Chapter 19: viruses

What is a virus?

an infectious particle consisting of

genes packaged in a protein coat.

A virus is also an...?

obligate intracellular parasite?

What is an obligate intracellular parasite?

cannot reproduce outside their host cell

Why can a virus not reproduce on its own?

They lack the organelles and materials

How where viruses discovered?

Contagious diseases could be caused by unusually small bacteria causing a disease in tobacco plants purified by Wendell Stanley and called tobacco mosaic virus (TMV).

What can a viral genome be?

Double or single stranded RNA or DNA

What are the two classifications of viruses?

DNA viruses or RNA viruses

What can the genome structure of a virus be?

Single linear or circular molecule of nucleic acid

What is a capsid?

the protein shell

that encloses the viral

genome

What protein subunit forms the capsid?

capsomeres

What are the shapes of viruses?

crystals, icosahedral, helical, complex

What is a viral envelope?

A piece of the host cell's membrane that surrounds the capsid animal viruses.

What do viral envelops contain a combination of?

Viral and host cell molecules

What is a bacteriophage/phage?

Viruses that infect bacteria

What are the characteristics of a bacteriophage?

elongated capsid head that encloses DNA. A protein tail piece that injects phage DNA.

What is a host range?

the spectrum of potential host cells a virus can infect

What happens during viral infection?

viral genome enters cell and is expressed, the cell makes viral proteins which assemble with nucleic acids to create new viruses.

What are the two reproductive mechanisms of a virus?

Lytic cycle and Lysogenic cycle

What is the lytic cycle?

the phage replicates in the cell and then dies.

What is a virulent phage?

A phage that reproduces only by a lytic cycle.

What is the lysogenic cycle?

replication of phage DNA without destroying host.

How does the lysogenic cycle work?

Viral DNA incorporates into host chromosome to be passed to daughter cells.

What is the term for integrated viral DNA?

prophage.

What can cause a bacterial virus to exist the chromosome and trigger the lytic cycle

an environmental trigger

What are the characters of animal viruses?

Envelope and RNA

What is a prion?

infectious proteins that cause degenerative diseases in animals

What is a vaccine?

injection used to stimulate immune system, using harmless derivative of the virus,

preventing illnesses

Why can antibiotics not be used on viruses?

Because they are not bacteria

What is an emerging virus?

those that suddenly become apparent and may cause an epidemic

What can cause a rapidly emergent viral disease?

mutations, small isolated human populations, spread of existing viruses from other animal species (3/4)

What is the term for a global epidemic?

Pandemic

What can cause a an increase in the spread of a virus?

Change in host behavior or change in the environment

What is a vector?

Any living organism that can carry a disease-producing virus

What is the structure of a prion?

incorrectly folded proteins

What does a prion do on the molecular level?

They are able to convert a normal form of a protein into a misfolded version