prof . dr. ihsan edan alsaimary department of microbiology - college of medicine - university of basrah - basrah -IRAQ ihsanalsaimary@gmail.com 00964 7801410838

1. Bacterial Cell Structure
and Function
Prepared by
Prof dr. Ihsan Edan Alsaimary
department of microbiology – college of medicine – university of basrah
Mobile : 07801410838
- e.mail : ihsanalsaimary@gmail.com

2. Size of Living Things
1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm
1mm = 1000 µm = 1000000nm
1 µm = 1000nm

3. 3

4. 4
Shapes Are Used to Classify
• Bacillus: Rod shaped
• Coccus: Spherical
(round)
• Vibrio: Comma
shaped with flagella
• Spirillum: Spiral
shape
• Spirochete: wormlike
spiral shape

5. 5
Cellular organism copies it’s genetic information
then splits into two identical daughter cells

6. 6
Overview of
prokaryotic cell.

7. Cell membranes
Why study bacterial cell membranes?
• They are essential structures in bacteria.
• They are made of chemical components
found nowhere else in nature.
• They may cause symptoms of disease in
animals.
• They are the site of action of some of our
most important antibiotics.

8. Profile of the bacterial cell envelope
• Gram-positive cell membranes is thick
homogeneous monolayer
• Gram-negative cell membranes is thin
heterogeneous multilayer

9. Primary function of the bacterial cell
membranes
• To prevent rupture or
osmotic lysis of the cell
protoplast
• Where bacteria treated with
detergent:
• Protoplast
• Spheroplast
• L-form bacteria
Lysis of a pair of dividing E. coli cells

10. Prokaryotes - Cell Wall
Gram-Positive & Gram-Negative

11. Microbiology – Chapter 4, Bacteria
• Grams stain = a differential stain procedure, different results, + and
(-)

12. Chemical nature of bacterial cell
membranes
Peptidoglycan is made up of
• 2 amino sugars
N-acetyl-glucosamine = G
N- acetylmuramic acid = M
• 4 amino acids
L-alanine = L-ala
D-glutamic acid = D-glu
diaminopimelic acid = DAP
D-alanine = D-ala

13. 13
Function and Structure of
peptidoglycan
• Provides shape and structural support to cell
• Resists damage due to osmotic pressure
• Provides some degree of resistance to diffusion
of molecules
• Single bag-like, seamless molecule
• Composed of polysaccharide chains cross
linked with short chains of amino acids:
“peptido” and “glycan”.

14. Chemical nature of bacterial cell membranes
Gram-positive and negative murein showing the sites of
action of the antibiotic penicillin and the enzyme
lysozyme
Penicillin prevents
formation of this
Interpeptide bond
Lysozyme breaks this
glycoside bond between
M and G

15. Outer membrane of Gram-negatives has two important
properties
1. It protects the cells from permeability by many
substances including penicillin and lysozyme.
2. It is the location of lipopolysaccharide (endotoxin) which
is toxic for animals.

16. • Gram + only
• Glycerol, Phosphates, & Ribitol
• Attachment for Phages
• Participate in MG supply to the cell
• Antigenic determinant
Teichoic Acids

17. 17
Teichoic acid and lipoteichoic
acid Found in Gr+ cell
wall

18. 18
Teichoic acid and lipoteichoic acid
Structure and Function
•Polymer of phosphate and ribitol or glycerol
R: sugar or amino acid
•Lipoteichoic acid covalently attached to
membrane lipids.
•Major contributor to negative charge of cell
exterior.
•Appears to function in Ca++ binding
•May be associated with adherence on
smooth surface Strept mutans tooth decay
•May be part of slim layer Ps.aeruginosa

19. Lipopolysaccharide (LPS)
• Endotoxin or Pyrogen
– Fever causing
– Toxin nomenclature
• Endo- part of bacteria
• Exo- excreted into environment
• Structure
– Lipid A
– Polysaccharide
• O Antigen of E. coli, Salmonella
• G- bacteria only
– Alcohol/Acetone removes primary stain
durind gram’s staining.

20. Table: Correlation of the Gram stain with
properties of bacterial cell walls
Property Gram-positive Gram-negative
Thickness of membranes thick (20-80 nm) thin (10 nm)
Number of layers 1 2-3
Peptidoglycan
(murein) content
>50% 10-20%
Teichoic acids in membranes present absent
Protein/lipoprotein
content
0-3% >50%
Lipopolysaccharide
content
0 13
Sensitivity to penicillin sensitive resistant
Sensitivity to lysozyme sensitive resistant

21. 21
Cell membrane Exceptions
• Mycobacterium and relatives
– Wall contains lots of waxy mycolic acids
– Attached covalently to PG
• Mycoplasma: no cell membranes
– Parasites of animals, little osmotic stress
• Archaea, the 3rd domain
– Pseudomurein and other chemically different
membranes materials (murein another name for
PG)

22. Plasma Membrane
 Separates the cell from its environment.
 Limits the protoplast
 Thin n elastic , can be only seen with electron microscope
 With the exception of mycoplasma , bacterial cytoplasmic memb.lacks
sterol.
 Phospholipid molecules oriented so that hydrophilic,water-loving
heads directed outward and hydrophobic ,water-hating tails directed
inward.
 Proteins embedded in two layers of lipids (lipid bilayayer)
FUNCTIONS:
Semipermeable membrane
 Housing enzymes for cell wall, outer membrane synthesis, assembly n
secretion of extractoplasmic n extracellular substances
 Generation of ATP
 Cell motility
 Mediation of chromosomal segragation during replication

23. Membrane structure and assembly
• The
membrane
bilayer is
formed by
phospholipid
molecules
made up of
glycerol and
fatty acids

24. The procaryotic ribosome (L) is 70S in size, being
composed of a 50S (large) subunit and a and 30S (small)
subunit. The eucaryotic ribosome (R) is 80S in size and is
composed of a 60S and a 40S subunit.
Ribosome Structure and Composition

25. Inclusion Composition
Glycogen poly-glucose Reserve carbon and
energy source
Poly-betahydroxybutyric
acid (PHB)
lipid Reserve carbon and
energy source
Poly-phosphates polymers of PO4 Reserve phosphate,
possibly high-energy PO4
Sulfur globules elemental S Reserve energy and or
electrons
Magnetosomes magnetite (iron oxide) Provide orientation in
magnetic field
Gas vesicles protein shells inflated with
gases
Provide buoyancy in
aquatic environments
Parasporal crystals protein Produced by endospore-
forming Bacilli - toxic to
insects
Function
Some inclusions in Bacterial Cells

26. Endospores are produced as intracellular structures within the cytoplasm
of certain bacteria, most notably Bacillus and Clostridium species.
Endospore forming bacteria left to right: Clostridium botulinum, Bacillus brevis, Bacillus thuringiensis

27. Medically-important
Endospore-forming Bacteria
• Bacillus anthracis causes anthrax
• Bacillus cereus causes food poisoning
• Clostridium tetani causes tetanus
• Clostridium botulinum causes botulism
• Clostridium perfringens causes food
poisoning and gas gangrene
• Clostridium difficile causes antibiotic-induced
diarrhea and pseudomembranous colitis

28. 28
Flagella
• Bacteria that are motile have appendages
called flagella
• Attached by Basal Body
• A bacteria can have one or many flagella

29. 29
• Made of Flagellin
• Used for Classification
• Monotrichous: 1 flagella
• Lophotrichous: tuft at one end
• Amphitrichous: tuft at both ends
• Peritrichous: all around bacteria

30. 30
Pili (fimbriae)
• Short protein
appendages
• Smaller than flagella
• Adhere bacteria to
surfaces(host epithelium)
• Used in conjugation for
Exchange of genetic
information
• Aid Flotation by
increasing buoyancy

31. •capsule
• Glycocalyx – sugar coat irregular seceretion of
polysaccharides,
• capsule : tightly bound regular distribution
– Protects and prevents from drying, also protects from
phagocytes
*Slim layer: thin secretion of polysaccharides, and often a
significant component of “biofilms”

32. Prokaryotes - Glycocalyx
2.Polysaccharides firmly attached
to the cell wall.
 Capsules adhere to solid
surfaces and to nutrients in the
environment.
 Adhesive power of capsules is a
major factor in the initiation of
some bacterial diseases.
 Capsule also protect bacteria
from being phagocitized by cells
of the hosts immune system.

33. 33
• Plasmids
• Extra-chromosomal circular DNA
• multiple copy number
• coding
- pathogenesis factors
- antibiotic resistance factors
• bacterial replication