I. Cell Shape and Size

1. © 2012 Pearson Education, Inc. I. Cell Shape and Size • 3.1 Cell Morphology • 3.2 Cell Size and the Significance of Smallness

2. Figure 3.1 Spirochete Coccus Hypha Stalk Rod Budding and appendaged bacteria Spirillum Filamentous bacteria © 2012 Pearson Education, Inc.

3. © 2012 Pearson Education, Inc. 3.1 Cell Morphology • Morphology typically does not predict physiology, ecology, phylogeny, etc. of a prokaryotic cell • Selective forces may be involved in setting the morphology • Optimization for nutrient uptake (small cells and those with high surface-to-volume ratio) • Swimming motility in viscous environments or near surfaces (helical or spiral-shaped cells) • Gliding motility (filamentous bacteria)

4. © 2012 Pearson Education, Inc. 3.2 Cell Size and the Significance of Smallness • Size range for prokaryotes: 0.2 µm to >700 µm in diameter • Most cultured rod-shaped bacteria are between 0.5 and 4.0 µm wide and <15 µm long • Examples of very large prokaryotes • Epulopiscium fishelsoni (Figure 3.2a) • Thiomargarita namibiensis (Figure 3.2b) • Size range for eukaryotic cells: 10 to >200 µm in diameter

5. © 2012 Pearson Education, Inc. 3.2 Cell Size and the Significance of Smallness • Surface-to-Volume Ratios, Growth Rates, and Evolution • Advantages to being small (Figure 3.3) • Small cells have more surface area relative to cell volume than large cells (i.e., higher S/V) • support greater nutrient exchange per unit cell volume • tend to grow faster than larger cells

6. © 2012 Pearson Education, Inc. 3.3 The Cytoplasmic Membrane in Bacteria and Archaea • Cytoplasmic membrane: • Thin structure that surrounds the cell • 6–8 nm thick • Vital barrier that separates cytoplasm from environment • Highly selective permeable barrier; enables concentration of specific metabolites and excretion of waste products

7. © 2012 Pearson Education, Inc. 3.3 The Cytoplasmic Membrane • Composition of Membranes • General structure is phospholipid bilayer (Figure 3.4) • Contain both hydrophobic and hydrophilic components • Can exist in many different chemical forms as a result of variation in the groups attached to the glycerol backbone • Fatty acids point inward to form hydrophobic environment; hydrophilic portions remain exposed to external environment or the cytoplasm Animation: Membrane Structure

8. Figure 3.4 Glycerol Fatty acids Phosphate Ethanolamine Hydrophilic region Hydrophobic Fatty acids region Hydrophilic region Glycerophosphates Fatty acids © 2012 Pearson Education, Inc.

9. © 2012 Pearson Education, Inc. 3.3 The Cytoplasmic Membrane • Cytoplasmic Membrane (Figure 3.5) • 6–8 nm wide • Embedded proteins • Stabilized by hydrogen bonds and hydrophobic interactions • Mg2+ and Ca2+ help stabilize membrane by forming ionic bonds with negative charges on the phospholipids • Somewhat fluid

10. Figure 3.5 Out Phospholipids Hydrophilic groups 6–8 nm Hydrophobic groups In Integral Phospholipid membrane proteins molecule © 2012 Pearson Education, Inc.

11. Figure 3.6 Ester Ether Bacteria Archaea Eukarya © 2012 Pearson Education, Inc.

12. Figure 3.7d Out Glycerophosphates Phytanyl Membrane protein In Lipid bilayer © 2012 Pearson Education, Inc.

13. Figure 3.7e Out Biphytanyl In Lipid monolayer © 2012 Pearson Education, Inc.

14. © 2012 Pearson Education, Inc. 3.4 Functions of the Cytoplasmic Membrane • Permeability Barrier (Figure 3.8) • Polar and charged molecules must be transported • Transport proteins accumulate solutes against the concentration gradient • Protein Anchor • Holds transport proteins in place • Energy Conservation

15. © 2012 Pearson Education, Inc. III. Cell Walls of Prokaryotes • 3.6 The Cell Wall of Bacteria: Peptidoglycan • 3.7 The Outer Membrane • 3.8 Cell Walls of Archaea

16. © 2012 Pearson Education, Inc. 3.6 The Cell Wall of Bacteria: Peptidoglycan Peptidoglycan (Figure 3.16) • Rigid layer that provides strength to cell wall • Polysaccharide composed of • N-acetylglucosamine and N-acetylmuramic acid • Amino acids • Lysine or diaminopimelic acid (DAP) • Cross-linked differently in gram-negative bacteria and gram-positive bacteria (Figure 3.17)

17. Figure 3.17 Polysaccharide backbone Interbridge Peptides Escherichia coli (gram-negative) Staphylococcus aureus (gram-positive) Y Peptide bonds X Glycosidic bonds © 2012 Pearson Education, Inc.

18. © 2012 Pearson Education, Inc. 3.6 The Cell Wall of Bacteria: Peptidoglycan • Gram-Positive Cell Walls (Figure 3.18) • Can contain up to 90% peptidoglycan • Common to have teichoic acids (acidic substances) embedded in the cell wall • Lipoteichoic acids: teichoic acids covalently bound to membrane lipids

19. Figure 3.18 Peptidoglycan cable Ribitol Teichoic acid Peptidoglycan Wall-associated protein Lipoteichoic acid Cytoplasmic membrane © 2012 Pearson Education, Inc.

20. © 2012 Pearson Education, Inc. 3.6 The Cell Wall of Bacteria: Peptidoglycan • Prokaryotes That Lack Cell Walls • Mycoplasmas • Group of pathogenic bacteria • Thermoplasma • Species of Archaea

21. © 2012 Pearson Education, Inc. 3.7 The Outer Membrane • Total cell wall contains ~10% peptidoglycan (Figure 3.20a) • Most of cell wall composed of outer membrane (aka lipopolysaccharide [LPS] layer) • LPS consists of core polysaccharide and O-polysaccharide • LPS replaces most of phospholipids in outer half of outer membrane • Endotoxin: the toxic component of LPS

22. Figure 3.20a O-polysaccharide Core polysaccharide Out Lipid A Protein Lipopolysaccharide (LPS) Porin 8 nm Outer membrane Cell wall Phospholipid Peptidoglycan Periplasm Lipoprotein Cytoplasmic membrane In © 2012 Pearson Education, Inc.

23. © 2012 Pearson Education, Inc. 3.7 The Outer Membrane • Structural differences between cell walls of gram-positive and gram-negative Bacteria are responsible for differences in the Gram stain reaction

24. © 2012 Pearson Education, Inc. 3.8 Cell Walls of Archaea • No peptidoglycan • Typically no outer membrane • Pseudomurein • Polysaccharide similar to peptidoglycan (Figure 3.21) • Composed of N-acetylglucosamine and N-acetyltalosaminuronic acid • Found in cell walls of certain methanogenic Archaea • Cell walls of some Archaea lack pseudomurein

25. © 2012 Pearson Education, Inc. 3.8 Cell Walls of Archaea • S-Layers • Most common cell wall type among Archaea • Consist of protein or glycoprotein • Paracrystalline structure (Figure 3.22)

26. Figure 3.22 © 2012 Pearson Education, Inc.

27. © 2012 Pearson Education, Inc. 3.9 Cell Surface Structures • Capsules and Slime Layers • Polysaccharide layers (Figure 3.23) • May be thick or thin, rigid or flexible • Assist in attachment to surfaces • Protect against phagocytosis • Resist desiccation

28. Figure 3.23 Cell Capsule © 2012 Pearson Education, Inc.

29. © 2012 Pearson Education, Inc. 3.9 Cell Surface Structures • Fimbriae • Filamentous protein structures (Figure 3.24) • Enable organisms to stick to surfaces or form pellicles

30. Figure 3.24 Flagella Fimbriae © 2012 Pearson Education, Inc.

31. © 2012 Pearson Education, Inc. 3.9 Cell Surface Structures • Pili • Filamentous protein structures (Figure 3.25) • Typically longer than fimbriae • Assist in surface attachment • Facilitate genetic exchange between cells (conjugation) • Type IV pili involved in twitching motility

32. Figure 3.25 Virus- covered pilus © 2012 Pearson Education, Inc.