Warm-UpWhat makes something alive?

Is the common cold a virus or a bacteria?

When is your project (Data Table and Graphs) due?

How the flu invades your body!

Video

Video

I. What is a virus?

- a virus is a tiny particle made of protein and genetic information

electron micrograph of a cluster of influenza viruses

Head/ CapsidGenetic

material

Tail fibers

Basic Virus Structure

A virus has 2 parts

1) genetic material -

a) the genetic information in viruses may be either RNA or DNA.

2) Capsid a) the Capsid is a shield made of protein that protects the genetic material.

Bacteriophage – a virus that attacks bacteria

Capsid

II. What Do Viruses Do?

- viruses inject other cells with their genetic material in order to reproduce

-each type of virus infects a particular kind of cell in a specific organism

-the specific organism that a virus attacks is called its host

III. How Do Viruses reproduce?

REPLICATION

Steps of Lytic Viral Replication

1. The virus attaches to a host cell

                                

2. The virus injects its information into the host cell

3. The genetic information of the virus takes control of the host cell and orders the production of new viruses

             

4. New viruses are assembled in the host cell 5. So many viruses are made inside the host cell that the cell bursts (lysis)

6. The new viruses leave the host cell and go on to infect new cells.

LYSOGENIC Replication is a little different…

The first two steps are the same. After the virus injects its information into the host cell, the viral DNA becomes part of the host DNA.

Every time the host cell goes through cell division, the viral DNA is replicated and is inside each new daughter cell.

Eventually, the virus goes back into the lytic cycle step – hijacking the host’s machinery and making more viruses but now the virus is in a ton of host cells!

HIV vs Flu Influenza reproduces through the lytic cycle

HIV reproduces through the lysogenic cycle

Virus vs Cell Venn Diagram

Similarities: genetic material, protective coating, can reproduce.

Differences: cell reproduces without a host, virus only reproduces with a host, cell has organelles/nucleus/cell membrane, virus has a capsid, cell is alive, virus is not

Review Virus Video

Mythbusters

It's easy to mix these up since compared to us, both are VERY SMALL.

But...  

Bacteria, given the proper nutrients, can grow and reproduce on their own

Viruses cannot "live" or reproduce without getting inside some living cell, whether it's a plant, animal, or bacteria.

 

compared to viruses,

bacteria are HUGE

◦ Antibiotics are often used to fight off bacterial infections

◦ Since a virus is not a living cell, antibiotics used to fight living bacteria will not be effective on viral illnesses

Should you still take an antibiotic “just in case” or to help relieve your symptoms?

◦ NO!!!

◦ This will only lead to antibiotic resistance of your immune system, causing you to get sicker in the future

Check-Point Questions Write these in your notebooks.

1. What do viruses depend on for their reproduction?

2. Describe each of the two reproductive paths viruses may follow once

they have entered a cell.

3. What’s the difference between bacterial and viruses?

4. What do antibiotics kill?

Quick review 1. What do viruses depend on for their reproduction? Viruses depend on living cells for

reproduction.

2. Describe each of the two reproductive paths viruses may follow once they have entered

a cell. In a lytic infection, viral genes are quickly transcribed and new viruses are made by

the host cell. In a lysogenic infection, the host cell is not immediately taken over; viral

nucleic acid is inserted into the host cell’s DNA and may be inactive for a long time.

3. What’s the difference between bacterial and viruses?

Bacteria are one-celled organisms; viruses must be inside a cell to live

4. What do antibiotics? Bacteria