Virus Structure and Classification (2B) - MCAT Biological and Biochemical Foundations of Living Systems

Group III. Employ virion-encoded polymerases to transcribe mRNA from segmented or non-segmented dsRNA.

Group IV. Genome acts directly as mRNA, enabling rapid translation by host ribosomes upon entry.

Group V. Virion-packaged polymerase transcribes complementary positive-sense RNA for protein synthesis.

Group VI. Reverse transcriptase converts RNA to DNA, allowing integration into the host genome.

Group I. Utilize host transcription machinery to produce mRNA from dsDNA templates, mimicking cellular processes.

Group II. Convert to dsDNA intermediates using host enzymes for subsequent replication and transcription.

$+\text{ssRNA}$ can function directly as mRNA. Permits immediate translation by host machinery, bypassing initial transcription requirements.

Helical symmetry. Capsomeres coil around the genome, forming elongated structures suited for certain RNA viruses.

Icosahedral symmetry. Features 20 equilateral triangular faces, providing efficient spherical enclosure for many viral genomes.

Enveloped viruses have a lipid bilayer; nonenveloped do not. This distinction influences viral stability, transmission routes, and susceptibility to environmental factors.

Viral glycoprotein spikes (peplomers). These structures recognize and bind host receptors, initiating infection through membrane penetration.

Host-derived lipid bilayer surrounding some nucleocapsids. Acquired during viral budding, it enhances stability and facilitates fusion with host membranes.

DNA or RNA. Viruses lack other macromolecules for genomes, relying solely on these nucleic acids for replication and protein coding.

Viral genome plus its surrounding capsid. Forms the core infectious particle, essential for genome protection and delivery into host cells.

Repeating protein subunits that assemble to form the capsid. These identical units self-assemble into symmetrical capsid structures, optimizing viral stability and efficiency.

Protein coat that encloses and protects the viral genome. Composed of protein subunits, it safeguards the genetic material during transmission between host cells.

$-\text{ssRNA}$. Cannot serve as mRNA directly, necessitating polymerase for positive-sense strand synthesis.

Capsid architecture that is neither purely helical nor icosahedral. Seen in viruses like bacteriophages, allowing specialized functions such as tail-mediated injection.

A virus that infects bacteria. Specializes in bacterial hosts, exploiting prokaryotic machinery for replication and lysis.

Head (capsid), tail sheath/tube, base plate, tail fibers. Facilitate precise attachment to bacterial surfaces and efficient genome injection for infection.

Group VII. Involve reverse transcription of pregenomic RNA to DNA during replication cycle.

Specificity of a virus for particular host cells or tissues. Influenced by host factors, it dictates infection patterns and disease manifestations in organisms.

Viral binding to specific host-cell receptors. Receptor interactions ensure selective entry, restricting infection to compatible cell types.