MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 2b Virus Structure Classification

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This deck focuses on 2b Virus Structure Classification, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is the Baltimore classification system based on?

Answer: Genome type and the pathway used to generate mRNA. Organizes viruses into groups reflecting nucleic acid nature and mRNA synthesis mechanisms.

Flashcard 2: Which Baltimore group is double-stranded RNA (dsRNA) viruses?

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

Flashcard 3: Which Baltimore group is positive-sense single-stranded RNA ($+\text{ssRNA}$) viruses?

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

Flashcard 4: Which Baltimore group is negative-sense single-stranded RNA ($-\text{ssRNA}$) viruses?

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

Flashcard 5: Which Baltimore group is single-stranded RNA reverse-transcribing viruses (retroviruses)?

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

Flashcard 6: Which Baltimore group is double-stranded DNA (dsDNA) viruses?

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

Flashcard 7: Which Baltimore group is single-stranded DNA (ssDNA) viruses?

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

Flashcard 8: Identify the mRNA equivalence of a $+\text{ssRNA}$ viral genome upon entry.

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

Flashcard 9: Which capsid symmetry is characterized by a rod-like or filamentous appearance?

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

Flashcard 10: Which capsid symmetry is characterized by a roughly spherical appearance?

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

Flashcard 11: What is the key structural difference between enveloped and nonenveloped viruses?

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

Flashcard 12: Which viral surface proteins mediate host-cell attachment and entry?

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

Flashcard 13: What is a viral envelope?

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

Flashcard 14: Which two macromolecule types can serve as a viral genome?

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

Flashcard 15: What is the viral nucleocapsid?

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

Flashcard 16: What are capsomeres in viral structure?

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

Flashcard 17: What is the capsid of a virus?

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

Flashcard 18: Which genome type must carry an RNA-dependent RNA polymerase in the virion to make mRNA after entry?

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

Flashcard 19: What is a complex virus capsid morphology?

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

Flashcard 20: What is a bacteriophage?

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

Flashcard 21: Identify the typical bacteriophage structures used for attachment and genome delivery.

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

Flashcard 22: Which Baltimore group is double-stranded DNA reverse-transcribing viruses (pararetroviruses)?

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

Flashcard 23: What is viral tropism?

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

Flashcard 24: Which property primarily determines viral tropism at the entry step?

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