Chapter 20: Viruses and Prokaryotes

Section 20-2: Prokaryotes

Classifying Prokaryotes Unicellular organisms that lack a nucleus

DNA free-floating

Two groups domains: Bacteria and Archae

Bacteria Larger domain No agreement about number of phyla Live everywhere – fresh/salt water, land,

within other eukaryotes, etc Usually have a cell wall for shape and

protection – contains peptidoglycan Escherichia coli – found in human intestines –

have extra membrane around cell wall for more protection

Flagella for movement, pili to anchor bacterium

E. coli

Archae Look similar to Bacteria under a microscope

Cell walls contain lipids

DNA more like eukaryotes

Many live in harsh/extreme environments – salt lakes, hot springs, no oxygen, etc

Structure and Function Range in size from 1-5 micrometers Come in three shapes:

Bacillus (pl. bacilli) – rod shaped Coccus (pl. cocci) – spherical Spirillum (pl. spirilla) – spiral/corkscrew shaped

Also three arrangements: Diplo- (in a pair) Staphlyo (in a bunch) Strepto- (in a chain)

Shapes/Arrangements

Structure and Function Can be distinguished by how and if they move

– flagella, slime

Energy released during cellular respiration, fermentation, or both

Vary in the way they obtain energy

Growth, Reproduction, and Recombination Binary fission occurs when a prokaryote has

doubled in size – replicates its DNA and splits Asexual reproduction Can be very fast when conditions right

When conditions are unfavorable, many prokaryotes form endospores Thick wall forms around DNA and part of

cytoplasm Can stay dormant from many years Bacillus anthracis

Growth, Reproduction, and Recombination Mutations allow prokaryotes to evolve -

inherited through binary fission

Many prokaryotes also exchange genetic information through conjugation Hollow bridge forms between 2 bacterial cells and

genetic information (usually plasmids) move from one cell to another

Increases genetic diversity

Importance of Prokaryotes Decomposers – break down complex organic

molecules into simpler ones, supplying raw materials needed Actinomycetes in soil Sewage treatment Water purification Production of fertilizers

Producers – cyanobacteria responsible for photosynthesis in ponds/aquatic environments

Nitrogen fixers – convert atmospheric nitrogen gas into usable forms Symbiotic relationships with plants – Rhizobium and

legumes

Human Uses of Prokaryotes Foods/commercial products (yogurt produced

with Lactobacillus) Digest petroleum Remove human-made wastes and poisons

from water Synthesize drugs, chemicals by genetic

engineering Those adapted to extreme environments may

produce heat-stable enzymes