1. Topic 2.2 Prokaryotes
By Laura Sugden

2. What are Prokaryotes? (see chapter 27)
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.

3. Domain Bacteria Domain Archaea Eukarya
Alpha
Beta
Gamma
Epsilon
Delta
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Gram-positive
bacteria
Korarchaeotes
Euryarchaeotes
Crenarchaeotes
Nanoarchaeotes
Eukaryotes
Universal ancestor

4. Prokaryote Characteristics
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 µm for the eukaryotes.
However there is an exception to the rule…

5. 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!

6. Examples of Diversity of Prokaryotes

7. Cell-Surface Structures
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.

8. 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

9. 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
Capsule
Figure 27.4

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

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

12. (a) Aerobic prokaryote (b) Photosynthetic prokaryote
Other Structures?
Some prokaryotes do have specialized membranes that perform metabolic functions
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
0.2 m
1 m
Respiratory
membrane
Thylakoid
membranes
Figure 27.7a, b

13. 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
Figure 27.8
1 m
Chromosome

14. Some bacteria also have small circular pieces of DNA called plasmids…we will work with them soon!

15. Prokaryotes have a 70S ribosome

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

17. Transformation, Conjugation & Transduction
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!

18. Endospores
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.