Acellular viruses and prions

Acellular Viruses

General Characteristics:

Acellular viruses are non-living entities made of genetic material (either DNA or RNA) enclosed in a protein coat termed a capsid.
They are incredibly small, often measured in nanometers, and not considered organisms as they lack cellular structure.
Viruses do not perform metabolic activities, therefore, they require a host cell to reproduce, replicate their genetic material, and produce viral proteins.

Classification of Acellular Viruses:

Acellular viruses can be classified based on several factors such as the type of nucleic acid (DNA or RNA), replication strategies, and the structure of their capsids.
Some common types of DNA viruses include adenoviruses, herpesviruses, and papillomaviruses.
Representative RNA viruses include influenza virus, HIV, and coronaviruses.

Viral Reproduction:

Viral reproduction, known as the viral life cycle, involves infecting a host cell, taking control of it, replicating the genome, and producing new viral particles that get released.
The spread of viruses in humans often causes diseases, as the host cell’s normal function is disrupted, and immune responses can cause damage.

Role in the Ecosystem:

Viruses, through infection and subsequent diseases, can impact population dynamics in nature.
Some studies suggest that viruses can play a role in the evolution of their host species through viral-host coevolution.

Prions

General Characteristics:

Prions are infectious proteins devoid of nucleic acid, and they cause diseases by inducing normal proteins in the host organism to undergo a conformational change.
Prion proteins are resistant to denaturation, making them hard to destroy, and can cause fatal diseases in both humans and animals such as Creutzfeldt-Jakob disease and mad cow disease.

Classification of Prions:

Prions do not have diversity or subclasses like other microorganisms due to their simple structure.
However, they can cause a range of different diseases, each associated with a different misfolded protein.

Prion Propagation:

Prion propagation occurs through the misfolding of normal proteins in the host organism into a prion configuration, creating a chain reaction of misfolding.
This propagation often leads to the slow progression of degenerative neural diseases.

Role in the Ecosystem:

Prions affect human and animal populations by causing diseases that are often fatal with no known cure.
They have led to significant cattle losses in the past from outbreaks of diseases like mad cow disease.
Prion diseases have an incubation period of several years, making them a long-term threat to human and animal health.