Chapter 19: Viruses Flashcards
Capsid
Protein shell enclosing the viral genome built from protein subunits called capsomeres
Capsid structure
Helical- a single type of protein arranged in a helix; rod-shapped
Polyhedral- e.g. icosahedral: have 20 identical triangular faces
Viral envelopes- have a membranous envelope surrounding capsid that is derived from the membranes of the host cell
Bacteriophage- complex consisting of an icosahedral head and with a tail apparatus that has fibers which allow it to attach to a host target cell
Host range
The limited range of host species that a virus is able to infect
Result of recognition system that allows viruses to identify host cells via receptor molecules on the outside of the cell
Lytic cycle
Replicative cycle that culminates in the death of the host cell
During the late stage of the infection the host cell lyses and releases the phages that were produced within the host cell
Lysogenic cycle
Allows replication of the phage genome to proceed without killing the host
The viral DNA known as a prophage is embeded into the host cell’s genome
Virulent phage
A phage that replicates only via the lytic cycle
Temperate phage
A phage capable of using both the lytic cycle and the lysogenic cycle
Restriction enzymes
Bacterial enzymes that recognize foreign DNA and detroy it
Viral envelope formation
ER ribosomes produce envelope glycoproteins that are finished by the Golgi apparatus and subsequently embedded in the host cell membrane
New viral capsids are secreted via exocytosis wrapped in membrane that has glycoproteins embedded in it
Reteroviruses
Have an enzyme called reverse transcriptase that transcribes a segment of DNA from and RNA template
Newly made DNA enters the nucleus and integrates into the DNA of a chromosome; integrated viral DNA is called a provirus
Prions
Infectious proteins that cause degenerative brain diseases in animals due to an aggregation and accumulation of prions
What are viroids
Tiny molecules of circular RNA that infect plants.
