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.

2 Bacterial Appearance Size –0.2 µm – 0.1 mm –Most 0.5 – 2.0 µm Shape Coccus (cocci); rod (bacillus, bacilli); spiral shapes (spirochetes; spirillum, spirilla); filamentous; various odd shapes. Arrangement Clusters, tetrads, sarcina, pairs, chains

3 Overview of prokaryotic cell.

4 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 Review eukaryotic cell structure on your own.

5 Structure of phospholipids

6 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. et/BiologyPages/L/LipidBilayer.gif

7 Membrane structure

8 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 or transmembrane –Involved primarily with transport –Degradation and biosynthesis –Site of ATP synthesis

9 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, provided structural support and determining the shape of the cell.

10 Division of the Eubacteria: Gram Negative and Gram Positive Gram stain invented by Hans Christian Gram –Gram positive cells stain purple; Gram negatives, pink. 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.

11 ampletour/medical/GramNegat iveEnvelope.gif ampletour/medical/GramPositi veEnvelope.gif Gram Negative Gram Positive

12 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”.

13 Monomers of Peptidoglycan: NAG and NAM

14 Peptidoglycan structure

15 2 nd 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.

16 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.

17 Osmosis-2 Osmosis: special case of the diffusion of water. 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 flows from where it is in high concentration to where it is in low concentration.)

18 Bacteria and Osmotic pressure Bacteria typically face hypotonic environments –Insides of bacteria filled with proteins, salts, etc. –Water wants to rush in, explode cell. Peptidoglycan provides support –Limits expansion of cell membrane –Growth of bacteria and mechanism of penicillin Bacteria need different protection from hypertonic situations –Water leaves the cell; cell membrane shrinks –Lack of water causes precipitation of molecules, death

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

20 PG synthesis Penicillin interferes w/ enzymes attaching new pieces, but old PG is cut anyway… Kablam.

21 Teichoic Acids Polymers found in Gram + cell walls –Either ribitol or glycerol phosphate –Associated with PG Lipoteichoic acid attached to membrane Bind to cations? Help regulate autolysins? –No one knows!

22 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 3 rd domain –Pseudomurein and other chemically different wall materials (murein another name for PG)