Lesson Overview 20.2 Prokaryotes

THINK ABOUT IT When the microscope was first invented, we humans had just such a shock. Far from being alone, we share every corner of our world with microorganisms. Even a seemingly clean toothbrush contains a film of bacteria on its bristles!

Classifying Prokaryotes The smallest & most abundant microorganisms on Earth are prokaryotes unicellular organisms lack a nucleus. Prokaryotes have DNA, like all other cells, DNA is not found in a membrane-bound nuclear envelope Ex.) E Coli

Classifying Prokaryotes Prokaryote DNA is located in the cytoplasm. A bacterium such as E. coli has the basic structure typical of most prokaryotes.

Classifying Prokaryotes Biologists divided prokaryotes into 2 distinct groups: Bacteria Archaea These groups are very different from each other; biologists now consider these group of prokaryotes as a separate domain. Eukaryotes are the third domain. (have a nucleus)

Bacteria The larger of the two domains of prokaryotes is the Bacteria. Bacteria include a wide range of organisms * lifestyles = different that biologists do not agree exactly how many phyla are needed to classify this group.

Bacteria Habitat: 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.

Bacteria Bacteria 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.

Bacteria Some bacteria, such as E. coli, have a second membrane outside the peptidoglycan wall that makes the cell especially resistant to damage.

Bacteria 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.

Archaea Under a microscope, archaea look very similar to bacteria. 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.

Archaea Many archaea live in extremely harsh environments. One group of archaea produce methane gas and live in environments with little or no oxygen, thick mud digestive tracts of animals. Other archaea live in extremely salty environments Utah’s Great Salt Lake hot springs

Size, Shape, and Movement Size from 1 to 5 micrometers (much smaller than most eukaryotic cells.) Shapes Rod-shaped-bacilli. Spherical-cocci. Spiral and corkscrew-shaped-spirilla.

Size, Shape, and Movement Prokaryotes can also be classified by whether they move and how they move. Some prokaryotes do not move at all. Others are propelled by flagella. Some glide slowly along a layer of slimelike material

Nutrition and Metabolism Prokaryotes need a supply of chemical energy, which they store in the form of fuel molecules -sugars. Energy is released from these fuel molecules during cellular respiration, fermentation, or both.

Nutrition and Metabolism Prokaryotes vary in the ways they obtain energy and the ways they release it. Looking at the two tables on the following slides, notice that some species are able to change their method of energy capture or release depending on the conditions of their environment.

Nutrition and Metabolism: Energy Capture

Nutrition and Metabolism: Energy Release

Growth, Reproduction, and Recombination binary fission-when growth of a prokaryote doubled in size, it replicates its DNA and divides in half, producing two identical cells.

Growth, Reproduction, and Recombination Binary fission does not involve the exchange or recombination of genetic information asexual reproduction-no genetic exchange When conditions are favorable, prokaryotes can grow and divide at astonishing rates—some as often as once every 20 minutes!

Growth, Reproduction, and Recombination When growth conditions are unfavorable prokaryotes 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.

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.

Mutation Mutations are changes in DNA that occur in organisms. Mutations are one of the main ways prokaryotes evolve Inherited by daughter cells produced by binary fission.

Conjugation Conjugation is an exchange of genetic information in bacteria During conjugation, a hollow bridge forms between two bacterial cells genetic material, plasmid, moves from one cell to the other.

Conjugation Many plasmids carry genes that enable bacteria to survive in new environments or to resist antibiotics that might otherwise prove fatal. This type of reproduction increases genetic diversity

Decomposers Bacteria called actinomycetes are found in soil & rotting plant material such as fallen logs, they decompose complex organic molecules into simpler molecules.

Decomposers By decomposing dead organisms bacteria help to maintain equilibrium in the environment. Bacterial decomposers are also essential to sewage treatment produce purified water and chemicals used as fertilizers.

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

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.

Nitrogen Fixers Organisms need nitrogen to make proteins and other molecules. Some prokaryotes—can convert N2 into useful forms. The process of nitrogen fixation converts nitrogen gas into ammonia (NH3). Ammonia can then be converted to nitrates that plants use, or attached to amino acids that all organisms use.

Nitrogen Fixers Nitrogen-fixing bacteria & archaea provide 90 percent of the nitrogen 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.

Nitrogen Fixers The Rhizobium bacteria within these nodules convert nitrogen in the air into the nitrogen compounds essential for plant growth. 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.

Human Uses of Prokaryotes Prokaryotes are used in the production of foods & commercial products. Yogurt is produced by the bacterium Lactobacillus. Some bacteria can digest petroleum and remove human-made waste products and poisons from water.

Human Uses of Prokaryotes Other bacteria are used to synthesize drugs & chemicals through the techniques of genetic engineering. Bacteria and archaea adapted to extreme environments may be a rich source of heat-stable enzymes can be used in medicine food production industrial chemistry.