1. Virus Characteristics
2/28/19

2. Virus Characteristics
Viruses are considered nonliving particles because they cannot replicate on their own (THEY ARE NOT ALIVE)
They need a host cell – a cell that a virus uses to replicate
Viruses are very small particles
½ to 1/100 the size of a bacterial cell
Viruses do not perform cellular respiration, they do not grow, or develop
They infect bacteria cells, and the bacteria cells performs these functions for the virus

3. Virus size vs. Bacteria size
0.25 m
Virus
Animal cell
Bacterium
Animal cell nucleus

4. Virus Structure 2 main parts Capsid - outer coat of protein
Inner core made of nucleic acid (DNA or RNA)
This holds the instructions for making copies of the virus
Capsid - outer coat of protein
The capsid determines the shape of the virus
Polyhedral
Helical
envelope with projections
classic phage shape

5. (a) Tobacco mosaic virus
Virus Structures
18  250 mm
70–90 nm (diameter)
80–200 nm (diameter)
80  225 nm
20 nm
50 nm
(a) Tobacco mosaic virus
(b) Adenoviruses
(c) Influenza viruses
(d) Bacteriophage T4
RNA
Capsomere of capsid
DNA
Capsomere
Glycoprotein
Membranous envelope
Capsid
Head
Tail fiber
Tail sheath

6. A leaf infected by a tobacco mosaic virus

7. Bacteriophage

8. Adenovirus

9. Influenza virus

10. Viral Diseases Vaccines PREVENT viruses
Viruses are pathogenic and therefore disease causing.
Some viral diseases:
HIV
Influenza
Colds
Polio
Rabies
Smallpox
Hepatitis
Vaccines PREVENT viruses

11. Virus Specificity
Viruses are very specific as to which host cell that can infect
For example : HIV can only infect that Helper T Cells of humans
Their chemical recognizers (shape) coincides with the host cells receptors (shape)

12. Controlling Viruses
The bodies immune response to viruses is when white blood cells kill and remove viruses from the body.
Vaccines take advantage of this immune response
They are made of weakened or killed viruses which cause your body to have an immune response, but not make you sick
This builds up your immunity to a virus
Once your body fights off a virus, your Helper T Cells remember that virus and it can never make you sick again
This is why you have to get a flu shot every year
The virus mutates and your Helper T cells don’t recognize it