Virus Reproduction

OverviewCycles for reproduction

LyticLysogenic

RetrovirusHIV

Diseases caused by virusesPrevention

Overview

• Viruses must be inside a living cell (host) to reproduce.

• Viruses attack host cells by attaching to their cell membrane and injecting their genetic material into the cell.

Two Cycles for Reproduction

1. Lytic cycle-Characterized by viral infection, replication, and cell destruction

2. Lysogenic cycle-the viral genome replicates without destroying the host cell

Cycles for Reproduction:The Lytic Cycle

1. Viral DNA/RNA injected into the cell

2. Viral DNA/RNA replicates to produce new viruses inside the host cell

3. Soon the cell is full of new viruses that burst from the cell spreading the disease

It’s not just bacteriophages that do this…

Cycles for Reproduction:The Lytic Cycle

1. Virus attaches to host2. Virus enters cell (nucleic

acid is injected) 3. Replicates IMMEDIATELY 4. Produces many new

viruses5. Viruses burst from the

cell to invade other cells (This is what harms/kills the cell)

Cycles for Reproduction:The Lysogenic Cycle

1. Virus inserts its DNA into its host DNA and it “hides” there

2. Becomes a provirus/prophage3. Divides/replicates with the “help”

of the host cell4. ALL WITHOUT HARMING THE CELL5. Later it will begin the lytic cycle

to spread the virus

Cycles for Reproduction:The Lysogenic Cycle

1. Virus invades cell2. Does not immediately kill host

cell3. Becomes part of host’s DNA4. Host cell reproduces as usual

(making more viral DNA without knowing it)

5. Eventually goes into the lytic cycle to spread the virus

Retrovirus• Viruses that get their genetic

information copied backwards…– From RNA to DNA

• Virus that contains RNA• When the virus infects the cell, they

produce a DNA copy of their RNA• Responsible for some types of cancer in

animals• HIV is a common example

RetrovirusHIV

HIV- Human immunodeficiency virusExterior wall made of glycoproteinHIV binds to human immune cells at

specific receptor sites

RetrovirusHIV

Can result in the disease AIDSCan hide for years in the nucleus of T-cells

(white blood cells that help fight infection) in the Lysogenic cycle

People can have no symptoms, yet be spreading the disease to many partners.

RetrovirusHIV

HIV then begins the Lytic cycle and T-cells begin to die.

The patient eventually dies from another disease (opportunistic infection)

There are not enough T-cells to help fight infection.

This can lead to AIDS (when T cell count is below 200 cells/ml).

Diseases Caused by Viruses

• Adenovirus (common cold)

• AIDS• Avian Bird Flu• Chickenpox• Ebola• Hepatitis A & B

• Influenza (Flu)• Mumps• Polio• Rabies• SARS• Smallpox• Warts• West Nile

Preventiono Antibiotics won’t cure viral diseases!

(The Doctor can’t cure your cold! Only your symptoms are treated.)

o Some viruses can be prevented by Vaccines which help your own immune system fight the disease.

o Edward Jenner developed the first vaccine from cowpox.

Prevention

Vaccines for smallpox, a deadly virus, helped wipe it out.

Other diseases that can be prevented by vaccines are:

o Polioo Measleso Mumps

o Influenza