Virology Chapter on Orthomyxoviridae

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Questions and Answers

What role does the low pH within the endosome play in virus-mediated membrane fusion?

It causes a conformational change in HA that facilitates membrane fusion. (correct)

It degrades viral nucleocapsids.

It enhances glycoprotein assembly.

It promotes RNA synthesis.

Which statement best describes the process of genetic reassortment in influenza viruses?

It occurs exclusively in single-infected cells.

It requires the presence of amino acid mutations.

It is caused by viral polymerase errors during replication.

It results from intermingling of genome segments in coinfected cells. (correct)

What is the primary function of the M2 ion channel protein in the viral life cycle?

To assist in mRNA synthesis.

To facilitate the entry of ions that trigger conformational changes in the virus. (correct)

To anchor the nucleocapsid to the cell surface.

To degrade cellular RNA.

What role does hemagglutinin (HA) play during the process of viral maturation?

It is cleaved into functional parts before budding. Signup and view all the answers

What distinguishes the transcription mechanisms of orthomyxoviruses from other RNA viruses?

They integrate more closely with cellular processes for transcription. Signup and view all the answers

What is the arrangement of the HA spike on the influenza virus particle?

A trimer of intertwined HA1 and HA2 dimers Signup and view all the answers

Which statement describes the function of HA in the influenza virus?

It aids in the entry of the virus by fusing with host cell membranes Signup and view all the answers

What is the role of neuraminidase in the influenza virus?

It facilitates the release of new viral particles from infected cells Signup and view all the answers

What is located at the top of each large globule of the virus particle?

Binding site Signup and view all the answers

Why is the cleavage that separates HA1 and HA2 necessary?

To enable the virus to be infectious Signup and view all the answers

How does low pH influence the HA molecule in the influenza virus?

It activates the fusion activity of HA Signup and view all the answers

Why are the five antigenic sites on the HA molecule significant?

They are key for neutralizing the virus and exhibit extensive mutations Signup and view all the answers

What is the primary function of the neuraminidase (NA) enzyme in the influenza virus?

To remove sialic acid from glycoproteins Signup and view all the answers

What structural component of the virus is described as a tetramer composed of four identical monomers?

Hemagglutinin (HA) Signup and view all the answers

What structural component contributes to the stability of the HA spike?

The trimerization of HA1 and HA2 dimers Signup and view all the answers

What is indicated by the molecular weights of the glycoproteins HA and NA?

The weights appear larger due to carbohydrate addition Signup and view all the answers

What is the role of the catalytic site found on the NA spike?

To cleave sialic acid from host cells Signup and view all the answers

How are RNA segments in influenza virus categorized?

In order of decreasing size Signup and view all the answers

What feature of neuraminidase allows it to function in the viral life cycle?

Its active sites for sialic acid removal Signup and view all the answers

What typically happens to HA in more virulent influenza viruses?

It adapts to utilize a broader range of host enzymes Signup and view all the answers

What type of enzyme is neuraminidase classified as?

Sialidase Signup and view all the answers

What is a key characteristic of the NA spikes on influenza viruses?

They exist in a tetrameric structure. Signup and view all the answers

The hydrophobic membrane domain of the viral proteins is primarily involved in which function?

Facilitating membrane fusion Signup and view all the answers

Influenza viruses are typically restricted to which part of the body due to protease activity?

Respiratory tract Signup and view all the answers

What is the role of the cleavage of HA into HA1 and HA2?

It is necessary for the virus to be infectious. Signup and view all the answers

What anchors the HA and NA proteins in the viral membrane?

Hydrophobic amino acids located at their carboxyl and amino terminals. Signup and view all the answers

Which sites on HA are significant for antigenic variation?

Five major antigenic sites labeled A–E. Signup and view all the answers

What function does neuraminidase (NA) serve during the virus life cycle?

It prevents the self-aggregation of virions. Signup and view all the answers

What characteristic allows the HA2 to provide fusion activity?

Its amino terminal region, which contains fusion peptide. Signup and view all the answers

How does NA contribute to the release of virus particles?

By removing sialic acid from viral glycoproteins. Signup and view all the answers

What happens to the fusion peptide in HA during low pH conditions?

It is exposed due to a conformational change. Signup and view all the answers

Which part of the NA molecule corresponds to its active site?

The upper surface of the molecule. Signup and view all the answers

What is the significance of antigenic drift and shift in influenza viruses?

They provide the virus with selective advantages in the presence of antibodies. Signup and view all the answers

What role does the carboxyl terminal play for HA and NA proteins?

It protrudes through the membrane. Signup and view all the answers

What is the primary role of neuraminidase (NA) in the influenza virus lifecycle?

To remove terminal sialic acids from glycoproteins Signup and view all the answers

How many genome segments yield monocistronic mRNAs in the influenza virus?

Six Signup and view all the answers

What is the function of the NS1 protein in the influenza virus?

Binding to poly(A) sequences and inhibiting splicing Signup and view all the answers

Which protein is involved in the nuclear export of viral RNPs?

NS2 protein Signup and view all the answers

What happens to virus particles that fail to encapsidate the complete set of genome segments?

They are considered noninfectious Signup and view all the answers

What is the function of hemagglutinin (HA) in the influenza virus?

To facilitate viral entry into host cells Signup and view all the answers

Which type of RNA segments undergo splicing to yield two mRNAs?

Two of the genome segments Signup and view all the answers

What type of mRNA is produced from the six genome segments that are translated into viral proteins?

Monocistronic mRNA Signup and view all the answers

How does α-amanitin affect influenza virus replication?

It blocks cellular transcription Signup and view all the answers

What is the outcome of having a large RNA segment missing in some virus particles?

They can still agglutinate but are noninfectious Signup and view all the answers

Study Notes

Influenza Virus Structural Components

RNA segments numbered by decreasing size.
Two glycoproteins, Hemagglutinin (HA) and Neuraminidase (NA), have molecular weights of approximately 76,000 and 56,000 due to carbohydrate addition.
Hemagglutinin (HA) is composed of HA1 and HA2 dimers forming a stalk capped by a large globule.
Five antigenic sites on HA exhibit extensive mutations, playing a role in viral neutralization.
The amino terminal of HA2, formed by cleavage, is crucial for viral envelope fusion with cell membranes.
Low pH induces a conformational change in HA, activating its fusion activity.
HA spikes consist of three HA1 and HA2 dimers, providing enhanced stability compared to monomers.
Neuraminidase (NA) operates through a tetramer structure with four active catalytic sites, facilitating the release of virus particles from infected cells by removing sialic acid.

Viral Mechanisms and Assembly

Cleavage of HA into HA1 and HA2 by cellular proteases is essential for viral infectivity.
Influenza viruses typically remain local to the respiratory tract due to specific protease enzymes present in that region.
Viral transcription occurs in the nucleus, utilizing cellular machinery, which differs from other RNA viruses.
Eight genome segments yield monocistronic mRNAs converting into six viral proteins; two undergo splicing for additional mRNAs.
The NS1 protein regulates gene expression by binding to poly(A) sequences, inhibiting pre-mRNA splicing, and blocking nuclear export of spliced mRNAs.

Antigenic Variability

Influenza viruses experience frequent changes in HA and NA, resulting in antigenic drift and shift.
Antigenic variants possess selective advantages, enabling the virus to evade the immune response.

Virus Replication and Egress

Maturation occurs through budding from the cell surface, involving the assembly of components in the nucleus and cytoplasm.
Glycoproteins, HA and NA, undergo synthesis and modifications in the endoplasmic reticulum before being inserted into the plasma membrane.
The M2 ion channel facilitates the entry of ions, triggering the release of viral RNPs upon endosomal fusion.
Viral nucleocapsids are released into the cytoplasm after conformational changes in HA induced by low pH conditions.
Genetic reassortment occurs in co-infected cells, leading to significant variations in influenza virus strains, with documented rates of reassortment up to 40%.

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Description

Explore the intricate details of Orthomyxoviridae, focusing on RNA segments and glycoproteins such as HA and NA. This quiz provides insights into the molecular weights and structural complexities of these viruses. Test your knowledge on this key area of virology and understand their replication processes.