteria).
Animal viruses (viruses infecting vertebrates).

Virus Structure

Virion consists of at least DNA or RNA and capsid.
Capsid made of protein subunits called capsomeres; unique arrangement aids in viral identification.
Capsid functions include protection, cell attachment, structural symmetry, and antigenicity.

Viral Proteins and Enzymes

Common enzymes: polymerase, integrase, reverse transcriptase.
Envelope lipids are derived from the host cell, forming a lipid membrane around the virus.
Viral envelope contains glycoproteins like neuraminidase and hemagglutinin, aiding in attachment and release of new viral particles.

Viral Envelope

Formed during replication; contains glycoproteins and lipids.
Protects nucleic acid, facilitates attachment, enhances structural integrity, and provides antigenic variability.

Morphology of Virions

Smallest among microorganisms, typically measured in nanometers.
Size varies significantly between virus types (e.g., picornaviruses vs. poxviruses).
Morphological classification: naked icosahedral, enveloped icosahedral, naked helical, enveloped helical, and complex viruses.

Viral Stability

Stability varies with factors like temperature; naked viruses are more heat-stable than enveloped viruses.
Heat inactivation occurs at 50°-60°C; preservation strategies involve sub-zero storage.
Salts can stabilize certain viruses, affecting vaccine development and efficacy.
pH effects: stability generally between pH 5-9; extreme acidity or alkalinity can destroy viruses.

Modes of Physical and Chemical Inactivation

Ether and detergents disrupt lipid envelopes and capsids effectively.
Formaldehyde inactivates viral infectivity through nucleic acid reaction.
Antimicrobial agents such as chlorination and alcohols are necessary to eliminate viruses.

Transmission of Viruses

Depend on the source and route to target tissue; naked viruses endure drying and extreme conditions.
Direct transmission through respiratory droplets; indirect through contaminated surfaces.
Aerosol transmission involves small particles remaining airborne.

SARS-CoV-2 Specifics

Causative agent of COVID-19; enveloped, positive-sense, single-stranded RNA virus.
Attach to host cells via spike protein binding to ACE2 receptors; fusion allows entry.
Primary target is the respiratory tract; other targets include the gastrointestinal tract.

Prevention Strategies for COVID-19

Vaccination options include mRNA (Pfizer-BioNTech, Moderna), viral vector (AstraZeneca, Johnson & Johnson), and inactivated virus vaccines (Sinopharm, Sinovac).
Non-pharmaceutical interventions: wearing masks, hand hygiene, physical distancing, and proper ventilation.

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Description

Explore the unique characteristics of viruses in this quiz. Learn about their structure, sizes, and the role they play as obligate intracellular parasites. Test your knowledge on what makes these infectious agents distinct from other microorganisms.