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

capsid nucleic acid

lipidenvelope

surfaceproteins

capsid

nucleic acid

lipid envelope

Surface proteins

capsidsurfaceproteins

nucleic acid(rabies)

(foot-and-mouthdisease)

(influenza)

1. Enveloped

2. Helical

3. Polyhedral

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.

colored SEM; magnifications:large photo 25,000; inset 38,000x

– bacteriophages pierce host cells

18.2 Viral Structure and Reproduction

- viruses of eukaryotes enter by endocytosis and also fuse with membrane

18.2 Viral Structure and Reproduction

host bacterium

The bacterophage attachesand injects it DNA into a host bacterium.

The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells.

The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages.

The viral DNA forms a circle.

Viruses cause two types of infections.

• A lytic infection causes the host cell to burst.

The virus may enter thelysogenic cycle, in which thehost cell is not destroyed.

18.2 Viral Structure and Reproduction

• A lysogenic infection does no immediate harm.

The viral DNA is called a prophagewhen it combines withthe host cell’s DNA.

Although the prophage is notactive, it replicates along withthe host cell’s DNA.

Many cell divisions produce acolony of bacteria infectedwith prophage.

The prophage may leave thehost’s DNA and enter thelytic cycle.

18.2 Viral Structure and Reproduction

Viral Diseases

• 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• Vaccines• Wash hands/ Good hygiene

• Cough/ Sneeze in tissue/ sleeve

• Disinfectants (breaks apart capsid/RNA)