viruses2011
DESCRIPTION
TRANSCRIPT
Chapter
Viruses
Ch 19
Viruses
Characteristics of Viruses
1. Tiny, nonliving particles a. do not respire, move, grow
2. Must reproduce inside of a host
3. Pathogens: disease-causinga. Virulence: degree of
response caused in a host
4. Not given latin names a. named for disease caused,
organ infected, or region first detected in
Viral Structure
1. Inner core of nucleic acid surrounded by protein coat called capsid a. head contains either DNA or RNA
body
T4 BacteriophageTobacco Mosaic
Virus Influenza Virus
Head
Tail sheath
DNA
Tail fiber
RNACapsid
Surfaceproteins Membrane
envelope
RNA
Capsidproteins
Section 19-3
Figure 19-13 Virus Structures
Go to Section:
Recognition & Attachment of Viruses
1. Virus must recognize specific receptor site on host. A. part of the virus matches site
on host B. lands on host and “locks in”
2. Attachment is specific a. virus can enter & reproduce in only a few kinds of cells
Example: tobacco mosaic virus cannot affect human cells even though we are exposed to it.
There are 2 ways viruses can reproduce inside a host.
1. Lytic cycle-fast
2. Lysogenic cycle-slow
Lysogenic Cycle( virus can enter a period of inactivity before becoming lytic)
STEPS
1. Attachment- virus attaches to the host cell
2. Entry- whole virus or just nucleic acid enters the cell
3. Replication- viral nucleic acid joins w/DNA of host cell. It may stay there inactive for years. Host cell continues to divide
If the cell reproduces, the viral nucleic acid is also copied so each new cell is infected.
4. the virus becomes active and enters the lytic cycle.
5. Assembly,lysis, & release- new viral nucleic acids & protein coats are assembled. The virus exits the host cell.
Example- AIDS, Herpes
Bacteriophage proteins and nucleic acids assemble into complete bacteriophage particles
Bacteriophage enzyme lyses the bacterium’s cell wall, releasing new bacteriophage particles that can attack other cells
Bacteriophage DNA inserts itself into bacterial chromosome
Bacteriophage DNA (prophage) may replicate with bacterium for many generations
Bacteriophage DNA (prophage) can exit the bacterial chromosome
Bacteriophage DNA forms a circle
Bacteriophage DNA
Bacterialchromosome
Bacteriophage injects DNA into bacterium
Prophage
Lytic Cycle
Lysogenic Cycle
Section 19-3
Figure 19-15 A Lysogenic Infection
Go to Section:
Section 19-3
Common Diseases Caused by Viruses
Oncogenic viruses
Retroviruses
Adenoviruses
Herpesviruses
Poxviruses
DNA
RNA
DNA
DNA
DNA
cancer
cancer, AIDS
respiratory infections
chickenpox
smallpox
Type of Virus Nucleic Acid Disease
Go to Section:
Go to Section: