Subviral Particles and Nonliving Infectious Agents

Questions and Answers

What is the primary difference between viruses and subviral particles?

Subviral particles have a lipid envelope while viruses do not

Viruses can reproduce on their own while subviral particles cannot

Subviral particles are smaller than viruses (correct)

Viruses are living while subviral particles are nonliving

What are the two main types of subviral particles?

Prions and chromosomes

Viroids and lipids

Proteins and RNA

Viroids and prions (correct)

What is unique about the RNA of viroids?

It is made of DNA

It is double-stranded

It is always found in humans

It is single-stranded and circular (correct)

Why are viroids thought to be catalytic?

Because they can make or break covalent bonds Signup and view all the answers

What is a characteristic that viruses and subviral particles share?

They are both acellular Signup and view all the answers

Why do viruses and subviral particles need a host?

Because they lack organelles and cannot make their own energy Signup and view all the answers

What was a previous limitation in the discovery of viroids?

They were only found in plants Signup and view all the answers

What is a recent development in the discovery of viroids?

They have been found to infect humans Signup and view all the answers

What is the main difference between viroids and virions?

Viroids are only genetic material, while virions have a protein coat and genetic material. Signup and view all the answers

What makes prions different from viruses and viroids?

Prions are made up of only proteins, with no genetic material. Signup and view all the answers

What is the normal conformation of a protein?

Alpha-helix Signup and view all the answers

What happens when a prion protein comes into contact with a normal protein?

The normal protein's conformation changes to a beta-sheet. Signup and view all the answers

What is the result of protein deposits forming in the brain?

The protein deposits cause disease when they are removed, leaving holes in the brain. Signup and view all the answers

What is the name of the protein that makes up a prion?

PrP Signup and view all the answers

What is thought to be the mechanism by which prions cause infection?

The prion protein's beta-sheet conformation causes the normal protein to change its shape. Signup and view all the answers

Why are scientists still uncertain about prions?

Because prions have only recently been discovered. Signup and view all the answers

Study Notes

Subviral Particles

Subviral particles are smaller than viruses and are categorized as nonliving infectious agents.
Nonliving infectious agents include viruses and subviral particles, which are acellular, meaning they're only made of a protein coat, or a capsid, that protects genetic information (DNA or RNA).

Characteristics of Viruses

Viruses require a host to make their own energy (ATP) and reproduce.
They can't divide or reproduce on their own due to their small size and lack of organelles.

Subviral Particles: Viroids

Viroids are smaller than viruses, composed of a single strand of circular RNA.
Until recently, viroids were only found to infect plants, but now they've been found in humans, specifically in the case of Hepatitis D.
Viroids can self-cleave to create more viroids due to their catalytic RNA, which can make or break covalent bonds.
Note: Viroids are different from virions, which are whole viruses consisting of a protein coat plus RNA or an envelope.

Subviral Particles: Prions

Prions are proteinaceous infectious particles, composed only of proteins with no genetic material (RNA or DNA).
Prions have a different conformation than normal proteins, with a beta-sheet structure instead of an alpha-helix.
When a prion protein (PrP) comes into contact with a normal protein, it can change the normal protein's conformation, leading to protein deposits.
These protein deposits can cause disease, especially in the brain, where cleanup of the deposits can leave holes in the brain tissue.