Virology Quiz

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Questions and Answers

What is the characteristic of virion morphology that is used in virus classification?

Mode of transmission

Type of nucleic acid

Shape and size of the virion (correct)

Number of proteins

What type of viruses have complex structures?

Rabies virus

Poxviruses (correct)

Bacteriophage (correct)

All of the above

What is the function of the viral capsid proteins in the attachment process?

To transcribe nucleic acid

To release the virus from the cell

To bind to specific receptors on the host cellular surface (correct)

To synthesize proteins

What occurs after the penetration of the virus into the host cell?

Uncoating and transcription Signup and view all the answers

What is the result of the fusion of viral and cellular membranes during attachment?

Viral entry Signup and view all the answers

What is the term for the process of a virus entering the host cell through receptor-mediated endocytosis?

Receptor-mediated endocytosis Signup and view all the answers

What is the term for the 'growth cycle' of a virus?

Viral replication Signup and view all the answers

What is a characteristic of viruses that is used in their classification?

All of the above Signup and view all the answers

What is the size range of viruses?

20-300 nanometer Signup and view all the answers

What type of nucleic acid do viruses contain?

Either DNA or RNA Signup and view all the answers

What is the main component of a virus particle?

Nucleic acid surrounded by a protein coat Signup and view all the answers

What do viruses lack?

Mitochondria and ribosomes Signup and view all the answers

How do viruses replicate?

Through replication of their nucleic acid and synthesis of viral protein Signup and view all the answers

Can viruses multiply in media?

No, viruses do not multiply in media Signup and view all the answers

What is the typical size of viruses?

20-300 nm Signup and view all the answers

What type of nucleic acid is found in bacteria?

DNA and RNA Signup and view all the answers

What is the function of the capsid in a virus?

To protect the nucleic acid Signup and view all the answers

What is the term for the complete infectious virus particle?

Virion Signup and view all the answers

What is the symmetry of viruses that cause yellow fever?

Icosahedral symmetry Signup and view all the answers

What is the main difference between enveloped and naked viruses?

The presence of a lipid membrane Signup and view all the answers

Why are viruses sensitive to antibiotics?

They are not sensitive to antibiotics Signup and view all the answers

What is the term for the protein coat that surrounds the nucleic acid?

Capsid Signup and view all the answers

Study Notes

Virology

Virology is a branch of science that deals with viruses and viral diseases.
Viruses are the smallest infectious agents and are obligate intracellular parasites.

General Properties of Viruses

Viruses are smaller than bacteria, ranging in size between 20-300 nanometers.
Viruses contain only one type of nucleic acid, either DNA or RNA, but never both.
Viruses consist of nucleic acid surrounded by a protein coat, and some have additional lipoprotein envelope.
Viruses lack cellular organelles, such as mitochondria and ribosomes.
Viruses are obligate cellular parasites, replicating only inside living cells.
Viruses replicate through replication of their nucleic acid and synthesis of viral protein.
Viruses do not multiply in media.
Viruses do not undergo binary fission.

Comparison between Viruses and Bacteria

Viruses have a size range of 20-300 nm, while bacteria have a size of 1000 nm.
Viruses have DNA or RNA, but not both, while bacteria have both DNA and RNA.
Viruses have an envelope present in some, while bacteria have a cell wall.
Viruses do not multiply by binary fission, while bacteria do.
Viruses are sensitive to antibiotics, while bacteria are not.
Viruses grow only in the living host cell, while bacteria grow in culture media.

Viral Structure

Viruses are composed of nucleic acid (DNA or RNA) surrounded by a protein coat called the capsid.
The capsid is composed of small structural units called capsomeres.
The capsid protects nucleic acid from inactivation by outer physical conditions.
The complete infectious virus particle is called a virion.
The basic virus structure is DNA or RNA + capsid protein = nucleocapsid = naked virus.

Types of Symmetry of Virus Particles

Viruses are divided into three groups based on the morphology of the nucleocapsid and arrangement of capsomeres:
- Icosahedral (Cubic) symmetry
- Helical symmetry
- Complex structures

Classification of Viruses

Classification of viruses is based on the following characteristics:
- Virion morphology, including size, shape, type of symmetry, presence or absence of envelope
- Virus genome properties, including type of nucleic acid, size of genome strand, linear or circular, positive or negative
- Virus protein properties, including number, size, functional activities, amino acid sequences, and reverse transcriptase
- Biological properties, including natural host range, mode of transmission, vector relationships, pathogenicity, tissue tropisms

Viral Replication

As obligate intracellular parasites, viruses must enter and replicate in living cells to "reproduce" themselves.
The "growth cycle" involves specific attachment of virus, penetration and uncoating, nucleic acid transcription, protein synthesis, maturation and assembly of virions, and release from the cell by lysis.
The typical infectious cycle consists of:
- Attachment: specific binding between viral capsid proteins and specific receptors on the host cellular surface
- Penetration: follows attachment, involving receptor-mediated endocytosis in non-enveloped viruses or membrane fusion in enveloped viruses
- Uncoating: release of viral genome from the capsid
- Transcription and Translation: synthesis of viral protein and genome replication
- Assembly: formation of new virions
- Release: release of new virions from the cell by lysis