Viruses

Are Viruses Living Things? Characteristics of Living things are… Made of cells Can reproduce Based on a universal genetic code Grow and develop Obtain and use materials and energy Respond to the environment Maintain homeostasis As a group, change over time * *

Viral Characteristics NON-LIVING REPRODUCE ONLY WITHIN A HOST CELL by hijacking the cells’ machinery NAMED FOR DISEASE THEY CAUSE OR PLACE THEY INFECT

Which type of cell will be infected by the virus shown below?

Name tells you this virus infects bacteria

Name tells you this virus causes influenza

Viral Size Viruses are very small. If an average virus were the size of an average person, a bacterial cell would be the size of a dinosaur over ten stories tall. Click on the picture for virus size activity

Whiteboard Activity Cell, Virus or Both

Activity: Cell, Virus, or Both? Contains nucleic acid as genetic material Both

Activity: Cell, Virus, or Both? Can grow and develop Cell

Activity: Cell, Virus, or Both? Can only replicate in a host Virus

Activity: Cell,Virus, or Both? Can reproduce on its own Cell

Activity: Cell, Virus, or Both? Obtain and use materials and energy Cell

Activity: Cell, Virus, or Both? Respond to the environment Cell

Activity: Cell,Virus, or Both? Maintain homeostasis Cell

Activity: Cell, Virus, or Both? Can contain DNA Both

Activity: Cell, Virus? Which is smallest? Virus

Activity: Cell, Virus, or Both?

Activity: Cell, Virus, or Both?

Ask students to note similarities and differences that they see in these pictures. Point out that the viruses all contain the same “major parts (i.e. genetic material and capsid), but are specific for specific types of cells. Viruses are typically classified according to the type of organism they infect.

Viral Structure All viruses have: genetic material (DNA or RNA) Capsid: protein coat that enables a virus to enter a living cell

How do viruses infect cells? Once a virus enters a host cell, two different processes can occur: Lysogenic cycle Lytic cycle

Lytic Cycle Click on Picture for Video Virus enters the cell, makes a copy of itself, and causes the cell to burst. Click on Picture for Video

Lytic Cycle viral DNA is injected into the host cell host cell begins to make mRNA from the viral DNA viral proteins shut down the host cell’s regular functions cell is used to make thousands of viruses (DNA and protein coats) host cell bursts (lyses) and releases viruses to infect other cells

Lysogenic Cycle Host cell makes copies of the virus indefinitely. Virus integrates its DNA into the DNA of the host cell, and the viral genetic information replicates along with the host cell’s DNA. Lysogenic viruses remain inactive for a period of time and do not lyse the cell immediately.

Lysogenic Cycle viral DNA is injected into the host cell DNA is integrated into the host DNA host cell divides with the viral DNA as a part of it eventually the viral DNA can be triggered to separate from the host cell DNA and pick up with the lytic cycle at step 2.

Turn to the person next to you and discuss the difference between the lytic and lysogenic cycles.

How do RNA viruses work? RNA viruses do not have built in proofreading, so they mutate and evolve quickly (like the flu). A special kind of RNA virus, called a retrovirus, can cause DNA to be made from their RNA. Certain cancers, and AIDS are caused by retroviruses.