1. Viruses
Biology 4(C)

2. Title the next blank page: Viruses Put it in your table of contents
On the line underneath the title, write this essential question:
EQ: What are viruses and how are they different from cells?
After this lesson, you will know the structure of viruses, be able to compare viruses to cells, understand viral reproduction, and understand the role of viruses in diseases

3. What is a Virus? Do viruses fulfill the characteristics of life? NO
Viruses cannot reproduce on their own
Need host machinery (ribosomes)
Viruses cannot metabolize energy
Need host energy
No, not considered biotic (a living thing)
Many scientists do not categorize viruses as living. To understand why, remember that living things fulfill all of the characteristics of life.
Viruses cannot reproduce on their own. They must use ribosomes located within the host to make more genetic material and proteins to form more viruses.
Viruses cannot metabolize energy. When a host creates new enzymes, energy located within the host is used.
Because they do not fulfill the characteristics of life, they are not considered a living thing.

4. Viral Structure - Bacteriophage
Viruses have a very different structure than cells. They are much smaller and contain fewer specialized structures. Here is an illustration of a bacteriophage. Bacteriophages, or phages for short, infect bacteria.
The structure at the top is called a capsid. It is a protein shell that encloses the viral genetic material.

5. Viral Structure – Other Types
Viruses that infect animal cells often have membranous envelopes. This allows the virus to attach and fuse to the host’s cellular membrane.

6. Viruses vs. Cellular Life
DNA or RNA
Need a host to replicate
Never contain organelles
Do not convert energy
Cellular Life
Only DNA
Can reproduce independently
Eukaryotes contain organelles
Convert energy to perform tasks
How are viruses and cells different? For starters, some viral genetic information is packaged as RNA. In cells, genetic information is only stored as DNA.
Viruses need a host to replicate within. Cells are capable of reproducing on their own, given nutrients from their environment.
Viruses do not contain organelles like mitochondria or ribosomes, but these organelles are found in their eukaryotic hosts.
Viruses do not convert energy, but cells can convert glucose to ATP molecules for use in cellular tasks like molecular transport.

7. How do cells reproduce? Mitosis = 1 cell becomes 2 Prokaryotes
Eukaryotes

8. Viral Reproduction Viruses need a host to reproduce Two methods
Goal: create more copies of their genetic material
Two methods
Lytic Cycle
Lysogenic Cycle
Even though viruses are not alive, they still reproduce. While cells can do this on their own, viruses need a host cell. The goal is the same, to create more copies of their genetic material.
There are two ways to accomplish this goal. Viruses can use the lytic or lysogenic cycle.

9. Viral Reproduction – Lytic Cycle
Attaches to host
Injects genetic material into host
Cellular machinery duplicates genetic material and creates viral proteins (capsids, tail fibers)
New viruses are assembled
New viruses exit the cell by bursting the cellular membrane
End result – more viruses made, cell dies
Lytic = quick sick!!
During the lytic cycle, a virus attaches to a host and injects its genetic material.
Next, cellular machinery duplicates genetic material and creates viral proteins like capsids and tail fibers. These proteins are assembled into new viruses. Last, the viruses exits the cell by bursting a hole in the host’s cellular membrane.
At the end of the lytic cycle, there are many viruses made and the host cell usually dies from rupture.

10. Viral Reproduction – Lytic Cycle
Here we can see this cycle visually.
Attachment - Attaches to host
Entry - Injects genetic material into host
Replication - Cellular machinery duplicates genetic material and creates viral proteins (capsids, tail fibers)
Assembly - New viruses are assembled
Release - New viruses exit the cell by bursting the cellular membrane

11. Viral Reproduction – Lysogenic Cycle
Attaches to host
Injects genetic material into host
Viral genetic material is inserted into host genome
Viral genetic material lies dormant
When cell reproduces, new copies have viral genetic information
Environmental stimulus sends viral DNA into lytic cycle
End result – more viral genome made, cell lives
Lysogenic = slow and goes undetected for a while
Another method of producing more viral genetic material is the lysogenic cycle. It begins the same, the virus attached to a host and injects its genetic material.
Instead of producing proteins, however, the viral genetic material is inserted into the host genome and lies dormant.
When the host cell reproduces, both daughter cells have a copy of the viral genetic information inside their own genome.
At the last stage of the lysogenic cycle, the cell is still alive, but it and all of it’s daughter cells have viral genetic material lying dormant within their cells.

12. Viral Reproduction – Lysogenic Cycle
Here we can see this cycle visually.
Attachment - Attaches to host
Entry - Injects genetic material into host
Insertion – Viral genetic material is inserted into the host’s genome
Reproduction - New daughter cells contain viral genetic material
Separation – Viral genome sometimes separates from host genome.

13. Viral Reproduction Lysogenic Cycle Lytic Cycle Genome copies made
Cell lives
Lytic Cycle
New viruses made
Cell dies
Viruses can use both cycles
Infect many cells with lysogenic
Create many viruses at once with lytic
Here are the two cycles compared. In the lytic, new viruses are made and the cellular host dies. In the lysogenic, the viral genome is copied through host replication. The host lives, but it is infected.
Some viruses use both cycles to reproduce efficiently. First, they can infect many cells with the lysogenic cycle. Lying dormant, many copies of their genetic material will spread as hosts replicate. When the hosts receive an environmental cue, the lytic cycle begins. Virus proteins are made and burst from their hosts.

14. Common Viral Infections
Lysogenic Cycle:
Herpes
HPV
Chicken Pox (can become shingles)
HIV
Hepatitis B
Lytic:
SARS
Common Cold
Influenza
Rabies
AIDS phase of HIV
Tobacco Mosaic Virus (in plants)

15. Viral Reproduction Lytic & Lysogenic Cycles
This image shows both cycles at once. Remember that a virus can remain in the lysogenic cycle to build dormant viral genomes before shifting to the lytic cycle.

16. Use your notes and fill in the viral reproduction worksheet
The disease AIDS, or acquired immune deficiency syndrome, is characterized by the loss of the immune system. It’s caused by HIV, the human immunodeficiency virus, which makes helper T cells useless.
There is currently no vaccine for the HIV virus. Infection can be prevented by limiting and avoiding transmission.

17. Venn Diagram
Viruses
Bacteria

18. Viruses vs. Bacteria Paper

19. Virus Pamphlet Use your notes and/or your text book pg 478-438
Use the legal sized paper to create a folded pamphlet.
USE COLOR
Must include the following
Your front cover design must have the 3 Virus structures with labels (see pictures on pg 479 or in your notes)
Inside Panel 1 (inside front cover) diagram and label the lytic and lysogenic cycles. Fully draw, color and label all pictures in your pamphlet
On panel 2 of your pamphlet write out question and answer questions 1-5 found at the bottom of page 483