1. Small, smaller, smallest
Science uses the metric system
Each unit differs by 1000x (103)
Length: meter, millimeter, micrometer, nanometer
Molecules are too small to talk about length
Units are molecular weight: grams/mol
i.e. how much do x 1023 molecules weigh?
What sizes are we talking about?
We can see things about 0.1 mm (100 µm)
Bacteria are generally 1 – 5 µm ( mm)
We need special microscopes to see smaller than that.

2. Something can’t be smaller than the parts it is made of!
Sand is used to make bricks, and bricks are assembled to make a house. A house can’t be smaller than a brick; a brick can’t be smaller than grains of sand.
Likewise, small molecules are combined to make polymers and polymers are used to make cells.
cic.nist.gov/lipman/sciviz/scan/jun24_ptC1a.jpg

3. In the world of small, what’s big?
Cells of eukaryotic organisms are big
Nerve cells can be quite long
White blood cells are about 10 µm in diameter
An amoeba may be around 20 µm
Prokaryotes and cell organelles are smaller
E. coli is about 1 µm long
A mitochondrion is about the same size
Particles are smaller
Viruses range from 20 to 200 nm (0.02 – 0.2 µm)
Ribosomes, found inside cells, are about 20 nm

4. In the world of small, what’s smaller?
Ribosomes, viruses, cell walls are made of polymers
Ribosomes and viruses are combinations of proteins and nucleic acids
Cell walls are made of large molecules like peptidoglycan and lipopolysaccharide
Polymers are larger than the monomers they are made of
Proteins range from 10,000 to 500,000 MW
Bacterial DNA is over 1 mm long! (but very skinny)
Polysaccharides can be > 100,000 MW (grams/mol)

5. In the world of small, what’s smallest?
These are all small molecules ranging from 18 g/mol to 1,000 g/mol
Water, oxygen gas, nitrogen gas
Sugars (glucose, sucrose, etc.)
Amino acids
Nucleotides
Fatty acids, cholesterol, (even phospholipids aren’t big)
Organic acids found in metabolism
Vitamins
Antibiotics and most other drugs

6. 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

7. 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

8. Overview of
prokaryotic cell.

9. 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.

10. Structure of phospholipids

11. 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.

12. 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

13. Membrane structure

14. 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.

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

16. Gram Negative Gram Positive

17. 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”.

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

19. 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.

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

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

22. 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

23. 2nd Law of Thermodynamics
All things tend toward entropy (randomness).
Molecules move (diffuse) from an area of high concentration to areas of low concentration.
Eventually, molecules become randomly distributed unless acted on by something else.

24. Osmosis Osmosis: a special case of diffusion
Water flows from where it is more concentrated (a dilute solution) to where it is less concentrated (a solution with many solute molecules)
Osmosis requires a “semi-permeable” membrane
One which water, but not dissolved substances, can pass through.
Cells typically have lots of dissolved substances; the net flow of water is into the cell (unless resisted).

25. Osmosis
Yellow spots cannot move through membrane in middle. Water moves into compartment where spots are most concentrated, trying to dilute them, make concentration on both sides of the membrane the same.
In this example, gravity limits how much water can flow. In a bacterium, the peptidoglycan provides the limit.

26. Osmosis definitions
Movement of water across a semi permeable membrane.
If the environment is:
Isotonic: No NET flow.
Hypertonic: Water flows OUT of cell.
Hypotonic: Water flows IN.
Water can flow both ways; we are considering NET flow.
Terms are comparative terms, like the word “more”.

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

28. 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
Growth of bacteria and mechanism of penicillin
Penicillin inhibits crosslinking, weakens wall
Resting bacteria aren’t making new wall, aren’t vulnerable

29. 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)