1. Cell Structure and Function
Chapter 4/5
Cell Structure and Function

2. Cell Structure and Function
Topics
External Structures
Cell Envelope
Internal Structures
Cell Shapes, Arrangement, and Sizes
Classification

3. An Infectious Exam Patient with Tuberculosis Ziehl Neelson stain
Mycobacterium tuberculosis its function is a factor of its structure
Thick waxy outer covering
Doesn’t stain normally
Grows slowly, resides in macrophages
Drug sensitivity

4. The Prokaryotic cell
So different from the cell you’re used to studying! (Eukaryotic cells)
No membrane bound organelles
Unbound DNA instead of a membrane bound nucleus
Cell wall made of peptidoglycan
Smaller than a eukaryotic cell
Nutrient entrance rate
Surface to volume ratio

6. Bacterial cell structure
The prokaryotic cell from the inside out has 3 basic parts:
Cytoplasm; fills the cell and houses the internal structures.
The “envelope” which is a general term to refer to the cell wall and membrane.
“Accessories” fun extras that not all bacteria have.

8. Figure 3.2 Typical prokaryotic cell
Inclusions
Ribosome
Cytoplasm
Nucleoid
Flagellum
Glycocalyx
Cell wall
Cytoplasmic membrane

9. Cytoplasm Made of water and protein, metabolism occurs here.
The nucleoid region 
Circular loop of naked DNA.
Plasmids.
Ribosomes
Protein factories
Different from our own
Inclusions- other visible structures
Storage granules
vacuoles

10. The “envelope”
The envelope serves as the cell boundary and discerning gateway.
The envelope can have up 3 layers, depending on what type of cell it is.
1. Outer membrane
2. Cell wall
3. Cytoplasmic
membrane

11. Cell wall Gram positive cell wall Gram-negative cell wall
Thick peptidoglycan (PG) layer
Acidic polysaccharides
Teichoic acid and lipoteichoic acid
Gram-negative cell wall
Thin PG layer
Outer membrane
Lipid polysaccharide
Porins

12. Gram-negative cell Contains all 3 layers
Outer membrane is a bilayer. Lipopolysaccharide (LPS) layer toward the outside, and a phospholipid layer toward the inside, with proteins through out. Layer is attached to the cell wall by lipoproteins.
Useful as protection
Is a toxin to mammals

13. Gram positive cell Have teichoic acids sprinkled through out
the cell wall, increases integrity of wall
Cell wall is very thick compared to gram negative cells
Does not have the LPS layer
Does not have periplasm

14. Mycoplasma bacteria have no cell wall, which contributes to varied shapes.
Fig Scanning electron micrograph of Mycoplasma pneumoniae

15. Periplasmic space, or periplasm- space between the outer membrane and the cytoplasmic membrane. Houses the cell wall as well as binding proteins and enzymes.

16. Cell wall In general a. made of unique material peptidoglycan (murein)
b. Site of some antibiotic action (Penicillin stops cell wall formation)
c. Cell wall is rigid & determines shape
d. Cell wall is porous like a woven basket. Has great strength, but openings.
e. Keeps cell from bursting under normal circumstances (turgor pressure)
f. Reason for staining differences

18. Structure of wall Glycan part (polysaccharide) made
of long chains of two alternating
sugars
N-acetlyglucosamine (NAG)
N-acetylmuramic acid (NAM)
Encircle the cell like hoops on a barrel
Held together or cross linked with the ‘peptido’ part (protein) attached to NAM’s only.
Protein differs between bacterial species

19. Reason for staining differences

20. Cell Membrane Phospholipid bilayer (+ proteins)
-Phosphate group (polar, water loving)
-Fatty acids (nonpolar, water phobic)
-Remember your integral proteins!
receptor sites, enzymes, transport proteins.
* no cholesterol in prokaryotic membranes
Cell membrane is the site of chemiosmosis to make ATP

22. Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer
Head, which contains phosphate (hydrophilic)
Phospholipid
Tail (hydrophobic)
Integral proteins
Cytoplasm
Integral protein
Phospholipid bilayer
Peripheral protein
Integral protein

23. Bacterial Cytoplasmic Membranes
Function
Passive processes
Diffusion
Facilitated diffusion
Osmosis
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24. Diffusion through the phospholipid bilayer
Figure Passive processes of movement across a cytoplasmic membrane-overview
Extracellular fluid
Cytoplasm
Diffusion through the phospholipid bilayer
Facilitated diffusion through a nonspecific channel protein
Facilitated diffusion through a permease specific for one chemical; binding of substrate causes shape change in the channel protein
Osmosis, the diffusion of water through a specific channel protein or through the phospholipid bilayer

25. Bacterial Cytoplasmic Membranes
Function
Active processes
Active transport
Group translocation
Substance chemically modified during transport
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26. Pili and fimbriae
Attachment
Mating (Conjugation)

27. Accessory structures Appendages Fimbriae Pili and/or flagella
Hair like appendages (not cilia)
Protein projections that extend all the way from the membrane.
Used for attachment, adhesins.
S. mutans & teeth, or mucous membranes such as urethra.

28. Figure Fimbriae
Flagellum
Fimbria

29. Pili Special type of fimbria Also known as conjugation pili
Longer than other fimbriae but shorter than flagella
Bacteria typically have only one or two per cell
Mediate the transfer of DNA from one cell to another (conjugation)
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30. Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another.
Fig. 4.8 Three bacteria in the process of conjugating

31. Figure Pili
Conjugation pilus

32. Flagella Some bacteria don’t move, others move with flagella.
Structure is very different from eukaryotic flagella.
Made of protein flagellin
Propeller action vs. wavelike action
No 9+2 micro tubular arrangement
Prokaryotic
Eukaryotic

33. Figure 3.6 Proximal structure of bacterial flagella-overview
Filament H o k
Direction of rotation during run
Rod
Peptidoglycan layer (cell wall)
Protein rings
Cytoplasmic membrane
Cytoplasm
Filament H o k
Outer protein rings
Outer membrane
Rod
Cell wall
Gram 
Gram 
Peptidoglycan layer
Basal body
Integral protein
Inner protein rings
Cytoplasmic membrane
Cytoplasm
Integral protein

34. Process of Movement (Run and Tumble method)
1. Taxis – the movement of a bacterium toward or away from a particular stimulus.
Toward (+), away (–)
Examples:
Chemotaxis
Aerotaxis
Phototaxis

36. Number/location of flagella are distinguishing characters
1. One flagella = monotrichous
2. Cluster at one end = lophotrichous
3. both ends = amphitrichous
4. Covering the cell = peritrichous

37. Glycocalyx Capsule Slime layer Protects bacteria from immune cells
Enable attachment and aggregation of bacterial cells

38. Glycocalyx/Capsule/Slime layer
Not on all bacterial cells but if present it’s the outermost layer.
Capsule – tends to be thick, rigid and smooth.
Slime layer – is thinner & less rigid, globular
*Extra layer guards against desiccation
*Protects the cell from phagocytosis
(S. pneumoniae)
*Can be used as attachment such
as in tooth decay bacteria (S. mutans)

39. Figure 3.5 Glycocalyces-overview
Glycocalyx (capsule)
Glycocalyx (slime layer)

40. The slime layer is associated with the formation of biofilms, which are typically found on teeth.
Fig Biofilm

42. During nutrient depleted conditions, some bacteria (vegetative cell) form into an endospore in order to survive.
Fig Microscopic picture of an endospore formation

43. Survival Structures A. Endospores (sporogenesis)
1. Made when the environment goes “bad”
2. Endospore contains all the important parts of the cell.
3. Only made by certain bacteria
(Bacillus and Clostridium)
4. Not reproduction!! No increase in #’s
5. Autoclaving is the only way to destroy
spores. 121 Celsius/15-20lbs.
per square inch/15-20 min.

44. Figure 3.24 The formation of an endospore-overview
Cytoplasmic membrane
Cell wall
DNA is replicated.
A cortex of calcium and dipicolinic acid is deposited between the membranes.
Cortex
DNA
Vegetative cell
Spore coat forms around endospore.
Spore coat
DNA aligns along the cell’s long axis.
Outer spore coat
Endospore matures: completion of spore coat and increase in resistance to heat and chemicals by unknown process.
Cytoplasmic membrane invaginates to form forespore.
Forespore
Endospore
Outer spore coat
Endospore is released from original cell.
Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell’s DNA disintegrates.
First membrane
Second membrane

45. Clostridium tetani

46. Cell shapes Coccus Rod or bacillus Curved or spiral Cell arrangements
Cell size

47. Cell arrangements Single – cells found by themselves.
Diplo - cells in pairs. Diplococcus, Diplobacillus
Strepto – cells in chains. Streptococcus,
Streptobacillus
Staphylo – cells in grape like clusters.
Staphylococcus

50. Classification Phenotypic methods Molecular methods Taxonomic scheme
Unique groups

51. Phenotypic methods Cell morphology -staining
Biochemical test – enzyme test

52. Molecular methods
DNA sequence
16S RNA
Protein sequence

53. The methods of classification have allowed bacteria to be grouped into different divisions and classes.
Table 4.3 Major taxonomic groups of bacteria

54. An example of how medically important families and genera of bacterial are characterized.
Table 4.4 Medically important families and genera of bacteria.