Virus

While the Modern Cell Theory says that all livings are made of cells, viruses basically aren't clasified as living beings as they lack many traits for life. Viruses aren't bacteria, fungi, nor prokaryotes or eukaryotes as it's not as a cell neither.

Shapes

Viruses differ from shapes. Some can be helical shape like the ebola virus or polyhedral shapes like the influenza virus. Others have more complex shapes like bacteriophages

Replication

Viruses can only reproduce by hijacking a host cell and to one of the following cycles once inside the host cell:

• Lytic cycle = virus is active, symptoms occur

  • • Viral reproduction occurs, cells burst

• Lysogenic cycle = virus is dormant, no symptoms occur

• reproduction does not immediately occur as viral DNA is integrated with the host genome (prophage)

• These latent viruses may remain inactive for multiple years

• e.g. herpes (cold sores), HIV, varicella zoster (chicken pox virus that can lay dormant and come out as shingles years after initial disease)

HIV

Some like HIV are viruses that lead to aids. They bind to a CD4 glycoprotein that's found on specific cells' surfaces like helper T cells, which are crucial for protecting our immune systems. As HIV target helper T cells, can make someone vulnerable to other infections. 

There are some medications to fight HIVs by preventing them from attaching their genetic materials.

However, HIVs and other viruses can mutate and fight back the medications. 

Pesticide

Since viruses go after insects, they're used for pesticide but can still have cons.

Importance

They're crucial in ecosystems by controlling the population of other organisms

Classification and Phylogeny

Viruses are classifed based on RNA or DNA virus, presense of an envelope, Capsi/protein coat's shape, or host they infect. About 4k have been classified but millions are speculated to exist. Of the 80 known virus families, 21 cause disease to humans.

Naming methods

Type

Hypothized origins

• Originated as small infectious cells that lost their cytoplasm and ability to reproduce outside a living cell

• Originated as “escaped” fragments of DNA

• Virus-like particles existed before the first cells

Vaccines

A weakened form of a virus is injected

This triggers an immune response but not illness

The ‘antibodies’ are stored in memory in case of contact with the true form of the virus

e.g. 2006 a vaccine was created for human papillomavirus (HPV)

(HPV was a leading cause of cervical cancer)

It is not always possible to develop effective vaccines for some diseases (e.g. HIV )

Some viruses are constantly changing so vaccinations are needed often e.g. influenza

Viroids

Prions

Abnormally folded “infectious proteins” in the brain and nervous system They convert normal prion proteins into abnormal ones How it spreads: when an animal eats an infected organism, these proteins travel through the bloodstream to the brain and affect other proteins e.g. Mad cow disease (bovine spongiform encephalitis: BSE) (results in spongy holes in brain of cows) Humans who eat infected meat develop Creutzfeldt-Jakob disease (CJD)

Viroids

Small, circular RNA molecules without a protein coat (or capsid) 

Pathogens of higher plants e.g. Potato spindle tuber viroid causes stunting of plants and elongated tubers