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Lesson Overview

Lesson Overview. 20.2 Prokaryotes. Classifying Prokaryotes. Prokaryotes are divided into two very distinct groups: Bacteria and Archaea.

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Lesson Overview

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  1. Lesson Overview 20.2 Prokaryotes

  2. Classifying Prokaryotes • Prokaryotes are divided into two very distinct groups: Bacteria and Archaea. • These groups are very different from each other; therefore, biologists now consider each group of prokaryotes as a separate domain. Eukaryotes are the third domain.

  3. Bacteria • The larger of the two domains of prokaryotes is the Bacteria. • Bacteria live almost everywhere— fresh water, salt water, on land, on and within bodies of humans and other eukaryotes. • Escherichia coli, a typical bacterium that lives in human intestines, is shown.

  4. Bacteria • Bacteria are usually surrounded by a cell wall. • Some bacteria, such as E. coli, have a second membrane outside the peptidoglycan wall that makes the cell especially resistant. • In addition, some prokaryotes have flagella that they use for movement, or pili, which in E. coli serve mainly to anchor the bacterium to a surface or to other bacteria.

  5. Archaea • Under a microscope, archaea look very similar to bacteria. Both are equally small, lack nuclei, and have cell walls, but there are important differences. • The walls of archaea lack peptidoglycan, and their membranes contain different lipids. • The DNA sequences of key archaea genes are more like those of eukaryotes than those of bacteria. • Based on these observations, scientists have concluded that archaea and eukaryotes are related more closely to each other than to bacteria.

  6. 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.

  7. 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. • bacterial communication

  8. Nutrition and Metabolism: Energy Capture

  9. Growth, Reproduction, and Recombination • Reproduction: binary fission asexual form of reproduction • When conditions are favorable, prokaryotes can grow and divide as often as once every 20 minutes! • When growth conditions become unfavorable, many prokaryotic cells form an endospore. • Endospores can remain dormant for months or even years. • The bacterium Bacillus anthracis, which causes the disease anthrax, is one such bacterium.

  10. Conjugation • conjugation: exchange genetic information • bridge forms between two bacterial cells, • genetic material, usually in the form of a plasmid, moves from one cell to the other. • This transfer of genetic information • increases genetic diversity • Many plasmids carry genes that enable bacteria to survive in new environments or to resist antibiotics that might otherwise prove fatal.

  11. Decomposers • Bacteria called actinomycetes are present in soil and in rotting plant material such as fallen logs, where they decompose complex organic molecules into simpler molecules. • Bacterial decomposers are also essential to industrial sewage treatment, helping to produce purified water and chemicals that can be used as fertilizers.

  12. Producers • Cyanobacteria in the genus Anabaena form filamentous chains in ponds and other aquatic environments, where they perform photosynthesis. • Photosynthetic prokaryotes are among the most important producers on the planet.

  13. 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.

  14. Human Uses of Prokaryotes • Prokaryotes, esp. bacteria, are used in the production of many foods and 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. • Some adapted to extreme environments may be a rich source of heat-stable enzymes that can be used in medicine, food production, and industrial chemistry.

  15. BIOREMEDIATION • Bioremediation: use biological organisms to solve an environmental problem • To clean up oil spills, bacteria are introduced to the area of the spill where they break down the hydrocarbons of the oil into carbon dioxide • Toxic metals, such as mercury , can be converted into nontoxic forms by bacteria

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