Chapter 28: Prokaryotes

Prokaryotes:

1) Domains Archaea and Bacteria
2) Oldest most abundant form of life
3) Essential
4) Create properties of atmosphere and soil (decomposers).
5) Industrial uses: vinegar, yogurt, cheese, bread, antibiotics
6) Used in mining, ammunition dumps, etc.

Cell Size: Most are 1 micrometer or less in diameter.

General Forms:

1) Bacilli- Rod shaped (bacillus singular)
2) Cocci- spherical (coccus singular)
3) Spirilla- spirally coiled (spirillum singular)
4) Vibrios- short, comma or S-shaped rods (vibrio singular)

Cyanobacteria: Group of photosynthetic bacteria that contain chlorophyll; formerly called blue-green algae, but are not algae, are bacteria.

Cell Interior:

A) Cytoplasm: relatively unstructured, does not have membrane around nucleus or organelles, no mitochondria (powerhouses of the cell). Nucleus instead named nucleoid region.

B) Have ribosomes- smaller and differ in structure than eukaryote cells.

C) Chromosomes in a circular DNA molecule.

D) Plasma membrane is made of different structures in archaebacteria and bacteria (one way to differentiate).

Cell Wall:

A) If the cell wall has a network of peptidoglycan (polysaccharide molecules connected by polypeptide cross links) bacteria is Gram-positive and retains crystal violet stain (purple colored bacteria after staining).

B) If the cell wall has a lipopolysaccharide (carbohydrate chain with lipids) covering the peptidoglycan, the dye will not adhere and it is Gram-negative bacteria.
-Gram Staining helps correlate sensitivity of bacteria to antibiotics.

Flagella and Pili:

A) Flagella made of protein flagellin
- 3-12 micrometers long
- 10-20 micrometers thick

B) Pili shorter than flagella
-Attach cells to substrate
-Also used in conjugation (reproduction).

Endospores:
-Thick wall around chromosome and small portion of cytoplasm.
-Resistant to environmental stress.
-Can revive decades or even centuries later.
-Examples: Tetanus, botulism, anthrax

Motility (Methods):

1) Flagella- rotary (spinning)
2) Gliding- mucous or slime excretion
3) Corkscrew- rotate

Reproduction:

1) Simple binary fission:
-Kingdom Bacteria has ribosomal proteins and RNA polymerase that are different from eukaryotes.
-Kingdom Archaebacteria are very similar to eukaryotes.

2) Two methods of variation:
a) Mutation: million copies in 7 hours (doubling time: 20 minutes)
b) Genetic Recombination: Transfer of genes, usually part of a virus or plasmid or other DNA fragment.

Metabolic Diversity:

1) Autotrophic: Obtain energy from sunlight or inorganic sources. Two types:
a) Photoautotrophic: photosynthetic; contains chlorophyll, but not plastids like plants.
b) Chemoautotrophic: derive energy from inorganic molecules (geothermic vent tube worms, bacteria inside them does this.)

2) Heterotrophic: mostly obtain energy form organic sources. Two types:
a) Photoheterotrophs: obtain energy from sunlight and carbon from other organisms.
b) Chemoheterotrophs: obtain energy and carbon by decomposition (like Rhizobium).
Called saprophytes: obtain enrichment from dead, organic matter.

Different Oxygen Requirements:

1) Aerobes: require oxygen
2) Obligate anaerobes: require no oxygen
3) Facultative anaerobes: can do with or without oxygen
(see page 555, important human bacterial diseases)