10.3

Viruses

Warm up

What is a prokaryote?Is it a living or non-living?How does a prokaryote resemble the eukaryote?

Introduction • Can you identify the following structure?

• Is it considered living or non-living?

Objectives • Explain how viruses are similar to and different

from living things.• List the four major virus shapes.• Describe the two kinds of viral reproduction.

Who am I????????????• One day, you discovered red spots on your skin.

More and more red spots appear and they begin to turn into itchy blisters. What do you have???

• Chicken pox is caused by a virus.

• A virus is a microscopic particle that gets inside a host cell and often destroys the cell.

Characteristics of Viruses• Viruses are tiny (5 billion virus could fit in one blood drop.

• Change rapidly (effect on living things can change)

• Scientists don’t know exactly how many types of viruses exist.

• They are difficult to fight because of the above properties.

• Strictly speaking, they are non-living.

• Viruses contain protein and genetic material

• Their genetic material can be either RNA or DNA

Characteristics of Viruses• Viruses can’t eat, drink, grow, break down food or use oxygen.

• Can’t function by its own.

• Can reproduce only inside a living cell that serves as a host.

• Host: a living thing that a virus or parasite lives on or in.

• Viruses use host cells as factories and force host cells to make viruses rather than new cells

Classification of viruses• Viruses may be classified by their:

1- shape

2- the kind of disease they cause

3- their life cycle

4- genetic material

Basic shapes of viruses

Genetic material and type of disease

• The genetic material of a virus can be either RNA or DNA.

• The genetic material of the virus determines what disease is caused by that virus.

• Viruses that cause warts and chickenpox have DNA as their genetic material.

• Viruses that cause cold, flu and AIDS have RNA as their genetic material.

Life cycle of a virus• The one thing that viruses do which living things can

also do is to make more of themselves.

• The life cycle of a virus can be described either as:

1- lytic cycle2- lysogenic cycle

Lytic cycle

Lysogenic cycle

• In the lysogenic cycle, the genes of a virus are incorporated into the genes of the host cell.

• To reproduce, a virus must enter a cell, reproduce itself, and then break open the cell. This is called the lytic cycle

Life cycle of a virusLytic cycle Lysogenic cycle

Wrap up • Viruses have characteristics of living and nonliving

things. They reproduce in living cells.• Viruses may be classified by their shape, the kind of

disease they cause, or their life cycle.• To reproduce, a virus must enter a cell, reproduce

itself, and then break open the cell. This is called the lytic cycle.

• In the lysogenic cycle, the genes of a virus are incorporated into the genes of the host cell.

Assignments • Quiz 2 next Sunday:

10.2: Bacteria’s role in the world

10.3 Viruses