1. Viruses
Biology I

2. Characteristics Size Extremely tiny
½ to 1/100 the size of the smallest bacterial cell.

3. Characteristics NON-living No growth No metabolic processes
Cell respiration, etc.
Reproduction cannot occur outside of a host cell
Host cell – cell in which a virus reproduces

4. Characteristics Names Different naming because they are NON-living
NO latin
Named for disease caused or tissue infected
Rabies; polio
adenoviruses
Bacteriophages

5. Structure Inner Core of NUCLEIC ACID Virus’s genetic material
DNA or RNA
Genes code for making copies of virus!
Outer coat
Protein
CAPSID
Protects nucleic acid
Shape is important
Envelope
Only in some larger viruses (animal)
Human flu virus

7. Shape is Important to Virus’s Ability to Infect
Receptor sites
On cells
Receive specific molecules the cell needs
Protein coats of viruses designed to fit receptor sites on cells
Allows virus to recognize and infect host
Makes viruses specific to a cell type
If the virus MUTATES, then it may be able to infect a different cell

8. LYTIC CYCLE Virus lands and attaches to cell
Virus injects nucleic acid into cell
Host cell DNA is destroyed
Viral genes hijack cell and force it to make more viral DNA and capsids
Viral components are assembled into new viral particles
Cell undergoes LYSIS (bursts) and viruses come out
Virus particles can then infect more cells
90 minutes > 200 new viruses

10. Lysogenic Cycle
Virus infects but does NOT immediately kill cell

11. Lysogenic Cycle Virus attaches Virus injects genetic material
Viral DNA becomes part of host cell’s OWN DNA.
Every time the host cell reproduces it makes new cells containing the viral DNA (provirus)
This can go on indefinitely
Virus can pop out of host cell’s chromosome at any time and enter LYTIC cycle

13. Disease symptoms explained by Lysogenic cycle
Cold sores
Herpes simplex 1
Remains even after cold sore healed
Cause of entering lytic cycle?
Chicken Pox
Shingles; nerve cells
HIV
Infect WBCs
Small packets of virus pinch off infected cell and go to other cells of immune system
Patient shows no syptoms until virus begins killing (lysis) the cells

14. HIV budding

15. RNA as Genetic Material
How can it insert itself into DNA?
Reverse transcriptase - enzyme coded for by virus
Makes DNA from RNA
DNA inserts into host chromosome
Then get lysogenic cycle

16. Where do Viruses come from?
First organisms? NO.
Viruses are more closely related to the cells they infect than to each other.
Viruses originate from host cells
Nucleic acids that escaped from host cell
Developed a way to reproduce as parasites of that same host

17. Vaccine Killed or damaged virus Injected into bloodstream
Cannot cause disease
Injected into bloodstream
Immune cells learn to recognize and fight any invader that looks like this virus
The REAL virus the vaccine is for
You don’t get sick from exposure to real virus later

18. Vaccine Edward Jenner Developed 1st Vaccine Small pox Deadly
Obtained pus from milkmaid suffering from cowpox
Cowpox – makes people sick, but is not deadly
Gave cowpox pus to a boy; he got cow pox
Exposed boy to small pox
Boy did not get small pox

19. Edward Jenner and Small Pox Vaccine

20. Why did it work?
Cow pox was similar enough to small pox that immune cells were able to recognize and fight BOTH cow pox AND small pox viruses after they had been exposed to cow pox.

21. Immunity given by Vaccines
LIFE LONG IMMUNITY as long as virus is stable and doesn’t MUTATE!
DNA viruses are MORE STABLE than RNA viruses
DNA viruses
Small pox
Has been eradicated
RNA viruses
HIV
Flu
Mutate often
Hard to develop vaccines; flu vaccine must be redeveloped each year.

22. Animation
Creation of a mutant virus and it’s spread – Click HERE