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VIRUSES. Virus. A particle composed of nucleic acid, protein, and in some cases lipids that can reproduce only by infecting living cells. The term, virus, comes from the Latin word for poison. Most viruses are highly specific to the cells they infect. Structure of Viruses.

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  • A particle composed of nucleic acid, protein, and in some cases lipids that can reproduce only by infecting living cells.

  • The term, virus, comes from the Latin word for poison.

  • Most viruses are highly specific to the cells they infect.

Structure of viruses

Structure of Viruses

  • Envelope—membrane surrounding the capsid

  • Capsid— virus’s outer protein coat

  • Core—DNA or RNA located inside the capsid

Bacteriophage a virus that infects bacteria

Bacteriophage—a virus that infects bacteria

Types of viral infection

Types of viral infection:

  • Lytic infection—virus actively uses the host cell to make

  • copies of itself, destroying the host cell in the process.

  • Lysogenic infection—virus embeds its DNA into the host

  • cell DNA and is replicated along with the host cells DNA.

  • It does not destroy the host cell immediately. Viral DNA

  • embedded in the host DNA is called a prophage.

  • Eventually something will trigger the viral DNA to remove

  • itself from the host cell DNA and direct the synthesis of

  • new viruses.

Vaccine best way to protect against viral infections

Vaccine—best way to protect against viral infections.


Retroviruses—contain RNA as their genetic information. Get their name from the fact that the genetic information is copied backwards. HIV (human immunodeficiency virus) is a retrovirus.


Prions—contain no DNA, just protein. Prion means, “protein infectious particles”. Diseases such as mad cow disease (cows), scrapie (sheep and goats), and kuru (humans) may be caused by these.





  • Prokaryotic

  • Unicellular

  • Some photosynthetic species, some chemosynthetic species, some heterotrophic species.

Grouped according to shape

Grouped according to shape

  • Coccus—spherical

  • Bacillus—rod shaped

  • Spirillum—spiral

Prefixes indicate how they group

Prefixes indicate how they group



Kingdom archaebacteria

Kingdom Archaebacteria

  • Prokaryotes that live in harsh environments such as hot springs, the great salt lake and dead sea, intestines of cattle, under sediment in marshes, and deep ocean vents.

  • The name literally means “ ancient bacteria”.

  • Most, if not all, are chemoautotrophs.

Types of archaebacteria

Types of archaebacteria

Methanogens—produce methane gas in oxygen free environments. Found in marshes, lake sediments, and in the digestive tracts of some mammals, such as cows.

Extreme halophiles—live in water with high salt concentrations.

Thermoacidophiles—live in extremely hot water such as hot springs and deep ocean vents.

Kingdom eubacteria

Kingdom Eubacteria

  • Most of the common bacteria that we come into contact with every day are eubacteria.

  • Eubacteria literally means “true bacteria”.

  • Most, if not all, disease causing bacteria are eubacteria.

  • Cyanobacteria are a type of photosynthetic eubacteria.

Cyanobacteri a


  • Have some traits similar to plants and plantlike protists.

  • All are autotrophic.

  • Many encased in a jelly-like substance.

How bacteria acquire nutrition

How bacteria acquire nutrition

  • Most are heterotrophs.

  • Some are saprophytes (heterotrophs) that feed on dead or decaying matter.

  • Many are autotrophs—may be either photoautotrophs (cyanobacteria) or chemoautotrophs (nitrogen fixing bacteria).

Structure of bacteria

Structure of bacteria

  • Nucleoid—bacterial DNA found in a single clustered chromosome.

  • Plasmids—circular strands of DNA found in many bacteria.

  • Capsules—protective layers of polysaccharides around the cell wall found in many bacteria.

Structure of bacteria1

Structure of bacteria

  • Pili—protein strands many bacteria use to attach themselves to things.

  • Flagella—found on some for movement.

  • Endospore—contains a bacterium’s DNA and a small amount of its cytoplasm. Helps a bacterium survive harsh conditions.

Eubacteria may be classified according to how they use oxygen

Eubacteria may be classified according to how they use oxygen.

  • Obligate anaerobes—cannot survive in the presence of oxygen

  • Facultative anaerobes—can live with or without oxygen

  • Obligate aerobes—must have oxygen

Bacterial reproduction

Bacterial reproduction

Binary fission—asexual splitting in two (some may divide every 15 minutes)

Bacterial reproduction1

Bacterial reproduction

Conjugation—sexual recombination of DNA



  • Disease causing viruses, bacteria, or other organisms.

  • Many produce toxins.

  • Antibiotics fight bacteria but not viruses.

Importance of bacteria

Importance of bacteria

  • Nitrogen fixation—conversion of atmospheric nitrogen into ammonia by some bacteria found on the roots of legumes

  • Recycling of nutrients

  • Food made using bacteria include cheese, pickles, yogurt, buttermilk, wine vinegar, and sauerkraut

  • Many antibiotics are made from bacteria

  • Disposal of toxic or harmful chemicals (cobalt, uranium, zinc, cyanide, dioxin, PCB’s, agent orange)

  • Genetically engineered bacteria produce drugs such as insulin

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