1. Chapter 3 Lecture Outline
Cell Structure and Function

2. Basic Structure of a Prokarytic Cell
Ribosomes (+)
Fimbria (+/-)
Additional layer (+/-)
Pili (+/-)
Nucleoid (+)
Inclusion body (+/-)
Plasmid (+/-)
Cell membrane (+)
Flagella (+/-)
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Cell wall (mostly +)

3. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
The Bacterial Cell
Cytoplasm surrounded by envelope
Cytoplasm contains DNA in form of nucleoid
Envelope has lipid membrane boundary
Plus structural cell wall
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

4. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

5. Cross Section through a Gram-Negative Bacterium
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

6. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Cell Membranes
Made of lipid bilayer
Double layer of phospholipids
Separate cytoplasm from outside world
Proteins embedded in membrane
Anchor membranes to envelope
Sense the outside world
Transport materials into cell
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

7. Functions of the Cell Membrane
Permeability barrier
Prevents leakage of cytoplasmic metabolites into the environment
Selective permeability also prevents diffusion of most solutes
Active transport
Structural support
Anchor for membrane proteins
Anchor for cell appendages
Pili
Filaments
Flagella
Detection of environmental signals
Secretion of virulence factors and communication signals
Site of energy conversion (ATP generation)
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

9. Differences between Prokaryotic and Eukaryotic Membranes
Phospholipid composition
Absence of sterols in prokaryotic membranes
In many bacteria hopanoids instead
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

10. Differences between Bacteria and Archaea
Unlike Bacteria (and Eukarya), in which ester linkages bond fatty acids to glycerol, Archaea contain ether-linked lipids
No fatty acids but isoprene (5 carbon hydrocarbon) in Archaea
Some Archaea have lipid monolayers
Ester
H2C-O-C-R O
Ether
H2C-O-C-R
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

11. Bacterial Cell Envelope
Bacterial cell wall
Peptidoglycan
Two major classes
Originally differentiated based on staining characteristic
Gram positive
Thick peptidoglycanl ayer, retains the dye crystal violet
Gram negative
Thin peptidoglycan layer, does not retain the dye crystal violet
Additional layers
S-layer in gram positive bacteria only
Outer membrane in gram negative bacteria only
Slime layers or capsule

12. Peptidoglycan
Strands of alternating repeats of N-acetylglucosamine and N-acetylmuramic acid cross-linked between strands by short peptides
Via N-acetylmuramic acid
4 amino acids
L-alanine, D-alanine, D-glutamic acid, and either L-lysine or meso-diaminopimelic acid

14. Periplasm (some species) Lipoteichoic acids
(embedded in cytoplasmic membrane)
Periplasm

15. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
S-Layer
Composed of symmetrical hexagonal protein subunits
Protection
Molecular sieve
First described in archaea
Recently discovered in gram-positive bacteria
Why only recently?
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

16. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
The Gram-Negative Envelope
Capsule (not all species)
Polysaccharide mainly
Outer Membrane
Lipopolysaccharide (LPS)
In outer leaflet only
Outer membrane proteins
Lipoprotein
Connects peptidoglycan with outer membrane
Thin cell wall
4-amino acid crosslinks in peptidoglycan
Thick periplasm
Plasma membrane OM
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

17. Gram-Negative Envelope
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

18. Lipopolysaccharide (LPS)
Highly variable O-polysaccharide side chains
Core sugars
Conserved lipid A (toxic)
Endotoxin
Fever inducing
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

19. Capsule Optional Most exterior layer
Predominantly made from organized carbohydrate
Sometimes made from protein (e.g. Bacillus anthracis)
Protective
Antiphagocytic
Related structures which serve more for attachment
Slime (loose net work)
Glycocalix (very fine network)

20. Mycobacterial Envelope Structure
Galactan
Arabinan
Outer bilayer with phenolic glycolipids
Capsule with loosely associated phospholipids and phenolic lipids
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

21. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Cytoplasmic contents
Cytoplasmic skeleton
Nucleoid
Plasmids (in some organisms)
Ribosomes
Specialized structures
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

22. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
The Bacterial Cytoskeleton
Determines cell shape
CreS “Crescentin”
Curves inner side of crescent-shaped bacteria
FtsZ
Forms a “Z ring” essential for cell septation
Analog to tubulin
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

23. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
The Bacterial Nucleoid
Single loop of double-stranded DNA
Single molecule of DNA
~4x106 bp in many bacteria
Compacted via supercoiling
Attached to cell envelope
No membrane separates DNA from cytoplasm
Replicates once for each cell division
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

24. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Gene Expression
RNA Polymerase transcribes DNA to mRNA
Ribosome translates RNA to Protein
Processes occur simultaneously
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

25. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Bacterial Ribosomes
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

26. Intracellular Structures Related to Photosynthesis
Cyanobacteria have thylakoids
Extensively folded inner membrane
Contain chlorophyll
Ancestors of chloroplasts
Carboxysomes fix carbon
Use energy to make sugar
Other bacterial photosynthetic pigments
Purple membranes in some
Phycobilisome proteins collect light energy
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

27. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Storage Granules
Intracellular deposits of material
Glycogen (sugar) for energy
PHB (fatty acid polymer) for energy
Polyphosphate to store material
Sulfur for disposal
Carboxysomes,
lipid energy-storage granules
Iridescent sulfur granules
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

28. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Cell Appendages
Proteins
Composed of identical subunit that differ among species
Pili
pilin
Fimbria
Flagella
flagellin
Attachment, specialized pili for plasmid transfer
Attachment
Motility
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

29. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Cell Attachment
Essential for bacterial pathogenicity
Fimbriae, pili
Stalks attach cells to surfaces
Extension of cell cytoplasm
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

30. Cell Motility Flagella Long, helical protein filaments
Attached at ends, or over whole cell
Rotate to propel cell
Proton passage drives rotation
Clockwise or counterclockwise

31. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
Which one of these membranes is NOT found in gram-negative bacteria?
plasma membrane
thylakoid membrane
nuclear membrane
outer membrane
Answer: C
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

32. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
Peptidoglycan is composed primarily of
sugars and amino acids
sugars and nucleic acids
nucleic acids and lipids
Answer: A
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

33. Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz
An extension of the cytoplasm that attaches bacteria to a surface is called a
pilus
flagellum
fimbrium
stalk
Answer: D
Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.