1. Lesson Overview Lesson OverviewViruses Lesson Overview 20.2 Prokaryotes

2. Lesson Overview Lesson OverviewViruses Bio Announcements Bacteria and Viruses Quiz and Assessment 25 multiple choice question

3. Lesson Overview Lesson OverviewViruses Classifying Prokaryotes How are prokaryotes classified? Prokaryotes are classified as Bacteria or Archaea—two of the three domains of life.

4. Lesson Overview Lesson OverviewViruses Classifying Prokaryotes The smallest and most abundant microorganisms on Earth are prokaryotes—unicellular organisms that lack a nucleus. Prokaryotes have DNA, like all other cells, but their DNA is not found in a membrane-bound nuclear envelope as it is in eukaryotes. Prokaryote DNA is located in the cytoplasm. A bacterium such as E. coli has the basic structure typical of most prokaryotes.

5. Lesson Overview Lesson OverviewViruses Bacteria Bacteria live almost everywhere—in fresh water, in salt water, on land, and on and within the bodies of humans and other eukaryotes. Escherichia coli, a typical bacterium that lives in human intestines, is shown.

6. Lesson Overview Lesson OverviewViruses Bacteria Bacteria are usually surrounded by a cell wall that protects the cell from injury and determines its shape. The cell walls of bacteria contain peptidoglycan—a polymer of sugars and amino acids that surrounds the cell membrane. Some bacteria, such as E. coli, have a second membrane outside the peptidoglycan wall that makes the cell especially resistant to damage.

7. Lesson Overview Lesson OverviewViruses Archaea Many archaea live in extremely harsh environments. One group of archaea produce methane gas and live in environments with little or no oxygen, such as thick mud and the digestive tracts of animals. Other archaea live in extremely salty environments, such as Utah’s Great Salt Lake, or in hot springs where temperatures approach the boiling point of water.

8. Lesson Overview Lesson OverviewViruses Structure and Function How do prokaryotes vary in their structure and function? Prokaryotes vary in their size and shape, in the way they move, and in the way they obtain and release energy.

9. Lesson Overview Lesson OverviewViruses Size, Shape, and Movement Prokaryotes range in size from 1 to 5 micrometers, making them much smaller than most eukaryotic cells. Prokaryotes come in a variety of shapes. Rod-shaped prokaryotes are called bacilli. Spherical prokaryotes are called cocci. Spiral and corkscrew-shaped prokaryotes are called spirilla.

10. Lesson Overview Lesson OverviewViruses Nutrition and Metabolism: Energy Capture

11. Lesson Overview Lesson OverviewViruses Nutrition and Metabolism: Energy Release

12. Lesson Overview Lesson OverviewViruses Growth, Reproduction, and Recombination When a prokaryote has grown so that it has nearly doubled in size, it replicates its DNA and divides in half, producing two identical cells. This type of reproduction is known as binary fission.

13. Lesson Overview Lesson OverviewViruses Growth, Reproduction, and Recombination Because binary fission does not involve the exchange or recombination of genetic information, it is an asexual form of reproduction. When conditions are favorable, prokaryotes can grow and divide at astonishing rates— some as often as once every 20 minutes!

14. Lesson Overview Lesson OverviewViruses Growth, Reproduction, and Recombination When growth conditions become unfavorable, many prokaryotic cells form an endospore—a thick internal wall that encloses the DNA and a portion of the cytoplasm. Endospores can remain dormant for months or even years.

15. Lesson Overview Lesson OverviewViruses Growth, Reproduction, and Recombination The ability to form endospores makes it possible for some prokaryotes to survive very harsh conditions. The bacterium Bacillus anthracis, which causes the disease anthrax, is one such bacterium.

16. Lesson Overview Lesson OverviewViruses Conjugation Many prokaryotes exchange genetic information by a process called conjugation. During conjugation, a hollow bridge forms between two bacterial cells, and genetic material, usually in the form of a plasmid, moves from one cell to the other.

17. Lesson Overview Lesson OverviewViruses Conjugation Many plasmids carry genes that enable bacteria to survive in new environments or to resist antibiotics that might otherwise prove fatal. This transfer of genetic information increases genetic diversity in populations of prokaryotes.

18. Lesson Overview Lesson OverviewViruses The Importance of Prokaryotes What roles do prokaryotes play in the living world? Prokaryotes are essential in maintaining every aspect of the ecological balance of the living world. In addition, some species have specific uses in human industry.

19. Lesson Overview Lesson OverviewViruses Decomposers By decomposing dead organisms, prokaryotes, supply raw materials and thus help to maintain equilibrium in the environment. Bacterial decomposers are also essential to industrial sewage treatment, helping to produce purified water and chemicals that can be used as fertilizers.

20. Lesson Overview Lesson OverviewViruses Producers Cyanobacteria in the genus Anabaena form filamentous chains in ponds and other aquatic environments, where they perform photosynthesis.

21. Lesson Overview Lesson OverviewViruses Producers Photosynthetic prokaryotes are among the most important producers on the planet. Food chains everywhere are dependent upon prokaryotes as producers of food and biomass.

22. Lesson Overview Lesson OverviewViruses Nitrogen Fixers All organisms need nitrogen to make proteins and other molecules. Nitrogen gas (N 2 ) makes up 80 percent of Earth’s atmosphere, but only a few kinds of organisms—all of them prokaryotes—can convert N 2 into useful forms. The process of nitrogen fixation converts nitrogen gas into ammonia (NH 3 ). Ammonia can then be converted to nitrates that plants use, or attached to amino acids that all organisms use. Nitrogen-fixing bacteria and archaea provide 90 percent of the nitrogen used by other organisms.

23. Lesson Overview Lesson OverviewViruses Nitrogen Fixers Some plants have symbiotic relationships with nitrogen-fixing prokaryotes. The bacterium Rhizobium grows in nodules, or knobs, on the roots of legume plants such as soybean. The Rhizobium bacteria within these nodules convert nitrogen in the air into the nitrogen compounds essential for plant growth.

24. Lesson Overview Lesson OverviewViruses Nitrogen Fixers The Rhizobium bacteria often live symbiotically within nodules attached to roots of legumes, such as clover, where they convert atmospheric nitrogen into a form that is useable by plants.

25. Lesson Overview Lesson OverviewViruses Human Uses of Prokaryotes Prokaryotes, especially bacteria, are used in the production of a wide variety of foods and other commercial products. Yogurt is produced by the bacterium Lactobacillus. Some bacteria can digest petroleum and remove human-made waste products and poisons from water. Other bacteria are used to synthesize drugs and chemicals through the techniques of genetic engineering. Bacteria and archaea adapted to extreme environments may be a rich source of heat-stable enzymes that can be used in medicine, food production, and industrial chemistry.

26. Lesson Overview Lesson OverviewViruses Bacteria and Virus Project Select two diseases: one caused by a virus and the other by a bacteria Prepare a poster to present to the class Include the following headings: 1.Name of the disease 2.Cause of the disease, state whether it is infectious, contagious or both 3.Incubation period and who the disease affects 4.Symptoms 5.Mode of transmission 6.Incubation 7.Prevention and treatment