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Viruses and Bacteria

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What do these diseases have in common?

Measles http://www.idph.state.il.us/images/measles.jpg

Mumps http://www.kcom.edu/faculty/chamberlain/Website/lectures/lecture/IMAGE/MUMPS.GIF

Polio http://www.immune.org.nz/site_resources/Professionals/Diseases/Polio/Polio.jpg

Hepatitis B http://www.idph.state.il.us/images/hepatitisb.jpg

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It looks alive, acts alive… but its not!

• Viruses are not living things. They differ from living things in several ways:– They need to be inside a living organism to

reproduce themselves.– Outside the cell, they have no metabolism.– They do not have cell parts. (i.e. nucleus,

mitochondria, etc)– They are composed of only a nucleic acid

(DNA or RNA) inside a protein capsule.

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• Viral Reproduction– In order to reproduce:

• A virus attaches to a host cell.• The virus injects the cell with its nucleic acid.• The viral nucleic acid commands the cell to make more

viral protein and nucleic acid.• The cell then ruptures, releasing hundreds of new

viruses.

http://porpax.bio.miami.edu/~cmallery/150/gene/sf11x1virus.jpg

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Retroviruses…No, they aren’t from the 70’s!

– These are viruses that store their genetic information as RNA.

– Their genetic information is copied backward-from DNA to RNA.

• Ex: some types of cancer & AIDS

http://international.ucla.edu/cms/images/hiv_virus.jpg

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How it works……

• They infect their host cell.

• They produce a DNA copy of their RNA.

• It may remain dormant for varying lengths of time.

http://hiv.buffalo.edu/./images/hiv_virus_in_action.jpg

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Your friendly bacteria

• Bacteria are living, unicellular prokaryotes.• Divided into two kingdoms: Eubacteria and

Archaebacteria• Heterotroph or autotroph (most use

chemosynthesis).• Types of Bacteria are classified based on

their shape, type of cell wall, and movement.

• Bacteria have three basic shapes:– Bacilli – rod-shaped– Cocci – spherical– Spirilla – spiral

http://fig.cox.miami.edu/~cmallery/150/proceuc/c27x3proc_shapes.jpg

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• Eubacteria have peptidoglycan and certain specialized lipids in their cells walls that are not present in Archaebacteria.

• Gram staining is used to differentiate types of Eubacteria. – Those having thick cell walls will absorb more of the

dye and appear dark purple (Gram positive).– Those having thinner cell walls will absorb less of

the dye and appear pink (Gram negative).

http://bioweb.uwlax.edu/bio203/s2008/jaedike_alic/grainpositive.jpg http://www.asm.org/Division/c/photo/gc1.JPG

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Bacteria Growth and Reproduction

• Bacteria reproduce in two main ways:– Binary fission – when a bacteria grows

to double its original size, it copies its DNA and divides, producing two identical cells.

– Conjugation – a hollow bridge is formed between 2 bacteria and genes are transferred from one cell to the other.

• This creates genetic diversity within the population.

– Spore formation – when conditions are unfavorable (lack of food, drought) that encloses its DNA and part of its cytoplasm in a spore.

• When conditions are better, the spore will germinate, and the bacterium will continue to grow.

http://porpax.bio.miami.edu/~cmallery/150/gene/sf9x3box.jpg

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/69091a.jpg

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They’re not all bad….

• Bacteria are most widely known for causing diseases such as strep throat, tetanus, meningitis, and tuberculosis.

• However, most bacteria are very useful:– E. coli helps us digest our food & make vitamins for

humans.– Many are important decomposers in our ecosystem.– Rhizobium provides plants with nitrogen.– A few bacteria are used to clean up small oil spills in

the ocean.

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• Vaccinations– A weakened form of the pathogen

(virus/bacteria) is used to stimulate the production of antibodies.

– However, bacteria and viruses have very high reproductive rates, which result in many mutations.

– Thus, bacteria and viruses evolve quickly, often requiring a different vaccine every year.

http://www.biojobblog.com/vaccination(5).jpg

http://www.biojobblog.com/vaccination%5B1%5D.JPG

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• There are two types of vaccines (immunities):

• Active – person is injected with the actual pathogen, and immune cells make their own antibodies against the disease, immunity is permanent

• Passive – person is injected with antibodies that fight the disease, but immunity is temporary

http://www.iavi.org/viewpage.cfm?aid=1682