Viral Replication Strategies

Vocabulary flashcards covering the molecular mechanisms of viral replication, including host cell recognition, entry, uncoating, replication strategies according to genome type, and antiviral targets.

Virion

A complete, infectious viral particle consisting of nucleic acid enclosed within a protein coat, capable of existing outside a host cell.

Nucleocapsid

The structural complex consisting of the viral nucleic acid genome enclosed within the protein capsid.

Host Specificity

The selective affinity of a virus for particular host species or cell types, determined by specific interactions between viral attachment proteins ("key") and host cellular receptors ("lock").

Bgp1 Receptor Polymorphism

Genetic variation in the host cell adhesion receptor where BALB/c mice express $Bgp1^a$ allowing strong interaction and infection by Mouse Hepatitis Virus (MHV), whereas SJL/J mice express $Bgp1^b$ showing weak interaction and resistance to infection.

Viral Uncoating

The process of removing the viral protein capsid to expose and release the viral genome into the host cell cytoplasm or nucleus for replication.

Viral Membrane Fusion Model

An entry mechanism specific to enveloped viruses where viral fusion proteins bring the viral envelope into close proximity with the host plasma membrane, merging the lipid bilayers and delivering the nucleocapsid into the cytoplasm.

Hemagglutinin (HA)

An influenza virus envelope glycoprotein that functions as a viral attachment protein by binding to host sialic acid and mediates membrane fusion following a low-pH-induced conformational change in the endosome.

Sialic Acid Linkage Specificity

The structural distinction between host carbohydrate receptors where avian influenza virus preferentially binds sialic acid linked to galactose via an $\alpha 2,3\text{-linkage}$, whereas human influenza virus preferentially binds an $\alpha 2,6\text{-linkage}$.

gp120

The surface glycoprotein of HIV that mediates attachment to host T4 immune cells by binding to the primary CD4 receptor and subsequently interacting with a co-receptor (CCR5 or CXCR4).

gp41

The transmembrane glycoprotein of HIV that exposes a hydrophobic fusion peptide upon co-receptor engagement to facilitate fusion of the viral envelope with the host cell membrane.

Enfuvirtide Mechanism of Action

An antiretroviral fusion inhibitor that binds to HIV gp41 and prevents it from folding, thereby blocking fusion between the viral envelope and host cell membrane.

Bacteriophage Genome Injection

The viral entry mechanism through peptidoglycan cell walls where tail fibers bind host receptors, undergo conformational changes bringing the base plate down, and extend inner core tube proteins to form a lipid bilayer pore that transfers DNA directly into the cytoplasm while leaving the capsid outside.

Poliovirus Receptor (PVR)

The host surface receptor that binds poliovirus, triggering a conformational change that sheds capsid protein VP4 and causes VP1 to insert into the plasma membrane to form a channel for viral RNA entry.

M2 Channel

A proton ion channel in the influenza virus envelope that pumps protons ($H^+$) into the virion core within the acidified endosome, prompting the release of M1 protein from viral ribonucleoproteins (RNPs).

Aggresome Pathway Hijacking

The influenza uncoating process in which viral M1 protein and unanchored ubiquitin chains are recognized by host HDAC6, interacting with dynein and microtubules to promote viral disassembly.

One-Step Virus Growth Curve

A graphical measure of viral replication over time showing a latent phase (intracellular synthesis without cell lysis), a rise phase (virion release by cell lysis), and a plateau determining the burst size.

Burst Size

The average number of infectious viral progeny released from a single infected host cell upon completion of the replication cycle.

RNA-Dependent RNA Polymerase (RdRP)

A viral enzyme required by RNA viruses to transcribe mRNA from RNA templates and replicate RNA genomes, functioning to read and produce RNA without a DNA intermediate.

Positive-Sense ssRNA ($\text{ssRNA (+)}$)

Viral single-stranded RNA oriented $5' \rightarrow 3'$ that functions directly as mRNA and can be immediately translated into viral proteins by host ribosomes.

Negative-Sense ssRNA ($\text{ssRNA (-)}$)

Viral single-stranded RNA oriented $3' \rightarrow 5'$ that is complementary to mRNA and cannot be directly translated by host ribosomes, necessitating the packaging of active RdRP inside the virion.

Reverse Transcriptase (RT)

A viral enzyme encoded by retroviruses that converts a single-stranded RNA genome into double-stranded DNA; it lacks proofreading ability, causing high mutation rates.

Integrase

A retroviral enzyme that facilitates the insertion of viral double-stranded DNA into the host cell chromosome, establishing a provirus.

Provirus

The viral DNA intermediate of a retrovirus that has integrated into the host cell chromosomal DNA, replicating synchronously with the host genome during cell division.

TMPRSS2

A host cell surface transmembrane protease that primes the SARS-CoV-2 spike (S) protein to facilitate viral entry via direct plasma membrane fusion.

Subgenomic mRNA (sg-mRNA)

A nested set of viral mRNAs transcribed by coronaviruses containing a shared $5'$ cap leader sequence and $3'$ poly(A) tail, utilized to translate individual structural and accessory proteins.

Lenacapavir (SUNLENCA)

An antiretroviral medication that binds HIV-1 capsid proteins to disrupt capsid core formation, nuclear transport, and virus assembly and release.