Virus Structure and Classification Quiz

A virus is a tiny infectious agent that needs a host cell to reproduce. It's made up of two main parts: genetic material (RNA or DNA) and a protective protein coat called a capsid.

A virion is a complete, infectious virus particle. It consists of a viral genome (DNA or RNA) encased in a protein coat (capsid). Some viruses also have a lipid envelope surrounding the capsid.

Viruses are much smaller than the cells they infect. The smallest viruses are about 20nm in diameter, while the largest ones can be up to 300nm. This size difference allows viruses to pass through bacterial filters.

Viruses can be classified into families based on their genetic material (RNA or DNA), replication strategy, capsid symmetry (helical or icosahedral), and presence or absence of an envelope.

The pathogenicity of a virus, or how harmful it is, can vary greatly even within closely related virus species. This means different viruses within the same group can cause different diseases.

Viruses are obligate intracellular parasites, meaning they require a living host cell to replicate. They cannot reproduce on their own.

The viral genome contains the genetic instructions for making new virus particles. It's the blueprint for building more viruses inside infected cells.

The capsid provides the virus with structural support and protects its delicate genome. It also helps the virus attach to and enter host cells.

The most common types of viral genomes are single-stranded RNA (ssRNA) and double-stranded DNA (dsDNA).

Single-stranded RNA genomes are further classified as positive polarity (messenger RNA sense) or negative polarity (antisense).

Positive-strand RNA viruses can be directly translated into proteins, while negative-strand RNA viruses require an intermediate step.

The protein shell that encloses the viral genome is called the capsid.

Most virus families exhibit either helical or icosahedral capsid symmetry.

Helical capsids are made up of repeating units of a single polypeptide type, forming a helical cylinder.

Icosahedral capsids are more complex, composed of several different polypeptides arranged into subassemblies called capsomers.

The viral nucleic acid is contained within the empty space created by the rigid, icosahedral structure.

A protective membrane surrounding the nucleocapsid of some viruses. It's derived from the host cell membrane but has virus-specific proteins.

Viruses without an envelope are referred to as naked viruses.

The Baltimore classification groups viruses based on their genome type and replication strategy.

The smallest, non-enveloped icosahedral viruses. They have double-stranded circular DNA.

The process by which viruses replicate inside host cells. It involves steps like attachment, penetration, gene expression, assembly, and release.

The central core of a virus containing its genetic material (DNA or RNA).

The largest, complex viruses with linear, double-stranded DNA. They are enveloped and have a brick-like shape.

The process by which a virus's genetic material enters a host cell. The cell absorbs the virus, or the virus injects its genetic material.

A family of naked, icosahedral viruses, they are among the smallest RNA viruses. They feature a single-stranded, linear, nonsegmented, positive-polarity RNA within a capsid. Their name derives from 'pico' for small and RNA-containing.

Enveloped viruses with an icosahedral nucleocapsid and double-stranded linear DNA. They are known for causing latent infections. Five important human pathogens are herpes simplex 1 & 2, varicella-zoster virus, cytomegalovirus, and Epstein-Barr virus.

Double-shelled viruses (42nm in diameter) with an icosahedral capsid covered by an envelope. Their DNA is a double-stranded circle with one strand incomplete. Hepatitis B virus is a prime example.

The largest viruses, with a bricklike shape, an envelope with an unusual appearance, and complex capsid symmetry. They are named for the skin lesions ('pocks') they cause. Smallpox and vaccinia are notable members.

These are naked, icosahedral viruses with double-stranded, linear DNA. They cause pharyngitis, respiratory tract disease, and other infections. They are known for their 40+ antigenic types, some of which cause animal sarcomas.

Naked viruses with an icosahedral capsid, they possess single-stranded, linear, nonsegmented, positive-polarity RNA. They are named for their resemblance to Calicivirus.

A serious respiratory illness caused by the Middle East respiratory syndrome coronavirus (MERS-CoV).

A pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

The period between exposure to the virus and the onset of symptoms.

The most common signs of COVID-19 include fever, tiredness, and a dry cough.

Severe symptoms of COVID-19 can include difficulty breathing, and are more common in older individuals or those with pre-existing health conditions.

The organization that declared COVID-19 a pandemic in March 2020.

The genetic material of the SARS-CoV-2 virus.

The process of creating new virus particles inside a host cell.

RNA viruses are classified into families based on whether they have a lipid membrane (envelope) surrounding their protein coat and the structure of their RNA.

Some viruses, like those in the Poxvirus, Herpesvirus, and Hepadnavirus families, have an outer lipid membrane (envelope) encasing their protein coat.

Viruses belonging to families like Adenovirus, Papovavirus, and Parvovirus lack a lipid membrane (envelope) around their protein coat.

Parvoviruses have single-stranded DNA, while other DNA virus families such as Poxviruses, Herpesviruses, and Hepadnaviruses have double-stranded DNA.

Double-stranded RNA is a feature of Reoviruses, while other RNA virus families such as Picornaviruses, Caliciviruses, Flaviviruses, Togaviruses, Retroviruses, and Coronaviruses have single-stranded RNA.

Reoviruses and Influenza viruses have segmented RNA, meaning their RNA genome is made up of multiple segments.

Picornaviruses, Caliciviruses, Flaviviruses, Togaviruses, Retroviruses, and Coronaviruses have positive-polarity RNA. Other families have negative-polarity RNA.