Viruses and Monera Jessica Jones Spring 2007

What do these diseases have in common? Measles Mumps re/IMAGE/MUMPS.GIF Polio essionals/Diseases/Polio/Polio.jpg Hepatitis B

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.

Structure of a Virus /hdc_0001_0001_0_img0008.jpg DNA (or RNA) Protein capsid Tube Tail Fiber

 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. gene/sf11x1virus.jpg

No, they aren’t from the 70’s.  Retroviruses  These are viruses that store their genetic information as RNA.  Example: HIV

How it works……

Kingdom Monera…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 roc_shapes.jpg

Structure of a Bacteria Cell membrane Cell wall Ribosomes DNA

 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).

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.

We’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.  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.

 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.

 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