1. 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?

2. A virus is an infectious agent made up of
nucleic acid (DNA or RNA) wrapped in
a protein coat called a capsid.
Bacteriophage
Influenza (Flu)
DNA = Genetic material = RNA
Capsid
(Protein Coat)
Tail sheath
Envelope
(Lipids & Glycoproteins)
Tail
fiber

3. Can viruses infect any cell?
Viruses can only attack certain cell types. They are said to be HOST specific.
Example:
The rabies virus only attacks brain or nervous cells.
It’s like the pieces of a puzzle. The ends have to match up so only certain pieces fit (“Lock & Key” fit).

4. Ex. Bacteriophage virus infect bacterial cells only.

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

6. Antigens = Surface markers (proteins)
Bacteriophage
Influenza (Flu)
Antigens
spike like projections
(Glycoproteins)

7. Viruses vs. Cells (structure)
DNA or RNA
Capsid (protein coat)
No organelles
No cytoplasm
DNA and RNA
Organelles
Cytoplasm

8. Are viruses alive? Made of one or more cells?
Non-cellular - NOT organisms
Grow and develop? No
Eat for energy? No
Metabolize nutrients? No
Respond to stimuli? No No
Maintain homeostasis?
Adapt to environment? (change over time)
Yes – viruses can mutate (change). Ex. Influenza-new vaccine every year
Reproduce?
Yes
Reproduce on their own?
No – need a host.
Viruses share some characteristics of living things, but need to meet all criteria to be considered living.

9. Are viruses living? NO TWO
How many characteristics of life do viruses possess?
TWO
*Genetic Material
*Change over time
Are viruses living? NO

10. Viruses are parasites What is a parasite?
Parasite is an organism that depends entirely upon another living organism (a host) for its existence in such a way that it harms that organism.
Ex. A flea is a parasite to a dog and is harmful to the dog.

11. Viruses must have a living host to reproduce.
Viruses are parasites
Viruses must have a living host to reproduce.
Viruses hijack a living cell’s machinery and use it to reproduce more virus particles.

12. Viruses are pathogens What is a pathogen?
Pathogen is any agent that causes diseases.

13. Two stages of viral reproduction
An active, infectious stage. It is called a Lytic infection.
Ex. Influenza (Flu virus)
A dormant (sleeping) stage. It is called a Lysogenic infection.
Ex. HIV
(Human Immunodeficiency Virus)

14. Lytic vs. Lysogenic Cycles

15. LYTIC CYCLE
Viral DNA is injected into cell. Bacterial DNA is destroyed.
Viral DNA is copied & viral parts are made.
Virus attaches to cell.
Step 3
Step 2
Step 1
Viral parts are assembled
Cell bursts (lyses) and releases new viruses.
Viruses spread.
Step 4
Step 5

16. LYTIC CYCLE
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.)

17. Checkpoint What does “lysis” mean?
What are the stages of the lytic cycle?
What does “lysis” mean?
What is the result of the lytic cycle?

18. LYSOGENIC CYCLE Some viruses like HIV do NOT go straight into the lytic cycle. These viruses enter a long (dormant) period - between an infection and the onset off disease.
= prophage (viral DNA)

19. LYSOGENIC CYCLE
Virus enters a long (dormant) period between an infection and the onset off disease.
Viral genetic material (DNA) incorporates into a host’s DNA and called a prophage.
Virus replicates its genetic material without destroying the host.
Every time the host divides, it copies the viral DNA and passes the copies.
Various factors such as UV light can trigger a virus to enter the LYTIC CYCLE  cell bursts

20. Lytic vs. Lysogenic Cycles
Rapid: Causes disease right away
Ex. Influenza
Does NOT involve integration of viral genetic material into the host genetic material.
Result in host destruction:
Host cell lyses (bursts)
Long period between infection and onset off disease (dormant period). Ex. HIV
Involves integration of viral genetic material into the host’s genetic material forming a prophage.
Eventually enters the Lytic Cycle and host cell lyses.

21. What does “dormant” mean?
Checkpoint
What does “dormant” mean?
Which infection (cycle) involves integration of viral DNA into the host’s DNA?
Which infection (cycle)results in cell lysis (cell bursting)?
Which infection (cycle)causes disease right away?

22. Types of Viruses Viruses have either DNA or RNA but NOT both.
Viruses with RNA are called retroviruses.
Examples:
HIV Influenza (Flu)

23. HIV (Human Immunodeficiency Virus) most deadly human virus ever
HIV is a lysogenic virus. What does it mean to be “lysogenic”?
Long period between infection & onset of disease.
HIV has 2 copies of RNA.
Is a retrovirus
(RNA  DNA)

24. HIV HIV causes AIDS. Acquired Immune Deficiency Syndrome
HIV attacks the immune system.
If HIV has reduced the immune system function, an individual is at risk of life-threatening infections and diseases such as pneumonia and cancer. Your body is unable to fight off infection and diseases.
HIV can be transmitted through blood –to-blood contact and sexual activity (exchange of sexual fluids and blood).

25. HIV What cells of the immune system does HIV target?
HIV infects only certain white blood cells:
Helper T cells

26. Helper T-cell operates as a judge that identifies infections and “orders” their destruction to other white blood that make ANTIBODIES  bloodstream  combat invading pathogen such as viruses and harmful bacteria.

27. Each antibody recognizes a specific antigen unique to its target.
What are antibodies?
Antibodies are proteins used by the immune system to identify and neutralize foreign invaders such as viruses and harmful bacteria.
Each antibody recognizes a specific antigen unique to its target.

29. Causes disease—pathogenic Disease producing agent—pathogen
*Harmful Viruses
Causes disease—pathogenic
Disease producing agent—pathogen
Human Diseases:
Warts, common cold, Influenza (flu), Smallpox, Ebola, Herpes, AIDS, Chicken pox, Rabies

31. How can viruses be prevented?
Viruses disrupt the body’s normal equilibrium/balance (homeostasis)
Viruses can be prevented with vaccines, but NOT treated with antibiotics.
(antibiotics treat bacteria)
WHAT IS VACCINE?
Weakened virus

33. *Viruses can help cells, too
Beneficial:
Genetic Engineering—harmless virus carries good genes into cells. Replace faulty or missing genes in a cell.