1. Cell structure and function for microbiologists
Prokaryotes
Eukaryotes
Both have the same types of biological
molecules
metabolism, protein synthesis, ATP

2. Eukaryotes have organelles
 Much larger; more complex than
prokaryotes
 Processes compartmentalized into
organelles
 Nucleus
 Protein synthesis (ribosomes, RER, Golgi)
 Mitochondria; chloroplasts
 Lysosomes
 Plasma membranes have different modifications
 Cytoskeleton

3. Eukaryotes may be multicellular
 Cells may be variable within the
organism
 Tissues
 Organs

4. Prokaryotes:
Have no nucleus; genome is circular
No histones
No membrane-bound organelles
Cell wall usually contains peptidoglycan (cell
walls are more complex)
Divide by binary fission

5. Prokaryotes include eubacteria and archae
How do you tell them apart? They’re all small!
morphology
chemical composition
nutritional and energy requirements

6. Typical shapes of bacteria
Most bacteria retain a particular shape; a few
are pleiomorphic

7. Characteristic grouping (or not grouping)

8. Even in groups, bacteria tend to be single-
celled in structure and behavior
Some have “colonial” traits
Well-studied example: myxobacteria
“hunting” colonies
fruiting bodies
Etc.

9. Typical prokaryotic structures
Working from the outside in…

10. Extracellular components
Protection
dehydration
immune mechanisms
Attachment
Glycocalyx- polysaccharide, protein
capsule if organized
slime layer if not
May contribute to virulence

12. Some bacteria are motile (due to flagella)
Bacteria vary in the way flagella are attached
How they move: running, tumbling, swarming
Can move toward or away from light or
chemical stimuli
Flagellin protein is unique to prokaryotes

13. Cocci do not have flagella
Peritrichous monotrichous
(or amphi, or lophotrichous

14. Pili- attachment; motility; conjugation

15. Cell membrane structure is similar in structure
and function to that of eukaryotes
Phospholipid bilayer
(everything moves through it, since there
are no organelles)
carrier proteins
generally involve proton motive force (i.e,
require energy and moving against the
concentration gradient)

17. Cell wall- hallmark of prokaryotes
Their reaction with Gram stain allows bacteria
to be divided into two groups
Positive-lots of peptidoglycan
Negative- thin layer, with an outer membrane
and “periplasmic space” in between
Many secreted proteins are found here

18. Structure of peptidoglycan

19. Gram-positive cell wall

21. Outer membrane is made of lipopolysaccharide
(LPS)
Porins allow molecules to pass through outer
membrane
LPS is protective
lipid A- strong inflammatory response
(endotoxin)
O-linked polysaccharide- antigenic

22. Significance of Gram-positive vs Gram-negative
antibiotic sensitivity
sensitivity to lysozyme
reaction with Gram reagents
crystal violet
iodine
alcohol
safranin

24. Mycoplasma do not have a cell wall
Lots of variety in Achaea- but none have
peptidoglycan

25. Internal components
Nucleoid- with single, circular, supercoiled
DNA molecule
Many bacteria have plasmids
small, extrachromosomal, circular
piece of DNA
genes present are usually not required
but may be advantageous
(antibiotic resistance, resistance to metals)
Now used for genetic engineering

26. Ribosomes
Involved in protein synthesis
Prokaryotic ribosomes are smaller than
eukaryotic (70S vs 80S)
Some antibiotics bind to the 70S ribosome
How does that affect bacteria?

27. No membrane-bound organelles
Some have storage granules
Some aquatic bacteria have gas vesicles
Some have endospores (soil bacteria) that
enable them to lie dormant under
“unfavorable” conditions
NOT a reproductive structure

28. Summary
 Eukaryotes have membrane-bound
organelles
 Eukaryotes may be multicellular with highly
specialized cells
 Prokaryotes have simple shapes and are
classified according to their morphology
 Certain structures are unique to prokaryotes