Chapt04 lecture

1. 1
Characteristics of Cells
Eukaryotic cells: animals, plants, fungi, and
protists
– Contain membrane-bound organelles that
compartmentalize the cytoplasm and perform specific
functions
– Contain double-membrane bound nucleus with DNA
chromosomes
Prokaryotic cells: bacteria and archaea
– No nucleus or other membrane-bound organelles

2. 4.3 Prokaryotic Profiles
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3. Figure 4.1 Structure of a bacterial cell
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4. 4
4.3 External Structures
• Appendages
– Two major groups of appendages:
• Motility – flagella and axial filaments (periplasmic
flagella)
• Attachment or channels – fimbriae and pili
• Glycocalyx – surface coating

5. 5
Flagella
• 3 parts:
– Filament – long, thin, helical structure composed of protein
Flagellin
– Hook – curved sheath
– Basal body – stack of rings firmly anchored in cell wall
• Rotates 360o
• Number and arrangement of flagella varies:
– Monotrichous, lophotrichous, amphitrichous, peritrichous
• Functions in motility of cell through environment

6. Figure 4.2 Flagella
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7. 7
Flagellar Arrangements
1. Monotrichous – single flagellum at one end
2. Lophotrichous – small bunches emerging
from the same site
3. Amphitrichous – flagella at both ends of cell
4. Peritrichous – flagella dispersed over surface
of cell; slowest

8. Figure 4.3 Electron micrographs of
flagellar arrangements
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9. 9
Flagellar Responses
Guide bacteria in a direction in response to external
stimulus:
Chemical stimuli – chemotaxis; positive and negative
Light stimuli – phototaxis
Signal sets flagella into rotary motion clockwise or
counterclockwise:
Counterclockwise – results in smooth linear direction –
run
Clockwise – tumbles

10. 10
Fimbriae
• Fine, proteinaceous, hairlike bristles
emerging from the cell surface
• Function in adhesion to other cells and
surfaces

11. 11
Pili
• Rigid tubular structure made of pilin protein
• Found only in gram-negative cells
• Function to join bacterial cells for partial DNA
transfer called conjugation

12. 12
Glycocalyx
• Coating of molecules external to the cell wall,
made of sugars and/or proteins
• Two types:
1. Slime layer - loosely organized and attached
2. Capsule - highly organized, tightly attached
• Functions:
– Protect cells from dehydration and nutrient loss
– Inhibit killing by white blood cells by phagocytosis,
contributing to pathogenicity
– Attachment - formation of biofilms

13. 13

14. 14

15. Figure 4.11 Biofilm on a catheter
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16. Table 4.1 Comparison of Gram-Positive and Gram-Negative
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17. 17
Nontypical Cell Walls
• Some bacterial groups lack typical cell wall
structure, i.e., Mycobacterium and Nocardia
– Gram-positive cell wall structure with lipid
mycolic acid (cord factor)
• Pathogenicity and high degree of resistance to certain
chemicals and dyes
• Basis for acid-fast stain used for diagnosis of infections
caused by these microorganisms
• Some have no cell wall, i.e., Mycoplasma
– Cell wall is stabilized by sterols
– Pleomorphic

18. Figure 4.15 Extreme variation in shape of
Mycoplasma pneumoniae
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19. 19
Cell Membrane Structure
• Phospholipid bilayer with embedded proteins –
fluid mosaic model
• Functions in:
– Providing site for energy reactions, nutrient processing, and
synthesis
– Passage of nutrients into the cell and the discharge of wastes
• Cell membrane is selectively permeable

20. 20
4.5 Bacterial Internal Structures
• Cell cytoplasm:
– Dense gelatinous solution of sugars, amino acids,
and salts
– 70-80% water
• Serves as solvent for materials used in all cell functions

21. 21
• Chromosome
– Single, circular, double-stranded DNA
molecule that contains all the genetic
information required by a cell
– Aggregated in a dense area called the nucleoid
• DNA is tightly coiled
Bacterial Internal Structures

22. Figure 4.17 Chromosome structure
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23. 23
Bacterial Internal Structures
• Plasmids
– Small circular, double-stranded DNA
– Free or integrated into the chromosome
– Duplicated and passed on to offspring
– Not essential to bacterial growth and metabolism
– May encode antibiotic resistance, tolerance to toxic
metals, enzymes, and toxins
– Used in genetic engineering - readily manipulated
and transferred from cell to cell

24. 24
Bacterial Internal Structures
• Ribosomes
– Made of 60% ribosomal RNA and 40% protein
– Consist of two subunits: large and small
– Prokaryotic differ from eukaryotic ribosomes in
size and number of proteins
– Site of protein synthesis
– Present in all cells

25. 25
Bacterial Internal Structures
• Inclusions and granules
– Intracellular storage bodies
– Vary in size, number, and content
– Bacterial cell can use them when environmental
sources are depleted
– Examples: glycogen, poly b-hydroxybutyrate, gas
vesicles for floating, sulfur and phosphate
granules (metachromatic granules), particles of
iron oxide

26. Figure 4.19 Bacterial inclusion bodies
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27. 27
Bacterial Internal Structures
• Endospores
– Inert, resting, cells produced by some G+ genera:
Clostridium, Bacillus, and Sporosarcina
• Have a 2-phase life cycle:
– Vegetative cell – metabolically active and growing
– Endospore – when exposed to adverse environmental conditions;
capable of high resistance and very long-term survival
– Sporulation - formation of endospores
• Hardiest of all life forms
• Withstands extremes in heat, drying, freezing, radiation, and
chemicals
• Not a means of reproduction
– Germination - return to vegetative growth

28. Figure 4.22 Sporulation cycle
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29. 29
Endospores
• Resistance linked to high levels of calcium and
dipicolinic acid
• Dehydrated, metabolically inactive
• Thick coat
• Longevity verges on immortality, 250 million
years
• Resistant to ordinary cleaning methods and boiling
• Pressurized steam at 120oC for 20-30 minutes will
destroy

30. 30
4.6 Bacterial Shapes,
Arrangements, and Sizes
• Vary in shape, size, and arrangement but
typically described by one of three basic
shapes:
– Coccus – spherical
– Bacillus – rod
• Coccobacillus – very short and plump
• Vibrio – gently curved
– Spirillum – helical, comma, twisted rod,
• Spirochete – spring-like

31. Figure 4.23 Common bacterial shapes
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