Viruses and Viroids

The transcript discusses the discovery and characteristics of viruses, focusing on the tobacco mosaic virus (TMV) as the first recognized virus. It explains the nature of viruses as non-living entities that require a host for replication, their genetic material, and the diseases they cause in humans and plants. The structure of TMV and bacteriophages is detailed, along with the introduction of viroids and prions as simpler infectious agents.

What was the significant finding of Martinus Willem Beijerinck regarding the tobacco mosaic virus?

• It was larger than any known bacterium.

• It remained infectious even after dilution.

• It could reproduce independently.

• It could be crystallized like a chemical substance.

Why are viruses considered to be at the boundary between living and non-living things?

• They can be crystallized and lack cellular structure.

• They possess both RNA and DNA.

• They can reproduce outside a host cell.

• They have a cellular structure.

Which type of genetic material is found in the tobacco mosaic virus?

• Single-stranded RNA

• Double-stranded DNA

• Double-stranded RNA

• Single-stranded DNA

What is a common characteristic of viruses that infect plants?

• They have both RNA and DNA.

• They have single-stranded RNA.

• They have double-stranded DNA.

• They have a cellular structure.

What is the primary structural component of the tobacco mosaic virus?

• A polyhedral head and a tail

• A protein capsid with capsomeres

• A double-stranded DNA core

• A lipid envelope

What distinguishes viroids from viruses?

• Viroids contain double-stranded DNA.

• Viroids lack a protein coat.

• Viroids are larger than viruses.

• Viroids have a protein coat.

What is a unique feature of prions compared to other infectious agents?

• They contain nucleic acids.

• They are composed mainly of proteins.

• They can be easily destroyed.

• They cause diseases in plants.