Viruses, Viroids, and Prions

Page
4

Prions are “infectious proteins”

They are normal body proteins that get converted into an alternate configuration by contact with other prion proteins

They have no DNA or RNA

The main protein involved in human and mammalian prion diseases is called “PrP”

Slide 43

Prion Diseases

Prions form insoluble deposits in the brain

Causes neurons to rapidly degeneration.

Mad cow disease (bovine spongiform encephalitis: BSE) is an example

People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies

Slide 44

Viral Replication

Slide 45

Viral Attack

Viruses are very specific as to which species they attack

HOST specific

Humans rarely share viral diseases with other animals

Eukaryotic viruses usually have protective envelopes made from the host cell membrane

Slide 46

5 Steps of Lytic Cycle

1. Attachment to the cell

2. Penetration (injection) of viral DNA or RNA

3. Replication (Biosynthesis) of new viral proteins and nucleic acids

4. Assembly (Maturation) of the new viruses

5. Release of the new viruses into the environment (cell lyses)

Slide 47

Bacteriophage Replication

Bacteriophage inject their nucleic acid

They lyse (break open) the bacterial cell when replication is finished

Slide 48

Lytic Cycle Review

Attachment Phage attaches by tail fibers to host cell

Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell

Biosynthesis Production of phage DNA and proteins

Maturation Assembly of phage particles

Release Phage lysozyme breaks cell wall

Slide 49

Attachment: Phage attaches to host cell.

Penetration: Phage pnetrates host cell and injects its DNA.

Merozoites released into bloodsteam from liver may infect new red blood cells

1

2

3

Bacterial cell wall

Bacterial chromosome

Capsid

DNA

Capsid

Sheath

Tail fiber

Base plate

Pin

Cell wall

Tail

Plasma membrane

Sheath contracted

Tail core

Slide 50

4

Maturation: Viral components are assembled into virions.

Tail

5

Release: Host cell lyses and new virions are released.