All flashcards
Flashcard 1: What is the pathogenic prion protein isoform called?
Answer: PrPSc. PrPSc denotes the scrapie-associated, misfolded isoform that accumulates and causes prion diseases.
Flashcard 2: Which option correctly distinguishes viroids from viruses by the presence of a capsid?
Answer: Viroids lack a capsid; viruses have a protein capsid. Viroids are naked RNA molecules, whereas viruses package their genomes inside a protein capsid for protection and infectivity.
Flashcard 3: What is the normal cellular prion protein isoform called?
Answer: PrPC. PrPC is the endogenous, properly folded prion protein expressed in healthy cells, particularly in neurons.
Flashcard 4: What is the typical genome form of a viroid?
Answer: Circular single-stranded RNA. Viroid genomes are compact, circular ssRNA structures that enable efficient replication in host cells.
Flashcard 5: Identify the key mechanism by which prions propagate in a host.
Answer: Template-induced misfolding of PrPC into PrPSc. Prions replicate by acting as templates that convert normal PrPC proteins into the pathogenic PrPSc form through direct interaction.
Flashcard 6: What replication strategy is classically associated with viroids?
Answer: Rolling-circle replication. Viroids use a rolling-circle mechanism to generate multimeric RNA intermediates, which are processed into monomeric units.
Flashcard 7: Choose the agent most likely to remain infectious after UV irradiation: prion or viroid?
Answer: Prion. UV irradiation damages nucleic acids, inactivating viroids but not prions, which lack any genome.
Flashcard 8: Which option correctly matches agent to genetic material: prion versus viroid?
Answer: Prion: protein only; viroid: RNA only. Prions transmit via misfolded protein without nucleic acids, while viroids use RNA as their infectious genetic material.
Flashcard 9: Identify the correct statement about the presence of an envelope in prions and viroids.
Answer: Neither prions nor viroids have an envelope. Both agents lack lipid envelopes, consisting only of protein (prions) or RNA (viroids) without additional structures.
Flashcard 10: Which option best describes how viroids cause disease without encoding proteins?
Answer: RNA-mediated disruption of host gene expression (e.g., RNA silencing). Viroid RNA interferes with host RNA processing or triggers silencing pathways, disrupting normal gene expression without protein products.
Flashcard 11: Which host enzyme is most directly used by viroids to replicate their RNA?
Answer: Host RNA polymerase (typically RNA polymerase II). Viroids hijack the host's RNA polymerase II to transcribe their RNA, as they encode no replicative enzymes.
Flashcard 12: Identify the correct statement about viroid protein-coding capacity.
Answer: Viroids do not encode proteins. Viroids lack open reading frames and rely entirely on host machinery, without translating any proteins.
Flashcard 13: What is a prion, in terms of its molecular composition and infectious unit?
Answer: Infectious misfolded protein; no nucleic acid genome. Prions consist solely of misfolded proteins that propagate by inducing conformational changes in normal proteins, without any nucleic acid component.
Flashcard 14: What is a viroid, in terms of its molecular composition and basic structure?
Answer: Small circular single-stranded RNA; no protein coat. Viroids are composed of short, circular ssRNA molecules that infect plants without any protective protein structure.
Flashcard 15: Which option best describes why prions are considered "subviral" agents?
Answer: They lack nucleic acids yet can transmit disease. Prions are subviral because they transmit infectivity through protein alone, defying the need for nucleic acids in replication.
Flashcard 16: Which option best describes why viroids are considered "subviral" agents?
Answer: They are naked RNA without a capsid or envelope. Viroids are subviral as they consist only of RNA, lacking the protein capsid that encapsulates viral genomes.
Flashcard 17: What conformational change is most associated with conversion of PrPC to PrPSc?
Answer: Increase in eta-pleated sheet content. The pathogenic PrPSc form has higher eta-sheet structure, making it insoluble and aggregation-prone compared to the alpha-helical PrPC.
Flashcard 18: What type of host immune response is typically elicited by prion infections?
Answer: Minimal or absent adaptive immune response. Prions, being self-proteins, evade strong adaptive immunity, leading to little inflammation or antibody production.
Flashcard 19: Which tissue is primarily affected in prion diseases?
Answer: Central nervous system. Prion diseases primarily target the brain, where PrPSc accumulation causes neuronal damage and spongiform changes.
Flashcard 20: What characteristic neuropathology is classically seen in prion diseases?
Answer: Spongiform encephalopathy (vacuolization of brain tissue). Prion-induced misfolding leads to vacuole formation in neurons, creating a sponge-like appearance in brain tissue.
Flashcard 21: What is the typical clinical course of prion diseases once symptomatic?
Answer: Progressive neurodegeneration leading to death. Prion diseases are relentlessly progressive, with accumulating PrPSc causing irreversible neuronal loss and fatal outcomes.
Flashcard 22: Which option best describes the resistance of prions to standard sterilization methods?
Answer: Highly resistant to heat, radiation, and proteases. The stable eta-sheet structure of PrPSc confers resistance to denaturation by physical and chemical agents.
Flashcard 23: Identify the correct statement about prion replication compared with viral replication.
Answer: No genome replication; propagation occurs by protein conformational conversion. Unlike viruses that replicate genomes, prions propagate solely by inducing host protein misfolding without nucleic acid involvement.
Flashcard 24: Which option correctly distinguishes prions from viroids by the presence of nucleic acid?
Answer: Prions: none; viroids: RNA genome only. Prions lack any nucleic acid, relying on protein for infectivity, while viroids use RNA as their sole genetic material.
Flashcard 25: What type of organisms are classically infected by viroids?
Answer: Plants. Viroids primarily infect plant hosts, where they replicate and cause diseases like potato spindle tuber disease.