1. Life and Cells What is Life?
Can grow, i.e. increase in size.
Can reproduce.
Responsive to environment.
Metabolism: can acquire and utilize energy.
Schwann and Schleiden: cells basic unit of life
Prokaryotes and eukaryotes from microscopy.
Our focus: prokaryotic cells.
Eubacteria and Archaebacteria

2. The Essential Cell Separates inside from environ. Genetic blueprint
Needed for protein synthesis

3. Bacterial Appearance Size Shape Arrangement 0.2 µm – 0.1 mm
Most 0.5 – 5.0 µm
Shape
Coccus (cocci); rod (bacillus, bacilli); spiral shapes (spirochetes; spirillum, spirilla); filamentous; various odd shapes.
Arrangement
Clusters, tetrads, sarcina, pairs, chains

4. Rods (bacilli) cocci spirochetes
Spirillum
Filamentous
Square

5. Overview of
prokaryotic cell.

6. From Membrane Out: lecture order
Examination of layers of bacterial cell
Starting at cell membrane, working to outside
A look at how cells move
Examination of inside of bacterial cell
A look at how things get into cells
Brief review of eukaryotic cell structure.

7. Structure of phospholipids

8. How phospholipids work
Polar head groups associate with water
but hydrophobic tails associate with
each other to avoid water.
When placed in water, phospholipids
associate spontaneously side by side
and tail to tail to form membranes.

9. Cell Membranes 50/50 lipids and proteins Fluid mosaic model
Effective barrier to large and hydrophilic molecules
O2, CO2, H2O, lipid substances can pass through
Salts, sugars, amino acids, polymers, cannot.
Proteins can be on inner, outer surfaces (peripheral) or transmembrane (integral)
Involved primarily with transport
Degradation and biosynthesis
Site of ATP synthesis

10. Membrane structure

11. Outside the cell membrane: the Cell Wall
Animal cells do not have a cell wall outside the cell membrane.
Plant cells and fungal cells do.
So do most prokaryotic cells, providing structural support and influencing the shape of the cell.

12. Gram stain Gram stain invented by Hans Christian Gram
Divides Eubacteria into two main groups based on stain.
Correlates with two types of cell wall architecture.

13. Division of the Eubacteria: Gram Negative and Gram Positive
Stain is valuable in identification.
Gram positives stain purple; Gram negatives stain pink.
Architecture:
Gram positives have a thick peptidoglycan layer in the cell wall;
Gram negatives have a thin peptidoglycan layer and an outer membrane.
BUT When we say Gram positive…
Cells stain purple? Or have a particular structure?

14. Gram Negative Gram Positive

15. Function and Structure of peptidoglycan
Provides shape and structural support to cell
Resists damage due to osmotic pressure
Provides some degree of resistance to diffusion of molecules
Single bag-like, seamless molecule
Composed of polysaccharide chains cross linked with short chains of amino acids: “peptido” and “glycan”.

16. Monomers of peptidoglycan
Units added to PG as a pair.
NAG: N-acetyl glucosamine
NAM: N-acetyl muramic acid
(NAG + lactic acid)

17. Glycan chains cross-linked with amino acids
G- and G+ vary w/ DAP vs. lysine and at the interbridge.
Note the presence of unusual “D” amino acids.
Peptides attached to NAM.

18. Peptidoglycan is a 3D molecule
Cross links are both horizontal and vertical between glycan chains stacked atop one another.

19. Teichoic acid and lipoteichoic acid
Found in G+ cell wall

20. Teichoic acid and lipoteichoic acid Structure and Function
Polymer of phosphate and ribitol or glycerol R: sugar or amino acid
Lipoteichoic acid covalently attached to membrane lipids.
Major contributor to negative charge of cell exterior.
Appears to function in Ca++ binding

21. Effect of osmotic pressure on cells
Hypotonic: water rushes in; PG prevents cell rupture.
Hypertonic:
water leaves cell, membrane pulls away from cell wall.
plasmolysis

22. Bacteria and Osmotic pressure
Bacteria typically face hypotonic environments
Insides of bacteria filled with proteins, salts, etc.
Water wants to rush in, explode cell.
Protection from hypertonic environments is different, discussed later.
Peptidoglycan provides support
Limits expansion of cell membrane
Lysozyme found in secretions cuts peptidoglycan
Antibiotic penicillin prevents cross linking
Cells in isotonic medium are not harmed

23. Mycobacterium and relatives
Cell Wall Exceptions
Mycobacterium and relatives
Wall contains lots of waxy mycolic acids
Attached covalently to PG
Mycoplasma: no cell wall
Parasites of animals, little osmotic stress
Archaea, the 3rd domain
Pseudomurein and other chemically different wall materials (murein another name for PG)