Influenza Virus Mechanisms and Assays

This set of flashcards covers key vocabulary terms and concepts related to the mechanisms of influenza virus infection and assays used to detect it.

Hemagglutinin

A viral protein that allows influenza virus to bind to sialic acid on red blood cells.

Sialic Acid

A terminal sugar linked to receptor proteins on red blood cells that influenza hemagglutinin binds to.

Immunological Assay

A test to measure the presence of specific antibodies in a patient, indicating recent infection.

Hemagglutination Inhibition Test

A clinical test to determine if antibodies against hemagglutinin are present in a patient's serum.

Receptor Mediated Endocytosis

A process by which cells internalize the influenza virus after it binds to its receptor.

Acidification of Endosomes

A defense mechanism used by host cells that influences the structural changes in the hemagglutinin protein, allowing viral entry.

Amantadine

An antiviral drug that inhibits the M2 protein of influenza, preventing proton access and viral fusion with endosomes.

Oseltamivir (Tamiflu)

An antiviral that inhibits neuraminidase, preventing the release of new influenza viruses from infected cells.

Cap Snatching

A strategy used by influenza virus to inhibit host protein synthesis by cleaving caps from host mRNA.

Programmed Ribosomal Frameshifting

A mechanism allowing influenza virus to produce different proteins from its RNA by shifting the reading frame during translation.

Neuraminidase

An enzyme of the influenza virus that cleaves sialic acid to enable the release of viral particles from infected cells.

Matrix Protein 2 (M2)

A viral envelope protein that forms a proton channel, facilitating acidification and viral fusion.

Polyadenylation

The addition of a poly A tail to mRNA, important for stability and translation of the viral RNA.

Viral Ribonucleoproteins

Complexes containing RNA segments of the influenza virus that are trafficked to the host nucleus for replication.

Molecular Serum

The fluid that remains after blood clotting used to separate components for immunological assays.

Fusion Peptide

A domain of the hemagglutinin protein that facilitates the fusion of the viral envelope with the endosomal membrane.

Endosome

A membrane-bound compartment that contains the internalized influenza virus post-entry.

RNA-dependent RNA polymerase (RdRP)

An enzyme necessary for the replication of the influenza virus's RNA genome.

Trimer

A complex formed by three identical subunits of hemagglutinin involved in receptor binding.

Alternative Splicing

A process that allows multiple protein variants to be produced from a single mRNA transcript.

Nonstructural Proteins

Proteins expressed by the virus that are not part of the viral structure but play roles in viral replication.

Endosomal Acidification

The process of lowering the pH in endosomes, crucial for the activation and functioning of viral proteins.

Cytoplasm

The gel-like substance inside cells where various cellular processes occur and viral replication takes place.

Hemagglutinin

A viral protein that allows influenza virus to bind to sialic acid on red blood cells.

Sialic Acid

A terminal sugar linked to receptor proteins on red blood cells that influenza hemagglutinin binds to.

Immunological Assay

A test to measure the presence of specific antibodies in a patient, indicating recent infection.

Hemagglutination Inhibition Test

A clinical test to determine if antibodies against hemagglutinin are present in a patient's serum.

Receptor Mediated Endocytosis

A process by which cells internalize the influenza virus after it binds to its receptor.

Acidification of Endosomes

A defense mechanism used by host cells that influences the structural changes in the hemagglutinin protein, allowing viral entry.

Amantadine

An antiviral drug that inhibits the M2 protein of influenza, preventing proton access and viral fusion with endosomes.

Oseltamivir (Tamiflu)

An antiviral that inhibits neuraminidase, preventing the release of new influenza viruses from infected cells.

Cap Snatching

A strategy used by influenza virus to inhibit host protein synthesis by cleaving caps from host mRNA.

Programmed Ribosomal Frameshifting

A mechanism allowing influenza virus to produce different proteins from its RNA by shifting the reading frame during translation.

Neuraminidase

An enzyme of the influenza virus that cleaves sialic acid to enable the release of viral particles from infected cells.

Matrix Protein 2 (M2)

A viral envelope protein that forms a proton channel, facilitating acidification and viral fusion.

Polyadenylation

The addition of a poly A tail to mRNA, important for stability and translation of the viral RNA.

Viral Ribonucleoproteins

Complexes containing RNA segments of the influenza virus that are trafficked to the host nucleus for replication.

Molecular Serum

The fluid that remains after blood clotting used to separate components for immunological assays.

Fusion Peptide

A domain of the hemagglutinin protein that facilitates the fusion of the viral envelope with the endosomal membrane.

Endosome

A membrane-bound compartment that contains the internalized influenza virus post-entry.

RNA-dependent RNA polymerase (RdRP)

An enzyme necessary for the replication of the influenza virus's RNA genome.

Trimer

A complex formed by three identical subunits of hemagglutinin involved in receptor binding.

Alternative Splicing

A process that allows multiple protein variants to be produced from a single mRNA transcript.

Nonstructural Proteins

Proteins expressed by the virus that are not part of the viral structure but play roles in viral replication.

Endosomal Acidification

The process of lowering the pH in endosomes, crucial for the activation and functioning of viral proteins.

Cytoplasm

The gel-like substance inside cells where various cellular processes occur and viral replication takes place.

Steps of Influenza Virus Entry

1. Binding: Hemagglutinin on the viral surface binds to sialic acid receptors on the host cell membrane. 2. Internalization: The virus is taken into the host cell via receptor-mediated endocytosis, forming an endosome. 3. Acidification: The M2 proton channel in the viral envelope allows protons from the endosome to enter the virion, acidifying its interior. 4. Conformational Change: The acidic environment causes hemagglutinin to undergo a conformational change, exposing its fusion peptide. 5. Membrane Fusion: The fusion peptide inserts into the endosomal membrane, facilitating the fusion of the viral envelope with the endosomal membrane. 6. Release: Viral ribonucleoproteins (vRNPs) and other viral components are released into the host cell cytoplasm.

Steps of Cap Snatching

1. Host mRNA Recognition: The viral RNA polymerase complex, associated with vRNPs, binds to capped host mRNAs in the nucleus. 2. Cap Cleavage: The viral endonuclease component of the polymerase complex cleaves the 5' cap and a short oligonucleotide (about 10-18 nucleotides) from the host mRNA. 3. Primer Utilization: This snatched capped RNA fragment serves as a primer for viral mRNA synthesis. 4. Viral Transcription: The viral RNA-dependent RNA polymerase uses this primer to begin transcribing negative-sense viral RNA (vRNA) into positive-sense viral mRNA. 5. Host Protein Synthesis Inhibition: By cleaving the caps, the virus effectively deprives host mRNAs of the necessary component for their translation, thereby inhibiting host gene expression.

Steps of Influenza Virus Release

1. Assembly: Newly synthesized viral components (vRNPs, matrix proteins, envelope proteins like HA and NA) assemble at the host cell membrane. 2. Budding: New virions bud off from the host cell surface, enclosing vRNPs and acquiring an envelope derived from the host membrane. 3. Sialic Acid Cleavage: Neuraminidase (NA) on the surface of the newly formed virions cleaves sialic acid residues on both the host cell surface and the viral envelope. 4. Prevention of Aggregation: This cleavage prevents the newly released virions from re-attaching to the infected cell or aggregating with each other, allowing them to spread and infect other cells.