1. Compare the structures and functions of viruses to cells
Today’s Objective:
Compare the structures and functions of viruses to cells

2. Viruses Doesn’t belong to any kingdom -It’s not a plant or an animal.
-It’s not a fungi, protist, or bacteria.
WHAT IS A VIRUS?

3. A virus is an infectious agent made up of nucleic acid (DNA or RNA) wrapped in a protein coat called a capsid.
Viruses have no nucleus, no organelles, no cytoplasm or cell membrane—Non-cellular
This is why it does NOT belong to any kingdom. vs

4. Viruses with RNA that transcribe into DNA are called retroviruses.
Viruses have either DNA or RNA but NOT both.
Viruses with RNA that transcribe into DNA are called retroviruses.
Viruses are parasites—an organism that depends entirely upon another living organism (a host) for its existence in such a way that it harms that organism.
HIV Infected Cell
(This is the reason why HIV is so incurable.)
A flea is a parasite to a dog and is harmful to the dog.

5. Section 18.1 Summary – pages 475-483
Viruses are extremely small “non-living” particles composed of genetic material (DNA or RNA) enclosed in a protein coat.
They are smaller than the smallest bacteria.
Bacteriophage Viruses
Flu Viruses
Section 18.1 Summary – pages

6. Section 18.1 Summary – pages 475-483
What is a Virus?
Viruses are considered NON-LIVING because:
They cannot metabolize food for energy
They are NOT cells
All viruses can do is replicate—make copies of themselves—with the help of living cells…a HOST CELL.
Section 18.1 Summary – pages

7. Bacteriophage—viruses that infect bacteria
Capsid (protein coat)
inside contains either
RNA or DNA
2. Flu (influenza), HIV
DNA or RNA
Surface Marker

8. D. Replication is how a virus spreads.
A virus CANNOT reproduce by itself—it must invade a host cell and take over the cell activities, eventually causing destruction of the cell and killing it. (The virus enters a cell, makes copies of itself and causes the cell to burst releasing more viruses.)
DNA/RNA is copied.
DNA/RNA injected into cell.
Virus attaches to cell.
Step 3
Step 2
Step 1
Virus copies itself.
Cell bursts (lyses) and releases new viruses.
Step 4
Step 5

9. Some viruses hit you fast
The lytic cycle is a viral replication cycle in which a virus:
1. takes over a host cell’s DNA
2. uses the host cell’s structures and energy to replicate the virus
3. then the host cell bursts(lyses), dies, and releases the replicated viruses.

10. Some viruses slowly sneak up on you…
A lysongenic cycle begins in the same way as a lytic cycle.
However, in a lysogenic cycle, instead of immediately taking over the host’s genetic material, the viral DNA is integrated into the host cell’s chromosome.

11. Section 18.1 Summary – pages 475-483
The Lysogenic Cycle
Viral DNA that is integrated into the host cell’s chromosomes is called a provirus.
Every time the host cell reproduces, the provirus is replicated along with the host cell’s chromosome.
This can go on for years…
Section 18.1 Summary – pages

12. Section 18.1 Summary – pages 475-483
Once the virus is ready to take over other cells….
Lysis, the bursting of a cell…Result: Cell Death
Section 18.1 Summary – pages

13. In the lytic cycle, the virus reproduces itself using the host cell's chemical machinery.

14. In the lysogenic cycle, the virus reproduces by first injecting its genetic material, integrating it’s DNA into that of the cell’s.

15. Certain viruses can only attack certain cell types
Certain viruses can only attack certain cell types. They are said to be specific.
Example: The rabies virus only attacks brain or nervous cells.
Surface Markers
Virus
Receptor Sites
It’s like the pieces of a puzzle. The ends have to match up so only certain pieces fit.
Cell

16. A virus recognizes cells it can infect by matching its surface marker with a receptor site on a cell.
Virus
Surface Markers
Cell
Receptor Sites

17. Importance: Beneficial: *Harmful Causes disease—pathogenic
Disease producing agent—pathogen
Human Diseases: Warts, common cold, Influenza (flu), Smallpox, Ebola, Herpes, AIDS, Chicken pox, Rabies
Viruses disrupt the body’s normal equilibrium/balance
Viruses can be prevented with vaccines, but NOT treated with antibiotics.
(antibiotics treat bacteria)
Beneficial:
Genetic Engineering—harmless virus carries good genes into cells.

18. Virus Living Cell RNA or DNA core (center), protein coat (capsid)
Cell membrane, cytoplasm, genetic material, organelles
Structure
Copies itself only inside host cell--REPLICATION
Asexual or Sexual
Reproduction
DNA and RNA
Genetic Material
DNA or RNA
Growth and Development NO
YES—Multicellular Organisms
Obtain and Use Energy NO
YES
Response to Environment
YES NO
Change over time NO
YES

19. Are viruses living? NO ONE
How many characteristics of life do viruses possess?
ONE
*Genetic Material
Are viruses living? NO

20. A cell in which a virus replicates inside of is called the host cell.