1. By, Mackenzie Pabst
Viruses; Section 18-1

2. What is a Virus?
disease-causing, nonliving particle composed of an inner core of nucleic acids surrounded by a capsid
A virus replicates inside living cells called host cells

3. What is a Capsid?
Outer coat of proteins that surrounds a virus' inner core of nucleic acids
The arrangement of the capsid’s proteins determine the virus' shape

4. Why are Viruses Non-Living?
Viruses are nonliving because:
They don't exhibit all the criteria for life
Criteria for life includes:
Respiration, growth and development
All viruses can do is replicate
Replication is making exact copies of themselves with the help of living cells

5. How are Viruses Named?
Some Viruses are named after the disease they cause
Example: Rabies Virus
Other viruses were named for the organ or tissue they infect.
Example: The Adenovirus effects the adenoid tissue
Rabies Virus

6. How does a Virus attach to a Host Cell?
For a virus to replicate, it must enter a host cell
When a virus’ proteins interlock with the receptor site, the virus is attached to its host cell
The attachment process is like two pieces of a jigsaw puzzle fitting together

7. Virus Attachment
Each virus has a specifically shaped attachment protein
Viruses are species specific
Some Viruses are cell-type specific
Example: polio viruses normally infect only intestinal and nerve cells.

8. A Viral Replication Process
Lytic Cycle:
A Viral Replication Process
Attachment: The Virus attaches to the Host Cell
Entry: The Bacteriophage injects its nucleic acid into the bacterial cell
Replication : The host’s metabolic machinery makes the virus’ nucleic acid and proteins

9. Bacteriophage Also known as a phage
Is a viruses that infects and destroys bacteria

10. A Viral Replication Process
Lytic Cycle:
A Viral Replication Process
D. Assembly: New Virus Parts are made
E. Lysis and Release: The host cell breaks open and releases new viruses
This results in the killing of the host cell

11. Another Viral Replication Process…
Of an Enveloped Virus:
After attachment, the membrane of the host cell surrounds the virus
This produces a virus- filled vacuole inside the host cell's cytoplasm.
The virus bursts out of the vacuole and releases its nucleic acid into the cell.

12. The Lysogenic Cycle

13. The Lysogenic Cycle: Begins the same way as the Lytic Cycle
The virus attaches to the host cell and its nucleic acid is injected into the cell.
Then the viral DNA is integrated into the host cell's chromosomes
This is done instead of immediately taking over the host's genetic material (As in the Lytic Cycle)
This Cycle does not kill its host cell

14. RNA Viruses: Many Viruses, including HIV, are RNA viruses
This means their only nucleic acid is RNA
The RNA virus with the most complex replication cycle is the Retrovirus
The Retrovirus - uses reverse transcriptase to make DNA from viral RNA
the retroviral DNA is then integrated into the host cell's chromosome

15. Reverse Transcriptase:
Is an enzyme carried in the capsid of a retrovirus that helps produce viral DNA from viral RNA
If this enzyme is found in a person, it is evidence for infection by a retrovirus

16. Retrovirus Cycle:

17. Retrovirus Cycle:
Once inside a host cell, the retrovirus makes DNA from its RNA with reverse transcriptase
Reverse transriptase produces double- stranded DNA from the viral RNA.
The double-stranded viral DNA becomes part of the host cell’s chromosome and it becomes a provirus

18. Provirus: viral DNA that is integrated into a host cell's chromosome
It is replicated each time the host cell replicates

19. Human Immunodeficiency Virus (HIV)
HIV infects white blood cells in humans
The infected cells still function normally
Because the viral genetic material is a provirus that only produces a small number of new viruses at a time
An infected person will not appear sick
Can infect others with the virus through body fluids

20. Human Immunodeficiency Virus (HIV)
Most people with HIV will get AIDS
Over time, more white blood cells are infected and killed
White Blood cells are essential to our immune system
Their destruction reduces the body’s ability to protect itself from other viruses

21. Virus’ link to Cancer:
Some viruses have been linked to certain cancers in humans and animals
Viruses can disrupt the normal growth and division of cells in a host
This causes abnormal growth and creates tumors

22. Prions:
Are composed of proteins but have no nucleic acid to carry genetic information
Are thought to act by causing other proteins to fold themselves incorrectly, resulting in improper functioning
Responsible for many animal diseases
Example: Mad Cow Disease

23. Viroids:
Composed of a single circular strand of RNA with no protein coat
Shown to cause infectious diseases in several plants.
Have less RNA than most viruses

24. Plant Viruses: There are more than 400 plant viruses
Plant Viruses can cause stunted growth and yield losses in their host plants.
The first virus to be identified as a plant virus was the tobacco mosaic virus

25. Plant Viruses: Do not undergo lytic or lysogenic phases
Plant Viruses are named according to their host plant.
Not all viral plant diseases are fatal or even harmful.
The Mosaic virus, as seen in the following picture, cause patterns of color in the flowers of plants.