1. Ch 4 Functional Anatomy of Prokaryotic and Eukaryotic Cells

2. Objectives
Compare and contrast the overall cell structure of prokaryotes and eukaryotes.
Identify the three basic shapes of bacteria.
Describe structure and function of the glycocalyx, flagella, axial filaments, fimbriae, and pili.
Compare and contrast the cell walls of gram-positive bacteria, gram-negative bacteria, acid-fast bacteria, and mycoplasmas.
Differentiate between protoplast, spheroplast, and L form.
Describe the structure, chemistry, and functions of the prokaryotic plasma membrane.
Identify the functions of the nuclear area, ribosomes, and inclusions.
Describe the functions of endospores, sporulation, and endospore germination.
What you should remember from Bio 31:
Define organelle. Describe the functions of the nucleus, endoplasmic reticulum, ribosomes, Golgi complex, lysosomes, vacuoles, mitochondria, chloroplasts, peroxisomes. Explain endosymbiotic theory of eukaryotic evolution.

3. Comparing Prokaryotic and Eukaryotic Cells
Common features:
DNA and chromosomes
Cell membrane
Cytosol and Ribosomes
Distinctive features: ?

4. Prokaryotes One circular chromosome, not membrane bound No histones
No organelles
Peptidoglycan cell walls
Binary fission

5. Size, Shape, and Arrangement
Average size: µm  µm
Three basic shapes
Bacillus, -i
Coccus, -i
Spirals (Vibrio, Spirillum, Spirochete)
Most monomorphic, some pleomorphic
Variations in cell arrangements (esp. for cocci)
Review Figs. 4.1, 4.2, and 4.4

6. Spiral Bacteria
Figure 4.4

7. Pleomorphic Corynebacteria
Monomorphic E. coli

8. Cell Arrangement

9. External Structures located outside of cell wall Glycocalyx
Flagellum /-a
Axial filaments
Fimbria /-ae
Pilus /-i

10. Glycocalyx
Many bacteria secrete external surface layer composed of sticky polysaccharides, polypeptide, or both
Capsule: organized and firmly attached to cell wall
Slime layer: unorganized and loosely attached
Allows cells to attach  key to biofilms
Prevents phagocytosis  virulence factor
E.g.: B. anthracis, S. pneumoniae, S. mutans

11. Flagellum – Flagella Anchored to wall and membrane
Number and placement determines if atrichous, monotrichous, lophotrichous, amphitrichous, or peritrichous
Fig 4.7

12. Flagellar Arrangement
_______
___________

13. Motility Due to rotation of flagella
Mechanism of rotation: “Run and tumble”
Move toward or away from stimuli (taxis)
Chemotaxis (phototaxis and magnetotaxis)
Flagella proteins are H antigens (e.g., E. coli O157:H7)

14. “Run and Tumble”
Fig 4.9

15. Axial Filaments Fimbriae and Pili Fimbriae allow attachment
Pili are used to transfer DNA from one cell to another
Endoflagella
In spirochetes
Anchored at one end of a cell
Rotation causes cell to move
Fig 4.10

16. Cell Wall Rigid for shape & protection  prevents osmotic lysis
Consists of Peptidoglycan (murein)  polymer of 2 monosaccharide subunits
N-acetylglucosamine (NAG) and
N-acetylmuramic acid (NAM)
Linked by polypeptides (forming peptide cross bridges) with tetrapeptide side chain attached to NAM
Fully permeable to ions, aa, and sugars (Gram positive cell wall may regulate movement of cations)

17. Fig 4.13

18. Gram + Cell Wall Gram – Cell Wall
Thick layer of peptidoglycan
Negatively charged teichoic acid on surface
Thin peptidoglycan
Outer membrane
Periplasmic space

19. Gram-Positive Cell Walls
Teichoic acids
Lipoteichoic acid links to plasma membrane
Wall teichoic acid links to peptidoglycan
May regulate movement of cations
Polysaccharides provide antigenic variation
Fig.4.13b

20. Gram-negative Cell Wall
Lipid A of LPS acts as endotoxin; O polysaccharides are antigens for typing, e.g., E. coli O157:H7
Gram neg. bacteria are less sensitive to medications because outer membrane acts as additional barrier.
LPS layer = outer layer of outer membrane
(protein rich gel-like fluid)
Fig 4.13

21. Gram Stain Mechanism Crystal violet-iodine crystals form in cell.
Gram-positive
Alcohol dehydrates peptidoglycan
CV-I crystals do not leave
Gram-negative
Alcohol dissolves outer membrane and leaves holes in peptidoglycan.
CV-I washes out
For further details and practical application see lab

22. Bacteria with No Cell Wall: Mycoplasmas
Instead, have cell membrane which incorporates cholesterol compounds (sterols), similar to eukaryotic cells
Cannot be detected by typical light microscopy
Mycoplasmas cannot be detected by the naked eye or even by typical light microscopy. The morphology of mycoplasma colonies is often likened to a "fried-egg" because they form a dense central core, which penetrates downward into the agar, surrounded by a circular spreading area that is lighter in color.
When Mycoplasma species were first cultured, they were thought to have been viruses because of their size. Mycoplasma pneumoniae is a very small bacterium, in the class Mollicutes. This class of organisms lack a peptidoglycan cell wall present on all other firmicute bacteria. Instead, it has a cell membrane which incorporates cholesterol compounds, similar to eukaryotic cells. Lacking a cell wall, these organisms are resistant to the effects of penicillins and other beta-lactam antibiotics, which act by disrupting the bacterial cell wall.
M. pneumoniae has one of the smallest genomes known, with 816 kilobase pairs (kbs). Its genome and proteome has been fully characterized. It uses some unique genetic code, making its code more similar to mitochondria than to other bacteria. It lacks the cellular machinery for making many essential compounds. Because of this, it is an obligate parasite. No mycoplasma is found free-living. In this respect, mycoplasma is more similar to viruses than to bacteria.
M. pneumoniae is spread through respiratory droplet transmission. Once attached to the mucosa of a host organism, M. pneumonia extracts nutrients, grows and reproduces by binary fission. Attachment sites include the upper and lower respiratory tract, causing pharyngitis, bronchitis and pneumonia. The infection caused by this bacterium is called atypical pneumonia because of its protracted course and lack of sputum production and wealth of extra-pulmonary symptoms. Chronic mycoplasma infections have been implicated in the pathogenesis of rheumatoid arthritis and other rheumatological diseases.
Second generation macrolide antibiotics and second generation quinolones are effective treatments. Disease from mycoplasma is usually mild to moderate in severity.
Mycoplasma pneumoniae lacks a cell wall which leads to osmotic instability. The combination of these unique characteristics creates a different scenario for treatment of a mycoplasmal infection than other bacteria. The lack of a cell wall prevents the utilization of a B-lactam antibiotic, such as penicillin and cycloserine, because they act specifically to disrupt the cell wall. The use of cholesterol in M. pneumoniae, however, allows for a different avenue for antibiotic therapies usually ineffective on bacteria, such as the use of polyenes.
The absence of a cell wall is likely to facilitate a bacterium to host interaction through which compounds can be exchanged. This transfer can include not only the nutrients and supplementary amino acids, etc. that is necessary for the support of bacterial growth, but also toxic metabolic compounds. It is thought that this bacterial surface parasitism causes severe damage to the host cell, however, not one toxin has been identified as the culprit.
This EM shows some typically pleomorphic mycoplasmas, in this case M. hyorhinis

23. Acid-fast Cell Walls Genus Mycobacterium and Nocardia
mycolic acid (waxy lipid) covers thin peptidoglycan layer
Do not stain well with Gram stain  use acid-fast stain

24. Damage to Cell Wall Lysozyme digests disaccharide in peptidoglycan.
Penicillin inhibits peptide bridges in peptidoglycan.

25. Internal Structures: Cell Membrane
Analogous to eukaryotic cell membrane:
Phospholipid bilayer with proteins (Fluid mosaic model)
Permeability barrier (selectively permeable)
Diffusion, osmosis and transport systems
Different from eukaryotic cell membrane:
Role in Energy transformation (electron transport chain for ATP production)
Damage to the membrane by alcohols, quaternary ammonium (detergents), and polymyxin antibiotics causes leakage of cell contents.

26. Fig 4.14

27. Movement of Materials across Membranes
See Bio 31!
Diffusion (simple and facilitated), osmosis, active transport , isotonic, hypotonic etc.
Review on your own if necessary (pages 92 – 94)

28. Cytoplasm and Internal Structures
Location of most biochemical activities
Nucleoid: nuclear region containing DNA (up to 3500 genes). Difference between human and bacterial chromosome?
Plasmids: small, nonessential, circular DNA (5-100 genes); replicate independently
Ribosomes (70S vs. 80S)
Inclusion bodies: granules containing nutrients, monomers, Fe compounds (magnetosomes)

29. Compare to Fig. 4.6

30. Endospores
Dormant, tough, non-reproductive structure;  germination  vegetative cells
Spore forming genera: __________
Resistance to UV and  radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants
Relationship to disease
Sporulation: Endospore formation
Germination: Return to vegetative state

31. Sporulation
In response to starvation, B. subtilis differentiates into a dormant stress-resistant cell-type known as a spore. Cells initiate spore formation with an asymmetric cell division that generates a large cell (the mother cell) and a small cell (the prospective spore or forespore). Initially these two cells lie side-by-side but later in development the mother cell engulfs the forespore in a phagocytic-like process to produce a cell-within-a-cell. The mother then nurtures the forespore as it prepares for dormancy. Once the spore is fully mature, the mother cell lyses. We use this elegant morphological process to address basic questions in bacterial differentiation.
Fig. 4.21

32. Green endospores within pink bacilli
Green endospores within pink bacilli. Many spores have already been released from the vegetative cells

33. The Eukaryotic Cell the end See Bio 31!
Review on your own if necessary (pages 98 – 106)
the end