Biology: Viruses and Viroids

Viruses:
- Composed of genetic material (DNA or RNA) surrounded by a protein coat (capsid)
- May have a lipid envelope (derived from host cell membrane)
- Size: 20-400 nm in diameter
- Function: replicate and express genetic material within host cells
Viroids:
- Small, single-stranded RNA molecules (250-400 nucleotides)
- Infect plants and cause disease
- No protein coat or lipid envelope
- Function: replicate and express genetic material within host cells
Prions:
- Infectious proteins that cause disease in animals
- Composed of abnormally folded protein (PrP) that can induce normal protein to fold abnormally
- No genetic material (DNA or RNA)
- Function: cause misfolding of normal protein, leading to cell death and tissue damage

Viruses:
- Attach to host cell surface receptors
- Penetrate host cell membrane (endocytosis or fusion)
- Release genetic material into host cell cytoplasm
- Transcribe and translate genetic material into viral proteins
- Assemble new viral particles
- Release new viral particles from host cell (lysis or budding)
Viroids:
- Replicate within host cell nucleus or cytoplasm
- Use host cell enzymes to replicate and transcribe genetic material
- Produce new viroid particles
Prions:
- Infectious prion protein (PrP) binds to normal prion protein (PrPc)
- Induces misfolding of PrPc into PrP
- Misfolded PrP accumulates and causes cell death and tissue damage

Viruses:
- Infect various hosts, including animals, plants, and bacteria
- Transmission: direct contact, airborne, or vector-borne (insects, ticks, etc.)
Viroids:
- Infect plants
- Transmission: mechanical contact, contaminated water, or infected pollen
Prions:
- Infect animals, including humans
- Transmission: direct contact, contaminated food, or infected tissue transplants

Viruses:
- Evolve through mutation and genetic recombination
- Classified based on genome type (DNA or RNA), capsid structure, and host range
- Divided into 7 orders: Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, Picornavirales, Retrovirales, and Tymovirales
Viroids:
- Evolve through mutation and genetic recombination
- Classified based on genome structure and host range
- Divided into 2 families: Avsunviroidae and Pospiviroidae
Prions:
- Evolve through conformational changes in protein structure
- Classified based on protein structure and host range
- No formal classification system, but divided into several subgroups based on protein structure and disease association

Viruses:
- Cause a wide range of diseases, including common cold, influenza, HIV, and Ebola
- Symptoms: fever, fatigue, respiratory distress, skin lesions, and more
Viroids:
- Cause diseases in plants, including stunted growth, yellowing, and necrosis
- Symptoms: vary depending on the specific viroid and host plant
Prions:
- Cause diseases in animals, including mad cow disease, scrapie, and Creutzfeldt-Jakob disease
- Symptoms: neurological disorders, including memory loss, confusion, and loss of coordination

Viruses consist of genetic material (DNA or RNA) surrounded by a protein coat (capsid) and may have a lipid envelope derived from the host cell membrane.
Viruses range in size from 20-400 nm in diameter and function to replicate and express genetic material within host cells.
Viroids are small, single-stranded RNA molecules (250-400 nucleotides) that infect plants and cause disease, lacking a protein coat or lipid envelope.
Prions are infectious proteins that cause disease in animals, composed of abnormally folded protein (PrP) that can induce normal protein to fold abnormally, with no genetic material (DNA or RNA).

Viruses replicate by attaching to host cell surface receptors, penetrating the host cell membrane, releasing genetic material into the host cell cytoplasm, transcribing and translating genetic material into viral proteins, assembling new viral particles, and releasing new viral particles from the host cell.
Viroids replicate within the host cell nucleus or cytoplasm using host cell enzymes to replicate and transcribe genetic material, producing new viroid particles.
Prions replicate by infectious prion protein (PrP) binding to normal prion protein (PrPc), inducing misfolding of PrPc into PrP, and accumulating misfolded PrP, causing cell death and tissue damage.

Viruses infect various hosts, including animals, plants, and bacteria, and can be transmitted through direct contact, airborne, or vector-borne means.
Viroids infect plants and can be transmitted through mechanical contact, contaminated water, or infected pollen.
Prions infect animals, including humans, and can be transmitted through direct contact, contaminated food, or infected tissue transplants.

Viruses evolve through mutation and genetic recombination and are classified based on genome type (DNA or RNA), capsid structure, and host range, with 7 orders: Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, Picornavirales, Retrovirales, and Tymovirales.
Viroids evolve through mutation and genetic recombination and are classified based on genome structure and host range, with 2 families: Avsunviroidae and Pospiviroidae.
Prions evolve through conformational changes in protein structure and are classified based on protein structure and host range, with no formal classification system, but divided into several subgroups based on protein structure and disease association.

Viruses cause a wide range of diseases, including common cold, influenza, HIV, and Ebola, with symptoms including fever, fatigue, respiratory distress, skin lesions, and more.
Viroids cause diseases in plants, including stunted growth, yellowing, and necrosis, with symptoms varying depending on the specific viroid and host plant.
Prions cause diseases in animals, including mad cow disease, scrapie, and Creutzfeldt-Jakob disease, with symptoms including neurological disorders, such as memory loss, confusion, and loss of coordination.