1. Viruses, Bacteria, and Archaea
Chapter 21
Mader: Biology 8th Ed.

2. Outline Viruses Structure Classification Reproduction Prokaryotes
Nutrition
Bacteria
Archaea
Mader: Biology 8th Ed.

3. Generally smaller than 200 nm in diameter.
The Viruses
Viruses are noncellular and thus cannot be classified with cellular organisms.
Generally smaller than 200 nm in diameter.
Each type has at least two parts.
Capsid: Outer layer composed of protein subunits.
Nucleic acid core: DNA or RNA.
Mader: Biology 8th Ed.

4. The Viruses
Mader: Biology 8th Ed.

5. Classification is based on: Type of nucleic acid. Size and shape.
The Viruses
Classification is based on:
Type of nucleic acid.
Size and shape.
Presence / absence of outer envelope.
Mader: Biology 8th Ed.

6. The Viruses
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7. Can infect a wide variety of cells, but are very specific.
Parasitic Nature
Viruses are obligate inrtracellular parasites (cannot reproduce outside a living cell).
Can infect a wide variety of cells, but are very specific.
Bacteriophages - Infect bacterial cells.
Mader: Biology 8th Ed.

8. Virus takes over metabolic machinery of the host cell.
Viral Reproduction
Viruses gain entry into host because portions of capsid adhere to a specific receptor on the host cell’s outer surface.
Viral nucleic acid enters the cell and once inside, the nucleic acid codes for the protein units inside the capsid.
Virus takes over metabolic machinery of the host cell.
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9. Lytic cycle may be divided into five stages: Attachment Penetration
Biosynthesis
Maturation
Release
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10. Phage becomes a prophage that is integrated into the host genome.
Lysogenic Cycle
Phage becomes a prophage that is integrated into the host genome.
Becomes latent, and later may reenter the lytic cycle.
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11. Reproduction of Animal Viruses
After animal viruses enter the host cell, uncoating releases viral DNA or RNA and reproduction occurs.
If viral release occurs by budding, the viral particle acquires a membranous envelope.
Retroviruses
Contain reverse transcriptase which carries out RNA  cDNA transcription.
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12. Reproduction of HIV-1
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13. Viral Infections
Viruses are best known for causing infectious diseases in plants and animals.
Herpes, HIV, cancer
Viruses lack enzymes; thus, antibiotics have no effect.
Many crop diseases have been attributed to viroids (naked strands of RNA).
Some human and other animal diseases have been attributed to prions (protein molecules).
Mad cow disease
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14. A single spoonful of earth can contain 1010 prokaryotes.
The Prokaryotes
The prokaryotes include bacteria and archaea, which are fully functioning cells.
A single spoonful of earth can contain 1010 prokaryotes.
Range in size from 1-10µm in length and µm in width.
Mader: Biology 8th Ed.

15. Lack a eukaryotic nucleus.
Prokaryote Structure
Lack a eukaryotic nucleus.
Have outer cell wall containing peptidoglycan.
Some move by means of flagella.
Lack membranous organelles.
Contain nucleoid.
May have accessory ring of DNA (plasmid).
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16. Flagella
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17. Reproduction in Prokaryotes
Prokaryotes reproduce asexually by means of binary fission.
Conjugation occurs between bacteria when the donor cell passes DNA to recipient cell by way of sex pilus.
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18. Binary Fission
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19. Reproduction in Prokaryotes
Transformation occurs when bacterium picks up free pieces of DNA from other prokaryotes.
Transduction occurs when bacteriophages carry portions of bacterial DNA from one cell to another.
When faced with unfavorable conditions, some bacteria form endospores.
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20. Prokaryotic Nutrition
Obligate anaerobes are unable to grow in the presence of free oxygen.
Facultative anaerobes are able to grow in either the presence or absence of gaseous oxygen.
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21. Autotrophic Prokaryotes
Photoautotrophs use solar energy to reduce carbon dioxide to organic compounds.
Photosynthetic
Chemoautotrophs oxidize inorganic compounds to obtain the necessary energy to reduce O2 to an organic compound.
Chemosynthetic
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22. Heterotrophic Prokaryotes
Most prokaryotes are chemotrophs that take in organic nutrients.
Aerobic saprotrophs decompose most large organic molecules to smaller molecules.
May be free-living or symbiotic.
Nitrogen fixation
Commensalism
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23. Gram-positive bacteria retain dye and appear purple.
The Bacteria
Groups of bacteria are commonly differentiated from one another using the Gram stain procedure.
Gram-positive bacteria retain dye and appear purple.
Gram-negative bacteria do not retain dye and appear pink.
Mader: Biology 8th Ed.

24. Bacteria can also be classified in terms of their three basic shapes.
The Bacteria
Bacteria can also be classified in terms of their three basic shapes.
Spiral (spirilli), Rod (bacilli), and Round (cocci).
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25. Cyanobacteria are Gram-negative bacteria that photosynthesize.
Believed to be responsible for introducing oxygen into the primitive atmosphere.
Lack visible means of locomotion.
Can live in extreme environments.
In association with fungi, form lichens.
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26. Cyanobacteria
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27. The Archaea
Archaea were considered bacteria until Carl Woese discovered their rRNA has a different sequence of bases than rRNA of bacteria.
Eukarya are believed to be more closely related to archaea than to bacteria.
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28. Archaea Structure and Function
Plasma membranes of archaea contain unusual lipids that allow them to function at high temperatures.
Some are methanogenic.
Most are chemoautotrophs.
None are photosynthetic.
Sometimes mutualistic or commensalistic, but none are parasitic.
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29. Found in anaerobic environments.
Types of Archaea
Methanogens
Found in anaerobic environments.
Produce methane from hydrogen gas and carbon dioxide.
Halophiles
Require high salt concentrations for growth.
Thermoacidophiles
Reduce sulfides and survive best at temperatures above 80oC.
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30. Review Viruses Structure Classification Reproduction Prokaryotes
Nutrition
Bacteria
Archaea
Mader: Biology 8th Ed.

31. Mader: Biology 8th Ed.