4.2 Prokaryota

1. Structural and functional adaptations

0.5-5 µm in diameter Shape:

Sphere (cocci) Rod (bacilli) Spiral

2. Cell surface structures

Cell wall of bacteria Cell wall of archaea Peptidoglycan (matrix composed

of modified sugar polymers cross-linked by short polypeptides)

Provides physical protection & prevents cell from bursting in hypotonic environment

No peptidoglycan but can be gram+/ -

Contain variety of polysaccharides & proteins

Gram + Gram - Simpler Thick layer of peptidoglycan

(protein+carbohydrate) No lipopolysaccharide

(lipid+carbohydrate) membrane

Complex Less peptidoglycan

Have an outer lipoplysaccharide membrane

Sticky capsule outside cell wall Protection from host’s immune system Glue for adhering to substrate

Attach by hairlike appendages frimbae – shorter & more numerous than sex pilli Sex pilli – specialized for exchange of DNA between prokaryotes

3. Motility

Flagella Scattered over cell surface/ concentrated at one or both ends of cells Lack of plasma membrane over Different from eukaryotic flagella Naked protein structure that lacks microtubules

Exhibit taxis (respond to chemical/light/other stimuli)

4. Internal and genomic organization

Lack of complex compartmentalization

Some have specialized membranes that perform metabolic functions Infoldings of plasma membrane – respiration &photosynthesis

Less DNA than eukaryotes Genome consists of circular chromosomes with fewer proteins Chromosome located in nucleoid Plasmids – smaller rings of DNA which only carry a few genes Ribosomes – smaller than eukaryotes & differ in protein and RNA content Some antibiotics – bind to ribosomes & block protein synthesis of prokaryotes

5. Reproduction & Adaptation

Reproduce quickly in favorable environment Small Reproduce by binary fission Short generation times – 20 mins to 3 hours Reproduction limited by:

No nutrients Too much waste products

Form protective structures – endospores when lack of essential nutrients Contains genetic material & a few enzymes encased within thick protective

coat Water is removed from endospores Cell breaks – endospores released Metabolic activity ceases until spore encounters favorable condition Resistant to extreme environmental conditions

Genetic recombination Transformation

Transduction

Conjugation Bacterial cell temporarily join to another cell by sex pilli Donor transfer DNA to recipient through “mating bridge” between two

cells Ability to form pilli and donate DNA results from presence of F factor

(F for fertility) F factor can exist as plasmid/segment of DNA within bacterial

chromosome Cells containing F factor are designated F+ cells ; lack F factor,

designated F-

6. Nutritional modes

Autotrophs – obtain carbon from carbon dioxide Heterotrophs – obtain carbon from organic compounds of other organisms

Archaea

Usually are extremophiles Extreme halophiles

live in highly saline environments tolerate salinity

Extreme thermophiles Thrive in very hot environment

Methanogens Live in anaerobic environment & give off energy and methane waste Live in swamps & marshes Decomposers in sewage treatment

Bacteria

Proteobacteria Gram – Share a particular rRNA sequence Have high metabolic diversity

Chlamydias Live inside eukaryotic host cells Parasites

Spirochetes Helical bacteria moving in corkscrew fashion

Gram + Diverse group

Cyanobacteria Plantlike Oxygen-generating photosynthesis Provide enormous amount of food for freshwater and marine ecosystems Many have symbiotic relationships with organisms such as fungi, mosses and

marine invertebrates