Basic Virology

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Questions and Answers

What type of nucleic acid can viruses contain?

Only DNA

Only RNA

Both DNA and RNA simultaneously

Either DNA or RNA, but not both (correct)

Which characteristic is NOT true for viruses?

Viruses have a lipid membrane envelope.

Viruses lack cellular structures.

Viruses can perform binary fission. (correct)

Viruses are infectious particles.

What is the primary function of a virus's capsid?

To facilitate the movement of the virus

To protect the viral nucleic acid (correct)

To provide energy for the virus

To aid in the replication of viral DNA

Which of the following is a characteristic of prions?

Composed only of proteins Signup and view all the answers

What distinguishes viroids from typical viruses?

Viroids have a nucleic acid structure consisting of RNA only. Signup and view all the answers

Which of the following shapes can viruses take?

Helical and polyhedral Signup and view all the answers

What is the role of spikes on a virus?

To aid in attachment to host cells Signup and view all the answers

In what way are defective viruses different from typical viruses?

Defective viruses cannot replicate on their own. Signup and view all the answers

Which characteristic is true of bacteria but NOT of viruses?

Presence of a cell wall Signup and view all the answers

What is the size range of the largest viruses compared to bacteria?

Approximately the same size as the smallest bacterial cells Signup and view all the answers

What process occurs when a bacteriophage infects a bacterium?

The bacteriophage multiplies and releases new virions. Signup and view all the answers

Which of the following is not a method of growing viruses?

Cultivating viruses in a nutrient broth. Signup and view all the answers

Which of the following describes the lysogenic cycle of viral replication?

The viral DNA integrates into the host genome and remains dormant. Signup and view all the answers

Which of the following is a cellular change that can occur in an infected cell?

Death of the cell. Signup and view all the answers

What is the primary outcome of the immune response in a viral infection?

Elimination of infected cells and virions. Signup and view all the answers

What distinct levels does viral pathogenesis encompass?

Cellular changes and effects on the infected patient. Signup and view all the answers

What type of change is typically associated with malignant transformation in an infected cell?

Uncontrolled cell growth. Signup and view all the answers

Which of the following is not a method by which a virus can persist in a host?

Mutation. Signup and view all the answers

What occurs during the transmission phase of viral pathogenesis?

The virus enters the host and begins to spread. Signup and view all the answers

Which process is not typically formed in cells infected by viruses?

Normal cell division. Signup and view all the answers

Study Notes

Viruses: Invisible Invaders

Viruses are infectious particles that are not cells.
They are obligate intracellular parasites, meaning they need living cells to replicate.
Viruses can infect all types of organisms, including animals, plants, and bacteria.

Life Without the Basics

Unlike cells, they lack certain characteristics like enzymes and organelles.
Viruses can contain either DNA or RNA as their genetic material, but never both.
They are insensitive to antibiotics, unlike bacteria.

Viral Structure and Shape

Viruses come in a variety of shapes, including polyhedral (many-sided), helical (rod-shaped), and combinations of both.
The smallest virus is about 20 nanometers (nm), while the largest can be as big as a small bacterial cell.

The Heart of the Virus: The Nucleic Acid

Viruses carry their genetic material as either DNA or RNA.
This nucleic acid can be single-stranded or double-stranded and linear or circular.
DNA is always a single molecule, but RNA can exist as a single molecule or multiple pieces.

The Protective Coat: Capsid and Envelope

The nucleic acid is enclosed within a protein coat called the capsid.
The capsid is made up of subunits called capsomeres, which determine the virus's geometric shape.
Some viruses have an additional protective layer called an envelope, which is a membrane derived from the host cell.
Viral envelopes often contain projections known as spikes, which are glycoproteins that help the virus attach to host cells.

Atypical Viruses: When things get strange

Defective viruses require a "helper" virus to provide missing functions for replication.
Pseudo-virions are formed during infection, incorporating host cell DNA into the capsid protein.
Viroids are infectious agents consisting solely of circular RNA without a protein coat; they primarily affect plants.
Prions are infectious protein particles that are resistant to various treatments and are responsible for fatal neurodegenerative diseases.

The Growth of Viruses: A tale of infection

Bacteriophages (viruses that infect bacteria) can be studied in the lab by mixing them with host bacteria and melted agar.
Animal viruses can be grown in laboratory animals or by injecting them into embryonated eggs.

The Viral Growth Curve: From attachment to release

Viral growth is characterized by a specific curve, showing stages of attachment, penetration, viral synthesis, assembly, maturation, and release.

Viral Replication: The Cycle of Life

Lytic Cycle: Virus replicates rapidly, killing the host cell and releasing new viruses.
Lysogenic Cycle: Virus integrates its DNA into the host cell's DNA, remaining dormant and replicating with the host cell for several generations.

Viral Pathogenesis: The Story of Disease

Viral diseases can be understood at two levels: changes within infected cells and processes in the infected patient.
Cellular effects include cell death, fusion into multinucleated giant cells (syncytia), formation of inclusion bodies, malignant transformation, and sometimes no visible changes.
Viral pathogenesis in the patient involves transmission, replication, spread to other cells and organs, immune response, and sometimes persistence in the form of chronic, latent, or slow virus infections.