Transcript 18.2 Viral Structure and Reproduction

18.2 Viral Structure and Reproduction
Viruses exist in a variety of shapes and sizes.
18.2 Viral Structure and Reproduction
– Simple and small pathogen
– Made of Capsid and RNA or DNA
– Non living (must infect living cells)
18.2 Viral Structure and Reproduction
Shapes
(foot-and-mouth
disease)
(influenza)
1. Enveloped
capsid
3. Polyhedral
nucleic acid
lipid
envelope
surface
proteins
surface
proteins
(rabies)
2. Helical
Surface proteins
capsid
nucleic acid
lipid envelope
capsid
nucleic acid
18.2 Viral Structure and Reproduction
4. Bacteriophages- viruses that infect bacteria.
capsid
DNA
tail sheath
tail fiber
18.2 Viral Structure and Reproduction
Viruses enter cells in various ways.
– bacteriophages pierce host cells
colored SEM; magnifications:
large photo 25,000; inset 38,000x
18.2 Viral Structure and Reproduction
- viruses of eukaryotes enter by endocytosis and also
fuse with membrane
18.2 Viral Structure and Reproduction
Viruses cause two types of infections.
• A lytic infection causes the host cell to burst.
host bacterium
The bacterophage attaches
and injects it DNA into a host
bacterium.
The host bacterium breaks apart,
or lyses. Bacteriophages are able
to infect new host cells.
The viral DNA
forms a circle.
The viral DNA directs the host
cell to produce new viral parts.
The parts assemble into new
bacteriophages.
The virus may enter the
lysogenic cycle, in which the
host cell is not destroyed.
18.2 Viral Structure and Reproduction
• A lysogenic infection does no immediate harm.
The prophage may leave the
host’s DNA and enter the
lytic cycle.
The viral DNA is called a prophage
when it combines with
the host cell’s DNA.
Many cell divisions produce a
colony of bacteria infected
with prophage.
Although the prophage is not
active, it replicates along with
the host cell’s DNA.
18.2 Viral Structure and Reproduction
Viral Diseases
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Common Cold – contaminated objects
Influenza – respiratory droplets (sneeze)
HIV/AIDS – body fluids
Chicken Pox – respiratory droplets (sneeze)
Hepatitis B – contaminated blood/ body fluids
West Nile Virus - mosquitoes
HPV – sexual contact (causes cancer)
Small Pox – respiratory droplets
Mumps – respiratory droplets
Measles – respiratory droplets
Food Poisoning – eating bad food
18.2 Viral Structure and Reproduction
Virus Prevention
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Vaccines
Wash hands/ Good hygiene
Cough/ Sneeze in tissue/ sleeve
Disinfectants (breaks apart capsid/RNA)