Bacteria & Archeae

Prokaryotes

Prokaryotes

• Single-celled microorganisms

• No nuclei, no membrane-bound organelles

• Circular DNA, reproduced by binary fission

• Single Haploid Chromosome (Sexual & Asexual Reproduction)

3 Major Prokaryotic Cell Shapes

1. Rods (bacillus/bacilli)

2. Speres (coccus/cocci)

3. Spiral (spirilla or spirochetes)

Bacillus/Bacilli

Rods

Coccus/Cocci

Spheres

Spirilla or spirochetes

Spiral

What is the purpose of a cell wall?

To protect & prevent cell lysis (rupture)

Bacteria Cell Weall

W/ peptidoglycan

Archaea Cell Wall

W/ other structural polysaccharides

What is a Gram stain?

A test used to identify bacteria.

What does a Gram stain reflect?

Cell wall type

Gram + (pos.)

Bacteria with thick Proteoglycan layer. Stains purple in Gram stain.

Gram - (neg.)

Bacteria with thinner Proteoglycan layer plus outer lipid bilayer membrane. Pink in Gram stain; outer lipopolysaccharide layer. Often toxic, resists drugs & immune system.

Capsule/Slime Layer

Sticky carbs & proteins secreted outside cell wall; adheres cells together or to surface. Resist attack from immune system. Holds in moisture.

Taxis

Movement directed toward or away from (+ or -) stimulus.

T or F: Rotating Flagellum protein fibers (found in prokaryotes) are homologous to eukaryote flagellum).

False

Some prokaryotes have in-folded plasma membranes…

for aerobic cellular respiration or for O2 producing photosynthesis.

Prokaryotic DNA

One chromosome: circular DNA molecule with binding proteins. Carries genes for all vital functions; much less DNA than eukaryotes.

Many Prokaryotes also have plasmids:

Extra tiny DNA rings w/ few genes. Replicate independently. Not “essential” for life, but add diversity (i.e. drug resistance genes).

Genetic diversity and metabolic/ecological diversity are…

mechanisms of diversity in prokaryotes!

How is Genetic Diversity created in Prokaryotes?

Via Recombination by Transformation, Transduction, & Conjugation.

How do prokaryotes divide?

By binary fission! Yield 2 identical cells (except for plasmids). Geometric growth in #’s.

What can limit prokaryotic growth?

Lack of food, moisture, crowding, etc. Under stress, some produce dormant cells.

High rate of cell division →

Many mutations

Genetic variation occurs by…

DNA mutations.

What is Recombination?

The process by which DNA strands are broken and repaired, producing new combinations of alleles.

Transformation

A form of genetic recombination in which a DNA fragment from a dead, degraded bacterium enters a competent recipient bacterium & is exchanged for a piece of DNA of the recipient.

What is Transduction?

A process of genetic recombination in which gene from a host cell (a bacterium) are incorporated into the genome of a bacterial virus (bacteriophage) & then carried to another host cell when the bacteriophage infect it.

What is Conjugation?

A form of sexual reproduction in bacteria.

How does Conjugation work?

Two individual cells are united by a tube formed by outgrowths from one or both cells. Genetic material from one cells (male) then passes through the tube to unite with the genetic material in the other cell (female).

F plasmid conjugation

Transfer of strand of F plasmid from F+ donor to F- recipient though mating bridge. F- cell becomes F+ cell (w/ F plasmid). R plasmid (genes for antibiotic resistance) can be transferred rapidly in this way.

Prokaryotes vary in their nutritional modes.

Some are autotrop (=photoautotroph or chemoautotroph) and some are heterotrop (photo- or chemoheterotroph).

Autotrophs are --- ---.

primary producers

P. fumarii

Example of a chemoautotroph. It produces its own energy from inorganic compounds in the geology and aqueous environment that it inhabits.

Facultative Anaerobes

Normally use O2 but switch to anaerobic processes if no O2 present

Obligate Aerobes

Require O2 for cellular respiration. Most life today.

What is the nitrogen cycle?

A cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems.

Metabolic Cooperation

Prokaryotes often growth better together.

Symbiosis

2 species living in close relationship

Free-living

Not living in symbiosis.

Parasitism

Smaller parasite benefits at expense of other species (host) including pathogens (cause disease).

Commensalism

One species benefits without any impact (good or bad) on the other species.

Mutualism

Both species benefit from each other.

T or F: Eukaryotes & Achaeans are more closely related to each other than either is to bacteria.

True

Example of Mutualistic Bacteria

Bacteria in the human digestive tract! Maintains normal colon function, ward off pathogenic bacteria, produce vitamins/other nutrients, and help activate immune system.

Endotoxins

Toxic outer membrane of some Gram-negative bacteria. Generalized toxic effect.

How to minimize/treat bacterial infection?

(1) Sanitation, (2) Immunization preps immune system to fight bacterial infections, and (3) Antibiotics kills bacteria cells but not eukaryotic cells.

Human Use of Prokaryotes

Basic research on cells & DNA; DNA technology & genetic engineering; commercial chemical & drug production. Food products: yogurt, cheese, kimchi, etc.

Methanogens

Produce methane (CH4) as a by-product of anaerobic respiration.