Prions and Viroids

Prions and viroids stretch students’ understanding of infectious disease because they defy the typical models of viruses and bacteria. Active learning helps students confront these exceptions directly, making abstract concepts like protein misfolding and naked RNA more concrete through discussion, mapping, and case analysis.

• 11th Grade
• Biology
• 3 activities
• 30 min–40 min

Learning Objectives

1. Compare the structural composition of viruses, prions, and viroids, identifying key differences in genetic material and protein structure.
2. Explain the mechanism by which a misfolded prion protein induces conformational changes in normal prion proteins.
3. Analyze the challenges associated with developing treatments or cures for prion and viroid diseases due to their unique infectious agents.
4. Classify specific diseases, such as Creutzfeldt-Jakob disease and potato spindle tuber disease, as being caused by prions or viroids, respectively.

Socratic Seminar

⏱ 40 min·Whole Class

Socratic Seminar: Can a Protein Cause Disease?

Students read a one-page excerpt on prion biology before class, then engage in a facilitated whole-class discussion. The central prompt is: 'If prions have no DNA or RNA, how do they replicate?' Students must use evidence from the reading and prior knowledge to reason through this question together.

Prepare & details

Differentiate between viruses, prions, and viroids based on their composition and mode of infection.

Facilitation Tip: During the Socratic Seminar, pause after each student comment to ask another student to paraphrase or extend the idea, keeping the conversation grounded in evidence from the readings.

Setup: Chairs arranged in two concentric circles

Materials: Discussion question/prompt (projected), Observation rubric for outer circle

• Analyze
• Evaluate
• Create
• Social Awareness
• Relationship Skills

Concept Mapping

⏱ 30 min·Individual

Concept Mapping: Comparing Infectious Agents

Students individually create a concept map connecting viruses, prions, and viroids based on their composition, mode of infection, and target host. They share maps with a partner to identify areas of disagreement, then revise and justify their final version.

Prepare & details

Explain how prions can cause neurodegenerative diseases without genetic material.

Facilitation Tip: For the Concept Mapping activity, provide colored pencils or digital tools so students can visually separate structure, disease type, and treatment challenges for each agent.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Case Study Analysis

⏱ 35 min·Small Groups

Case Study Analysis: The BSE Outbreak

Small groups analyze a brief case study on the 1980s-90s BSE crisis in the UK, tracing the epidemiology of prion spread. Groups answer analytical questions about why the disease was so difficult to detect, treat, and contain, and identify the specific biological properties of prions that made containment hard.

Prepare & details

Analyze the challenges in treating diseases caused by prions and viroids.

Facilitation Tip: In the Case Study on BSE, assign roles such as epidemiologist, farmer, and public health official to ensure multiple perspectives are represented in the analysis.

Setup: Groups at tables with case materials

Materials: Case study packet (3-5 pages), Analysis framework worksheet, Presentation template

• Analyze
• Evaluate
• Create
• Decision-Making
• Self-Management

Teaching This Topic

Teaching prions and viroids works best when you emphasize the ‘what’s missing’ approach. Highlight that prions lack nucleic acid entirely and viroids lack protein coats, which explains why immune systems and medicines struggle to target them. Avoid overcomplicating with protein biochemistry; focus instead on the functional consequences of missing components. Research shows students grasp these concepts more easily when they compare agents side-by-side rather than studying them in isolation.

What to Expect

By the end of these activities, students will confidently distinguish prions, viroids, and viruses based on structure and mechanism, explain why standard treatments fail against them, and apply this knowledge to real-world outbreaks like BSE. Success looks like clear articulation of misfolding chains, precise classification of agents, and thoughtful discussion of treatment barriers.

Watch Out for These Misconceptions

Common Misconception

During Concept Mapping: Comparing Infectious Agents, watch for students who incorrectly group prions with viruses because both cause disease. Redirect by having them compare the composition column first: viruses have DNA/RNA and protein, prions have protein only.

What to Teach Instead

Use the concept map’s structure column to guide students to note that prions contain no nucleic acid, while viruses always include genetic material. Ask them to highlight this difference in a different color on their maps.

Common Misconception

During the Case Study: The BSE Outbreak, listen for students who assume prion diseases can be cured like bacterial infections. Redirect by having them review the case’s timeline and treatment section to identify why medications failed.

What to Teach Instead

Ask students to annotate the case study with evidence about treatment attempts, then discuss as a class why the absence of a genome or metabolic activity makes prions untreatable with standard drugs.

Assessment Ideas

Discussion Prompt

After the Socratic Seminar: Can a Protein Cause Disease?, use students’ final arguments to assess their understanding of protein misfolding and infectiousness. Look for references to conformational change and chain reactions, and note which students cite evidence from the readings or prior knowledge accurately.

Quick Check

During Concept Mapping: Comparing Infectious Agents, collect the maps and assess accuracy by checking if students correctly matched characteristics like ‘misfolded protein’ to prions and ‘affects nervous system’ to both prions and some viruses. Review common errors as a class to clarify misunderstandings.

Exit Ticket

After the Case Study: The BSE Outbreak, collect exit tickets where students write one challenge in treating prion diseases and one in preventing viroid diseases in agriculture. Assess for specificity, such as mentioning the lack of genetic material in prions or the absence of a protein coat in viroids as reasons for the challenges.

Extensions & Scaffolding

• Challenge early finishers to research and present on a lesser-known prion disease (e.g., fatal familial insomnia) or viroid disease (e.g., coconut cadang-cadang) and connect it to agricultural or public health policy.
• For students who struggle, provide sentence stems for the Socratic Seminar (e.g., 'Prions spread because...') and pre-labeled concept map branches to match key terms.
• Deeper exploration: Invite students to design a public health campaign poster targeting prevention of prion diseases in livestock or viroid spread in crops, including scientific justifications for their strategies.

Key Vocabulary

Prion	An infectious agent composed of misfolded proteins that can induce normal proteins to misfold, leading to disease. Prions lack genetic material.
Viroid	A small, circular, naked RNA molecule that is infectious and can cause plant diseases by interfering with gene expression. It lacks protein coats.
Misfolded protein	A protein whose three-dimensional shape is not correct, which can lead to loss of function or the ability to induce misfolding in other proteins, as seen in prions.
Neurodegenerative disease	A disease characterized by the progressive loss of structure or function of neurons, often leading to death. Prion diseases are a type of neurodegenerative disease.