Functional anatomy prokaryotic cell structure

1. z
STRUCTURE OF
PROKARYOTIC CELL
Dr. Pulipati Sowjanya
Associate Professor
Vignan Pharmacy College
Guntur

2. z
Contents
Appendages-
flagella, pili, fimbrae
Cell envelope-
glycocalyx, cell wall, cell membrane
Cytoplasm-
ribosomes, granules, nucleoid/chromosome.

3. Prokaryote Eukaryote

4. z
Prokaryotes Vs Eukaryotes

5. Shapes and Arrangement of Bacteria

6. zChemical Composition of Bacteria
•
•
Water - 70%
Dry weight - 30% composed of:
–
–
–
•
•
•
•
–
–
–
DNA - 5% MW 2,000,000,000
RNA - 12%
protein- 70% found in:
Ribosomes(10,000) – RNA
Protein particles - MW 3,000,000
Enzymes
Surface structures
polysaccharides - 5%
lipids - 6%
phospholipids - 4%

7. z Prokaryote Cell Structure
1. Appendages- flagella, pili/fimbrae
2. Cell envelope- glycocalyx, cell wall ,
cell membrane
3. Cytoplasm- ribosomes, granules,
nucleoid/chromosome.

8. z
Bacterial Appendages
• Pili (pl), pilus (s)
–
–
only found in gram negative bacteria
tubulare, hairlike structures of protein larger
and more rare than fimbriae.
•
-
-
2 types of pili
attachment pilus - allow bacteria to attach to
other cells/ solid surfaces
sex pilus, - transfer from one bacterial cell to
another- conjugation.

9. z Fimbriae
• fimbriae (pl) fimbria (s)
– Adhesion to cells and surfaces
– Responsible for biofilms.
Escherichia coli

10. Comparison of Pili & Fimbriae

11. z Flagella
• Flagella (pl), flagellum(s)
– long appendages which rotate by means of a "motor" located
just under the cytoplasmic membrane.
– bacteria may have one, a few, or many flagella in different
positions on the cell.
• Advantages
- chemotaxis - positive and negative.
- motility
• All spirilla, half of bacilli, rare cocci.

12. z
Flagella

13. z
Flagella
Three morphological regions
•
–
–
Helical filament
long outermost region; composes up to 90% of its length
contains the globular (roughly spherical) protein flagellin
arranged in several chains and form a helix around a hollow
core
–
• Hooked or curved area
filament is attached; consists of a different protein
•
–
–
–
Basal body
terminal portion of the flagellum
fix the flagellum to the cell wall and plasma membrane
composed of a central rod inserted into a series of rings
Gram negative - 2 pairs of rings
•
•
Outer pair - fixed to the outer membrane and peptidoglycan
layer
Inner pair - fixed to the plasma membrane (SM ring)
Gram positive - only inner pair is present

14. z Types of Flagellar Arrangements

15. z
Motility
•
–
–
–
Types of bacterial motility
run or swim - when a bacterium moves in one direction
for a length of time
tumbles - periodic, abrupt random changes in direction
swarming - rapid wavelike growth across a solid culture
medium
• Mechanism of flagellar movement - relative
rotation of the rings in the basal body of the
flagellum
Antigenicity
– flagellar or H antigen - useful in the serological
identification of serotypes of Salmonella organisms

16. z
Flagellar Movement
Doetsch & Sjoblad described
flagellar movement that
flagella function as a
propeller of a boat.
If the rotation of flagella is in
anti clock-wise direction, the
bacterial cell moves in clock –
wise direction.

17. z
Spirochetal Movement
Tuft of axial fibrils/ endoflagella that
arise at the ends of the cell under
the outer membrane and spiral
around the cell
Found in Spirochetes and are
similar to flagella, but are located
between the cell wall and an outer
membrane, and are attached to
one end of the organism.
Gliding Movement
Some bacteria like cyanobacteria &
mycoplasmas show gliding
movement when come in contact
with solid surface

18. z
Motility of Bacteria
Two ways by which motility can be demonstrated:
• direct or microscopic
– hanging drop preparation or wet mount preparation by dark field
mycroscope
– Distinguishes:
• Brownian movement - when the bacteria show molecular movement
• true motility - if a bacterium describes a rotatory, undulatory or
sinuous movement
• indirect or macroscopic
– Stab inoculation of the semisolid media
• nonmotile - growth is limited at the point of inoculation
• motile - growth is diffuse or moves away from the line of inoculation;
turbidity of the medium

19. z
Detection of Motility
• Direct • Indirect
Presence mobile bacteria

20. z Taxis
Chemotaxis:
Movement of bacteria towards
chemical attractant and away
from repellant
Aerotaxis:
Movement of bacteria based on requirement of aeration.
Aerobic
Anaerobic
Microaerophilic

21. z Taxis
Phototaxis:
Phototaxis is the movement of an organism in response to light: that is, the
response to variation in light intensity and direction.
Negative phototaxis, or movement away from a light source.
Positive phototaxis, or movement towards a light source, is advantageous
for phototrophic organisms as they can orient themselves most efficiently
to receive light for photosynthesis.
Many phytoflagellates, e.g. Euglena, and the chloroplasts of higher plants
positively phototactic, moving towards a light source.

22. z Taxis
Magnetotaxis:
Magnetotaxis is the movement of an organism towards or away from
magnetic field.
Magnetotactic bacteria possess a chain of magnetite (Fe2O4) particles
known as magnetosomes.
Figure: Aquaspirillum magnetotacticum

23. z
2. Bacterial Surface Structure
- cell envelope
A. Glycocalyx - some extracellular material
secreted by many bacterial cells in the form of:
a. capsule - attached tightly to the bacterium and has
definite boundaries.
b. slime layer - loosely associated with the bacterium
and can be easily washed off
Compositions:
-
-
layer of polysaccharide
proteins - sometimes

24. Differences between Capsule and Slime Layer

25. z
Functions of the Capsule
• Protection
• Identification
• Vaccine preparation
• Tissue attachment

26. z Medical Importance
rapid serological identification of:
• Several groups of streptococci
• Meningococcus
• Hemophilus influenzae
• Klebsiella pneumoniae
• Yersinia and Bacillus species

27. z
Functions of the Capsule
• Protection
• Identification
• Vaccine preparation
• Tissue attachment
• Antibiotic barrier

28. z
Cell wall
Peptidoglycan (polysaccharides +
protein),
• Support and shape of a bacterial cell.
The three primary shapes in
bacteria are:
• coccus (spherical),
•
•
•
bacillus (rod-shaped)
spirillum (spiral).
Mycoplasma are bacteria that
have no cell wall and therefore
have no definite shape.

29. z
Cell wall
peptidoglycan (polysaccharides + protein)
Components of the peptidoglycan layer:
Repeating glycan chains - N acetyl
glucosamine (NAG) and N acetyl muramic acid
(NAM) joined with 1,4 – glycosidic bond.
A set of identical tetrapeptide side
chains attached to N- acetylmuramic
acid
A set of identical peptide cross bridges

30. z
Peptidoglycan

31. z
Differences in Cell Wall Structure
• Basis of Gram Stain Reaction
– Hans Christian Gram- 1884
• Differential Stain
– Gram Positive vs Gram Negative Cells
• Gram Positive Cells-
– Thick peptidoglycan layer with embedded teichoic
acids
• Gram Negative Cells-
– Thin peptidoglycan layer, outer membrane of
lipopolysaccharide.

32. z Gram Positive Cell Wall
• Multilayered peptidoglycan covered
by surface layer (S-layer).
• Teichoic acid – ribitol phosphate or
glycerol phosphate.
• Teichuronic acid – long chains of
alternating glucuronic acid and N-
acetylgalactosamine linked with 1-3
glycosidic bond.
• Lipoteichoic acid – teichoic acid
originated from cell membrane.

33. Gram Positive Cell Wall
• The peptidoglycan chains
contains tetrapeptides
consisting L-lysine-D-
alanine-L-lysine-D-alanine
residues.
• In some members like
Staphylococcus aureus
the tetrapeptide chain is
connected through
pentaglycine chains. Fig.: Organisation of peptidoglycan layer of Staphylococcus aureus.
1. L-lysine, 2. D-alanine, 3. L-lysine, 4. D-alanine, G-glycine

34. Acid fast bacteria
• M. tuberculae & M. leprae show the property of acid
fastness.
• When these bacteria are stained with carbol-fuchsin and
then washed with dilute acid, the bacteria retain the stain.
• Non- acid fast organisms destained by this treatment.
• The acid fastness property was found to be due to the
presence of mycolic acid lipid in cell walls.

35. z Gram Negative Cell Wall

36. Gram Negative Cell Wall
• The distinctive feature of Gram-ve cell wall is
the presence of an outer membrane.
• Presence of few layers of peptidoglycan layer.
• Peptidoglycan is present in periplasmic space
and covalently linked with lipoproteins in the
outer membrane.
• Teichoic acid or teichuronic acid chains are
absent.
• Outer membrane is a bilayered structure
composed of lipopolysaccharides, lipoproteins
& phospholipids.

37. Gram Negative Cell Wall
• The lipopolysaccharides has 3 components –
Lipid A embedded in the outer membrane,
core polysaccharide lying on the membrane
surface and polysaccharide side chains (O-
antigen) projecting outside the membrane.
• Outer membrane possess pores contains a
special protein porin.
• These pores allow the entry of molecules into
the cytoplasm
• Outer membrane – several proteins
• Receptor protein – entire outer membrane
• Braun’s protein – restricted to the inner layer.

38. Gram Negative Cell Wall
• The peptidoglycan layer of Gram –ve bacterial cell wall
contains tetrapeptide chain contains meso-diaminopimelic
acid (m-DAP) in place of L-lysine and pentaglycine chain is
absent.
• The tetrapeptide chains are directly cross linked between m-
DAP & D-alanine of adjacent peptidoglycan chains.
• The outer membrane protects the bacteria from the action of
lysozyme.
• Lysozyme present in saliva, tears and other body fluids. It
breaks the glycosidic bond between NAG & NAM.

39. Differential Response to Gram Stain
• The crystal-violet iodine complex is
deposited on the cytoplasmic
membrane.
• Washing with alcohol removes the
stain in Gram-ve bacteria, because of
thin layer of peptidoglycan.
• Gram+ve bacteria contains thick
layer of peptidoglycan, hence it
retains crystal violet stain.

40. Functions of Cell Wall
 Maintenance of the shape (due to rigidity of peptidoglycan).
Protects the cytoplasmic membrane cell contents
Rigidity
Cell wall is osmotically insensitive
Hypotonic solution – cell burst.
Hypertonic solution – cell shrank.
Isotonic solution – bacteria is life.
 It acts as barrier for diffusion to certain molecules.
 The O-antigen determines the antigen specificity of Gram negative
bacteria.

41. z Cytoplasmic Membrane
 Phospholipid bilayer
 “Fluid mosaic” model
 Embedded proteins for active transport
 Enzymes for energy generation
 Photosynthetic pigments

42. z Cell membrane
 General structure is phospholipid bilayer Contain both
hydrophobic and hydrophilic components.
 Fatty acids point inward to form hydrophobic
environment; hydrophilic portions remain exposed to
external environment or the cytoplasm

43. z
Cell membrane
Peripheral
Membrane
Protein
Integral
Membrane
Protein
Peripheral
Membrane
Protein
Phospholipid

44. Phospholipid Bilayer Membrane

45. z Cell membrane
Two types of proteins
 Peripheral- are loosely associated to the membrane and
can be easily separated. Generally they make up
between 20 and 30% of the total membrane proteins
 Integral proteins- are amphipathic like the lipids, much
more strongly associated to the membrane, and make up
about 70 to 80% of total proteins

46. z
Cell membrane
Figure: Presence of steroids in
plasma membrane (A) and chemical
structure of a steroid (B)
In some microorganisms such as
mycoplasmas & fungi, sterols are
found to be associated within the
plasma membrane.
The sterols are structurally
different from the lipids.

47. z
 Selective permeability to different molecules.
 Active transport aided by permease.
 Play a role in DNA replication.
 Cell wall biosynthesis.
 Mesosomes ----- cell division.
Function of Cytoplasmic Membrane

48. z
Mesosomes
Figure: The bacterial mesosome
Mesosomes are invaginated structures formed
by infoldings of inner membrane of plasma
membrane.
Salton & Owen suggested that the
mesosomes are formed due to
vesicularization of outer half of the lipid
bilayer.
Functions:
 Their exact function is unknown but they are supposed to take part in
respiration.
 They play an important role in cell division.
 Mesosomes begin the formation of septum and attach the bacterial
DNA to the cell membrane.

49. z
CYTOPLASM
Ribosomes:
 Thousands of ribosomes are present that gives granular appearance
of the cytoplasm.
 During protein synthesis ribosomes form a chain connected by the
m-RNA, such strings of ribosomes are known as polysomes.
Figure: The prokaryotic ribosome. (a) A small 30S subunit and
(b) a large 50S subunit © the complete 70S prokaryotic ribosome

50. z CYTOPLASM
Bacterial Nucleus (Nucleoid):
 It consists of single, long supercoiled,
circular, dsDNA molecule which is
associated with RNA and some
proteins.
 The supercoiling is induced by
topoisomerase enzyme
Figure: The process of folding and super
coiling of bacterial chromosome

51. z
CYTOPLASM
Cytoplasmic inclusions:
 Volutin granules: insoluble polyphosphates – source of reserve phosphate.
 Polymer of β-hydroxybutyric acid (PHB): a fat substance – source of
carbon & energy.
 Sulphur granules: found in photosynthetic bacteria
 Parasporal body: possess insecticidal property
Ex: Bacillus thuringiensis Figure: Sulphur granules found
in Chromatium vinosum

52. z
CYTOPLASM
Magnetosomes:
 Magnetotaxis is the movement of an organism towards or away
from magnetic field.
 Magnetotactic bacteria possess a chain of magnetite (Fe2O4)
particles known as magnetosomes.
Figure: Aquaspirillum magnetotacticum

53. z Endospores
The spore is externally covered by a loose
structure called exosporium which is
formed by the remnants of mother cell
protoplast.
Inside the exosporium several layers of
spore coats are present. Next to the coat
layers a thick zone called cortex is
present. Below the cortex lies the
primordial cell wall enclosing the inner
membrane. The inner membrane
surrounds the core protoplast of the
spore

54. Endospore Formation

55. z Endospore Formation
 Endospore is formed by accumulation of Ca++ in the mother cell.
 In vegetative cells, Ca++ level is low but during sporulation, Ca++ is
actively transported from the medium.
 From the mother cell cytoplasm, Ca++ is transported by facilitated
diffusion into the forespore.
 The forespore contains dipicolinic acid and it forms calcium
dipicolinate complex.
 The concentration of calcium dipicolinate is high and it results in heat
resistance of the bacterial endospores.

56. z Exospore Formation
 Cells of methane-oxidizing genus Methylosinus forms exospores
i.e., spores external to the vegetative cells by budding at one end of
the cell.
 These are desiccation and heat resistant but they do not contain
dipicolinic acid.
 Examples of exospores include Conidiospores, streptomyces,
actinobacteria and diverse groups of fungi, algae and
Cyanobacteria.

57. Streptomyces MicrobisporaMicromonospora
Conidia are formed externally and found in most species of
Actinomycetes.
In Streptomyces, Micromonospora, Microbispora conidia are formed
in the aerial hyphae.
The conidia are long, straight, spiral or coiled chains of conidia
formed from the tip of conidiophores.
Exospore Formation

58. z REFERENCES
1. Prescott, Harley and Klein's, Microbiology. 5th edition. 42-72.
2. Gerard J. Tortora, Berdell R. Funke, Christine L. Case. Microbiology
– An Introduction. 10th edition. Pearson. 76-97.
3. Michael J. Pelczar, JR., E.C.S. Chan, Noel R. Krieg. Microbiology.
5th edition. 73-97.

59. z
It is easy to solve a problem that everyone sees, but it’s
hard to solve a problem that no one sees