By Laura Sugden

• Traditional Classification-Monera (one of the 5 kingdoms…can you name the others?)
• Modern Classification breaks Monera into two groups ( two of the 6 Kingdom classification system) the Eubacteria (or often just called bacteria) and the Archaebacteria.
• Now we favor a 3 domain system (domain would lie above the kingdom level) including bacteria, archeabacteria and eukarya the eukaryotic kingdoms.
• These differences were determined by genome comparison and ribosomal RNA sequences.

Proteobacteria
Domain Bacteria
Domain
Archaea
Domain
Eukarya
Universal ancestor

• Most are unicellular, but some aggregate in groups
• Shape differences
Sperical (cocci) Rod (bacilli) Helical
• Size ranges from 1-5 µm for most prokayotes compared to 10-
100 µm for the eukaryotes.
• However there is an exception to the rule…

• The largest prokaryote on earth was discovered not before
1997, although the cells are visible with the naked eye.
Thiomargarita namibiensis, which means 'sulfur pearl from
Namibia', inhabits the sediments along the west coast of Africa
• This speicies is roughly 750µm in size!

• One of the most important features of nearly all prokaryotic cells is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment
• The cell wall does not contain cellulose like plant cells but a unique material called peptidoglycan, a carb composed of sugars cross linked with short polypeptides.
• The effecxt is a closed and protective network.
• Peptidoglycan distribution has species variations.

Cell-Surface Structures
Using a technique called the Gram stain
, scientists can classify many bacterial species into two groups based on cell wall composition, Gram-positive and Gram-negative

Surface Cell Structures
• The cell wall of many prokaryotes is covered by a capsule, a sticky layer of polysaccharide or protein
• This allows the bacteria to adhere to things and provides additional protection.
• The capsule is also important to those bacteria that live as colonies.
200 nm
Figure 27.4
Capsule

Cell-Surface Structures
• Some prokaryotes have fimbriae and pili, which allow them to stick to their substrate or other individuals in a colony
Figure 27.5
200 nm
Fimbriae

• Most motile bacteria propel themselves by flagella, which are structurally and functionally different from eukaryotic flagella

• Some prokaryotes do have specialized membranes that perform metabolic functions
0.2 m 1 m
Respiratory membrane
Figure 27.7a, b (a) Aerobic prokaryote
Thylakoid membranes
(b) Photosynthetic prokaryote

The Nucleoid Region
• The typical prokaryotic genome is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region
Chromosome
Figure 27.8
1 m

• Asexual BINARY FISSION…every 1-3 hours. Binary fission is different from mitosis or meiosis. Click here for animation.

• Transformation occurs when prokaryotes take up genes from the surrounding environment allowing for genetic transfer…even between species lines!
• Conjugation is as close to sexual reproduction as prokaryotes get. The transfer genes from one cell to the other.
• Transduction occurs when viruses transfer genes between prokaryotes when a cell has become infected with a bacteriophage (virus).
• Mutation is the major source of genetic variation…mutation and rapid growth!

• Some bacteria have the ability to develop endospores by replicating its chromosome and forming a durable wall around it.
• The outer cell dissolves and leaves a highly durable endospore.
• These can withstand extremely high heat and very harsh conditions allowing them to even survive centuries in a dormant state.