1. Prokaryotes
Chapter 27

2. They’re almost everywhere
Most prokaryotes are microscopic
But what they lack in size they more than make up for in numbers
Biomass is at least 10 times that of all eukaryotes
The number of prokaryotes in a single handful of fertile soil
Is greater than the number of people who have ever lived

3. They’re almost everywhere
Including places too acidic, too salty, too cold, or too hot for most other organisms
2 strains of E. coli are more genetically different than a human and a platypus, lots of adaptations
Figure 27.1

4. Structures Most prokaryotes are unicellular
Although some species form colonies
The three most common of which are spheres (cocci), rods (bacilli), and spirals
1 m
2 m
5 m
(a) Spherical (cocci)
(b) Rod-shaped (bacilli)
(c) Spiral

5. Gram stain Used to identify bacteria and place into 2 groups
Gram positive: have simpler cell walls made of more peptidoglycan
Gram negative: more complex cell walls composed of lipopolysaccharides
Valuable in medicine
gram negative often toxic, with protective outer membrane
more resistant to antibiotics (antibiotics inhibit peptidoglycan cross linking, which prevents cell wall formation)

6. Gram stain (a) Gram-positive. Gram-positive bacteria have
a cell wall with a large amount of peptidoglycan
that traps the violet dye in the cytoplasm. The
alcohol rinse does not remove the violet dye,
which masks the added red dye.
(b)
Gram-negative. Gram-negative bacteria have less
peptidoglycan, and it is located in a layer between the
plasma membrane and an outer membrane. The
violet dye is easily rinsed from the cytoplasm, and the
cell appears pink or red after the red dye is added.
Figure 27.3a, b
Peptidoglycan
layer
Cell wall
Plasma membrane
Protein
Gram-
positive
bacteria
20 m
Outer
membrane
Lipopolysaccharide
negative

7. Cell wall Prevents bursting in hypertonic environment
Covered by a capsule
Sticky layer of polysaccharide and protein, lets them stick to substrate and other cells
Fimbriae and Pili
Short hairlike appendages that help them stick to substrate or each other
Fimbriae are usually more numerous

8. Fimbriae and Pili
200 nm
Fimbriae
Figure 27.5

9. Motility About 50% of prokaryotes are able to move directionally
Some can move up to 50 times their body length per second
Most common structure for movement is flagella
Scattered over cell surface

10. Prokaryote Flagella Different than in eukaryotes
Smaller (1/10th the width)
Not covered by extension of membrane
Motor is the basal apparatus, a system of rings embedded in the cell wall and membrane
Powered by proton pumps
Flagellum
Filament
Hook
Cell wall
Plasma
membrane
Basal apparatus
50 nm
Figure 27.6

11. Taxis Movement toward or away from a stimulus
Chemotaxis is response to chemicals
E. coli demonstrate positive chemotaxis toward other members of their species, causes formation of colonies

12. Internal Organization
Usually lack complex compartmentalization
Do have specialized membranes that perform metabolic functions
Infolding of the plasma membrane similar to the cristae of mitochondria function in cellular respiration
Cyanobacteria have thylakoid membranes
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
0.2 m
1 m
Respiratory
membrane
Thylakoid
membranes
Figure 27.7a, b

13. Prokaryotic genome Only about 1/1000 as much DNA as eukaryotes
Most of the genome consists of a ring of DNA
Chromosome is located in a nucleiod region, part of the cytoplasm
Have DNA called plasmids, consist of only a few genes
Provide antibiotic resistance
Direct metabolism

14. Prokaryotic genome
Figure 27.8
1 m
Chromosome

15. Reproduction Prokaryotes reproduce quickly by binary fission
And can divide every 1–3 hours
In optimal conditions can be as fast as 20 minutes
If continued, a single cell could give rise to a colony that outweighed earth in only 3 days, but thankfully they use up their nutrient supply, poison themselves, or are consumed
Many prokaryotes form endospores
Which can remain viable in harsh conditions for centuries
Cell produces a copy of it’s chromosome and surrounds it by a tough wall
Most can survive in boiling water

16. Endospores
Endospore
0.3 m
Figure 27.9

17. Adaptation Rapid reproduction and horizontal gene transfer
Facilitate the evolution of prokaryotes to changing environments
Studies have found that E. coli today can grow 60 times faster than colonies from 1988