1. Procaryotic Cell Structure and Function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 3
Procaryotic Cell Structure and Function

2. A Preview of Procaryotic Cell Structure and Function
Procaryotes differ from eucaryotes in many traits including size and lack of internal membrane systems
Procaryotes are divided into Bacteria and Archaea
Bacteria are divided into 2 groups based on their Gram stain reaction

4. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.2

5. Size, Shape, and Arrangement
Cocci (coccus) – spheres
Diplococci (diplococcus) – pairs
Streptococci – chains
Staphylococci – grape-like clusters
Tetrads – 4 cocci in a square
Sarcinae – cubic configuration of 8 cocci

6. Size, Shape, and Arrangement
Bacilli (bacillus) – rods
-coccobacilli – very short rods
-vibrios – resemble rods, comma shaped
Spirilla (spirillum) – rigid helices
Spirochetes – flexible helices
Mycelium – network of long, multinucleate filaments

7. Size, Shape, and Arrangement
Pleomorphic – organisms that are variable in shape

8. Size 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
Few very large prokaryotes; examples include
Epulopiscium fishelsoni
Thiomargarita namibiensis
Size range for eukaryotic cells: 10 to > 200 µm in diameter

10. largest –
50 μm in
diameter
smallest –
0.3 μm in

11. Figure 3.4

12. Procaryotic Cell Membranes
Membranes are an absolute requirement for all living organisms
Plasma membrane encompasses the cytoplasm
Some procaryotes also have internal membrane systems

13. Composition Phospholipids
Contain both hydrophobic and hydrophilic components
Can exist in many different chemical forms due to variation in the groups attached to the glycerol backbone
Fatty acids point inward to form hydrophobic environment

14. Bacterial Phopholipids
polar ends
interact with water
hydrophilic
nonpolar ends
insoluble in water
hydrophobic
Figure 3.6

15. General Structure of Phospholipids

16. Functions of the plasma membrane
Separation of cell from its environment
Selectively permeable barrier
some molecules are allowed to pass into or out of the cell
transport systems aid in movement of molecules

17. More functions…
Location of crucial metabolic processes
Special receptor molecules in the membrane

18. Fluid Mosaic Model of Membrane Structure
Lipid bilayer in which proteins float
Figure 3.5

19. Membrane proteins Peripheral proteins Integral proteins
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Membrane proteins
Peripheral proteins
loosely associated with the membrane and easily removed
Integral proteins
embedded within the membrane and not easily removed

20. Bacterial Membranes differ from eucaryotes in lacking sterols
do contain hopanoids, sterol-like molecules
a highly organized, asymmetric system which is also flexible and dynamic

21. Other membrane lipids
Figure 3.7

22. Internal Membranous Structures
Plasma membrane infoldings
Observed in many photosynthetic bacteria
Nitrifying bacteria
Methanotrophic bacteria

23. Plasma membrane infoldings: observed in many photosynthetic bacteria
Figure 3.8

24. Archaeal membranes Composed of unique lipids
Some have a monolayer structure instead of a bilayer structure

25. Figure 3.9

26. Figure 3.10

27. Figure 3.11

28. Cytoplasmic Matrix
Substance in which nucleoid, ribosomes and inclusion bodies are suspended
Lacks organelles bound by unit membranes
Composed largely of water

29. Inclusion bodies
Granules of organic or inorganic material that are stockpiled by the cell for future use
Some are enclosed by a single-layered membrane

30. Organic inclusion bodies
Glycogen
polymer of glucose units
Poly-β-hydroxybutyrate (PHB)
polymers of β-hydroxybutyrate

31. Organic inclusion bodies
cyanophycin granules
large polypeptides containing about equal quantities of arginine and aspartic acid
carboxysomes
contain the enzyme ribulose-1,5,-bisphosphate carboxylase (Rubisco), enzyme used for CO2 fixation

32. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.13

33. Organic inclusion bodies
gas vacuoles
found in cyanobacteria and some other aquatic procaryotes
provide buoyancy
aggregates of hollow cylindrical structures called gas vesicles

34. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Freeze-fracture preparation of Anabaena flos-aquae; clusters of cigar-shaped gas vesicles form gas vacuoles
Figure 3.14

35. Inorganic inclusion bodies
Polyphosphate granules
linear polymers of phosphates
Sulfur granules
- source of energy (purple sulfur bacteria
magnetosomes
contain iron in the form of magnetite
used to orient cells in magnetic fields

36. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Aquaspirillum magnetotacticum; MP=magnetite particles; OM=outer membrane; P=periplasmic space; CM=cytoplasmic membrane
TA 3.2 (a)

37. TA 3.2 (b) Isolated magnetosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Isolated magnetosomes
TA 3.2 (b)

38. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Bacteria migrating in waves when exposed to a magnetic field
TA 3.2 (c)

39. Ribosomes Complex structures consisting of protein and RNA
Sites of protein synthesis
Smaller than eucaryotic ribosomes
procaryotic ribosomes  70S
eucaryotic ribosomes  80S
S = Svedburg unit

40. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.15

41. The Nucleoid Irregularly shaped region Location of chromosome
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Nucleoid
Irregularly shaped region
Location of chromosome
usually 1/cell
Not membrane-bound
Figure 3.4

42. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Procaryotic chromosomes are located in the nucleoid, an area in the cytoplasm
Figure 3.14a: growing Bacillus cells stained with HCl-Giemsa and viewed with light microscope
Figure 3.14b: section of growing E. coli immunostained specifically for DNA; viewed with TEM
Figure 3.15c: model of 2 nucleoids in an actively growing E. coli cell
Figure 3.16

43. The procaryotic chromosome
Closed circular, double-stranded DNA molecule
Looped and coiled extensively
Nucleoid proteins probably aid in folding
nucleoid proteins differ from histones

44. Plasmids Closed circular or linear DNA molecules
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Plasmids
Closed circular or linear DNA molecules
Replicate independently of chromosome
Have relatively few genes present
Genes on plasmids are not essential to host but may confer selective advantage (e.g., drug resistance)

45. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Table 3.3

46. The Bacteria Cell Wall
rigid structure that lies just outside the plasma membrane
Figure 3.4

47. Functions of cell wall Provides characteristic shape to cell
Protects the cell from osmotic lysis
Protects from toxic compounds and pathogens
May also contribute to pathogenicity
A site for antibiotic action
Some organisms lack cell walls

48. Cell walls of Bacteria
Bacteria are divided into two major groups based on the response to gram-stain procedure.
gram-positive bacteria stain purple
gram-negative bacteria stain pink
Staining reaction due to cell wall structure

49. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.17

50. Peptidoglycan
Figure 4.18

51. Peptidoglycan (Murein) Structure
Meshlike polymer composed of identical subunits
Contains N-acetyl glucosamine and N-acetylmuramic acid and several different amino acids
Chains of peptidoglycan subunits are cross linked by peptides

52. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Top: E. coli peptidoglycan; direct cross-linking, typical of many gram-negative bacteria
Bottom: Staphylococcus aureus peptidoglycan
NAM= N-acetylglucosoamine; NAG= N-acetylmuramic acid
Figure 3.20

53. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.21

54. Gram-Positive Cell Walls
composed primarily of peptidoglycan
may also contain large amounts of teichoic acids
some gram-positive bacteria have layer of proteins on surface of peptidoglycan
Isolated cell wall from Bacillus megaterium; latex spheres are 0.25 micrometer in diameter
Figure 3.22

55. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.23

56. teichoic acids polymers of glycerol or ribitol joined by
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
teichoic acids
polymers of glycerol
or ribitol joined by
phosphate groups
Figure 3.24

57. Gram-Negative Cell Walls
Consist of a thin layer of peptidoglycan surrounded by an outer membrane
Outer membrane composed of lipids, lipoproteins, and lipopolysaccharide (LPS)
No teichoic acids

58. Gram-Negative Cell Walls
More complex than Gram + walls
Peptidoglycan is ~2-5% of wall weight
Periplasmic space differs from that in gram + cells
may constitute 20-40% of cell volume
many enzymes present in periplasm

59. Gram-Negative Cell Walls
Outer membrane lies outside the thin peptidoglycan layer
Braun’s lipoproteins connect outer membrane to peptidoglycan

60. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.25

61. Lipopolysaccharides (LPSs)
Consists of three parts
lipid A
core polysaccharide
O side chain (O antigen)

62. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
LPS from Salmonella: Abe=abequose; Gal=galactose; Glc=glucose; GlcN=glucosamine; Hep=heptulose; KDO=2-keto-3-deoxyoctonate; Man=mannose; NAG=N-acetyleglucosamine; P=phosphate; Rha=rhamnose
Figure 3.27

63. Importance of LPS Protection from host defenses (O antigen)
Contributes to negative charge on cell surface (core polysaccharide)
Helps stabilize outer membrane structure (lipid A)
Can act as an exotoxin (lipid A)

64. Other Characteristics of the Outer Membrane
More permeable than plasma membrane due to presence of porin proteins and transporter proteins
porin proteins form channels through which small molecules ( daltons) can pass

65. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.28

66. Molecular Model of Porin Proteins

67. Archaeal cell walls Lack peptidoglycan
Cell wall varies from species to species but usually consists of complex heteropolysaccharides
Methanogens have walls containing pseudomurein

68. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.30

69. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.31

70. Protein Secretion in Procaryotes
Numerous protein secretion pathways have been identified
four major pathways are:
Sec-dependent pathway
type II pathway
type I (ABC) protein secretion pathway
type III protein secretion pathway

71. Overview of Bacterial Protein Secretion
Gram+ and Gram- bacteria have different problems secreting proteins based on the differences between the structure of their walls
Both use Sec-dependent pathway
All protein secretion systems require energy

72. Sec-Dependent Pathway
Also called general secretion pathway
Translocates proteins from cytoplasm across or into plasma membrane
Secreted proteins synthesized as preproteins having amino-terminal signal peptide
signal peptide delays protein folding
chaperone proteins keep preproteins unfolded

73. Sec-Dependent Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sec-Dependent Pathway
secA translocates preprotein through the plasma membane
When preprotein emerges from plasma membrane a signal peptidase removes the signal peptide

74. Sec-Dependent Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sec-Dependent Pathway
Sec-dependent pathway of E. coli
Figure 3.32

75. Protein Secretion in Gram- bacteria
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Protein Secretion in Gram- bacteria
5 secretion pathways have been identified in gram- bacteria
type II and V pathways transport proteins across outer membrane that were translocated across plasma membrane by Sec-dependent pathway
types I and III pathways are Sec-independent
type IV pathway usually functions independently of the Sec pathway

76. Type II Protein Secretion Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Type II Protein Secretion Pathway
Present in a number of plant and animal pathogens
transports proteins from periplasmic across outer membrane
observed in some gram-negative bacteria, including some pathogens
complex systems consisting of up to proteins
most are integral membrane proteins

77. Type V Protein Secretion Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Type V Protein Secretion Pathway
Most recently discovered protein secretion system
Rely on Sec-dependent pathway to move proteins across plasma membrane
When proteins are in periplasmic space many can form a channel in outer membrane through which they transport themselves; hence they are called autotransporters

78. ABC Protein Secretion Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ABC Protein Secretion Pathway
also called Type I Protein Secretion Pathway
ubiquitous in procaryotes
transports proteins from cytoplasm across both plasma membrane and outer membrane
secreted proteins have C-terminal secretion signals
Gram+ bacteria use a modified version of this pathway to translocate proteins across the plasma membrane

79. Type III Protein Secretion Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Type III Protein Secretion Pathway
secretes virulence factors of gram-negative bacteria from cytoplasm, across both plasma membrane and outer membrane, and into host cell
some type III secretion machinery is syringe-shaped
secreted proteins thought to move through a translocation channel

80. Type IV Protein Secretion Pathway
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Type IV Protein Secretion Pathway
Type IV pathways are unique because they secrete proteins and transfer DNA during conjugation
Type IV systems are made of many different proteins, some of which form a syringe-like structure

81. Protein Secretion Systems of Gram-Negative Bacteria
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Protein Secretion Systems of Gram-Negative Bacteria
Figure 3.33

82. Components External to Cell Wall
Figure 3.4

83. Capsules, Slime Layers, and S-Layers
usually composed of polysaccharides
well organized and not easily removed from cell
Slime layers
similar to capsules except diffuse, unorganized and easily removed

84. Bacterial Capsules
Figure 3.34

85. Bacterial capsules

86. Glycocalyx
network of polysaccharides extending from the surface of the cell
a capsule or slime layer composed of polysaccharides can also be referred to as a glycocalyx

87. Bacterial Glycocalyx
Figure 3.35

88. Capsules, Slime Layers, and S-Layers
regularly structured layers of protein or glycoprotein
in bacteria the S layer is external to the cell wall
common among Archaea, where they may be the only structure outside the plasma membrane

89. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
S-layer of Deinococcus radiodurans; electron micrograph after shadowing
Figure 3.36

90. Functions Protection from host defenses (e.g., phagocytosis)
Protection from harsh environmental conditions (e.g., desiccation)
Attachment to surfaces

91. More functions…
Protection from viral infection or predation by bacteria
Protection from chemicals in environment (e.g., detergents)
Facilitate motility of gliding bacteria
Protection against osmotic stress

92. Pili and Fimbriae Fimbriae (fimbria) Sex pili (pilus)
short, thin, hairlike, proteinaceous appendages
up to 1,000/cell
mediate attachment to surfaces
some (type IV fimbriae) required for twitching motility or gliding motility that occurs in some bacteria
Sex pili (pilus)
similar to fimbriae except longer, thicker, and less numerous (1-10/cell)
required for mating

93. Figure 3.37

94. Flagella and Motility
Figure 3.4

95. Patterns of Flagella Distribution
Monotrichous – one flagellum
Polar flagellum – flagellum at end of cell
Amphitrichous – one flagellum at each end of cell
Lophotrichous – cluster of flagella at one or both ends
Peritrichous – spread over entire surface of cell

96. Flagella Distribution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.38

97. Flagellar Ultrastructure
negatively stained flagella from E. coli; arrows indicate curved hooks and basal bodies
Figure 3.39 (a) and (b)

98. Flagellar Ultrastructure
negatively stained flagella from E. coli; arrows indicate curved hooks and basal bodies
Figure 3.39 (c)

99. The filament
Extends from cell surface to the tip
Hollow, rigid cylinder
Composed of the protein flagellin
Some procaryotes have a sheath around filament

100. The Hook and Basal Body hook basal body links filament to basal body
series of rings that drive flagellar motor
basal body of E. coli flagellum; upper most arrow indicates junction of hook and filament
Figure 3.39d

101. Flagellar Synthesis an example of self-assembly
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Flagellar Synthesis
an example of self-assembly
complex process involving many genes and gene products
new molecules of flagellin are transported through the hollow filament
growth is from tip, not base

102. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Export of flagellar components is carried out by an apparatus in the basal body that appears to be closely related to the type III protein secretion system.
Figure 3.40

103. The Mechanism of Flagellar Movement
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Mechanism of Flagellar Movement
flagellum rotates like a propeller
in general, counterclockwise rotation causes forward motion (run)
in general, clockwise rotation disrupts run causing a tumble (twiddle)

104. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.41

105. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Rotor portion of motor is primarily rod, M ring, and C ring.
Stator portion of motor is Mot A and Mot B.
Figure 3.42

106. Other Types of Motility
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Other Types of Motility
spirochetes
exhibit flexing and spinning movements of axial filaments which are composed of periplasmic flagella
gliding motility
cells coast along solid surfaces
no visible motility structure has been identified

107. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chemotaxis
movement towards a chemical attractant or away from a chemical repellent
concentrations of chemical attractants and chemical repellents detected by chemoreceptors on surfaces of cells

108. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.38: On left is positive chemotaxis by E. coli; outer ring is composed of bacteria consuming serine and the second ring was formed by cells consuming aspaartate, a less powerful attractant; top right colony is composed of motile but nonchemotactic mutant; bottom right colony is composed of nonmotile bacteria.
Figure 3.39: negative chemotaxis by E. coli in response to acetate; bright disks are plugs of agar containing acetate; acetate concentration increases from 0 at the top right to 3 M at top left; as acetate concentration increases, size of bacteria-free zone increases
Figure 3.43
Figure 3.44

109. Chemotaxis Towards Attractant
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chemotaxis Towards Attractant
in presence of attractant (b) tumbling frequency is reduced and runs in direction of attractant are longer
Figure 3.45

110. Chemotaxis away from repellent
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chemotaxis away from repellent
involves similar but opposite responses

111. The Bacterial Endospore
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
The Bacterial Endospore
formed by some bacteria
dormant
resistant to numerous environmental conditions
heat
radiation
chemicals
desiccation

112. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.46

113. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
EX=exosprium
SC=spore coat: composed of several protein layers; impermeable to many toxic molecules; thought to contain enzymes involved in germination
CX=cortex: made of peptidoglycan that is less cross-linked than that in vegetative cells
CW=core wall (spore cell wall)
CR=core: has normal cell structures but is metabolically inactive
Figure 3.47

114. What makes an endospore so resistant?
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
What makes an endospore so resistant?
calcium (complexed with dipicolinic acid)
acid-soluble, DNA-binding proteins
dehydrated core
spore coat
DNA repair enzymes

115. Sporogenesis Also called endospore formation or sporulation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sporogenesis
Also called endospore formation or sporulation
normally commences when growth ceases because of lack of nutrients
complex multistage process

116. Copyright © The McGraw-Hill Companies, Inc
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 3.49

117. Transformation of endospore into vegetative cell
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Transformation of endospore into vegetative cell
germination
complex, multistage process
Clostridium pectinovorum emerging from the spore
Figure 3.50

118. Transformation of dormant spores into active vegetative cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Transformation of dormant spores into active vegetative cells
activation
prepares spores for germination
often results from treatments like heating
germination
spore swelling
rupture of absorption of spore coat
loss of resistance
increased metabolic activity
outgrowth
emergence of vegetative cell