This document discusses the structure of bacteria. It begins by comparing prokaryotes and eukaryotes, noting key differences such as DNA location, organelles, and ribosomes. It then describes bacteria specifically, including their size, shapes, structures like flagella and cell walls, and differences between gram positive and gram negative bacteria. Important bacterial components are also outlined, such as peptidoglycan, teichoic acids, lipopolysaccharides, and endospores.

1. Structure Of
Bacteria
Maj M. Omair Riaz
Assistant Professor of Pathology
QIMS

2. Difference Between Prokaryotes
and Eukaryotes
Prokaryotes
 DNA not within nuclear membrane
 No mitotic division
 DNA not associated with histones
 Single chromosome
 No Membrane bound organelles
 70S Ribosome
 Cell wall with peptidoglycan
 Examples: Bacteria
Eukaryotes
 DNA within nuclear membrane
 Mitotic division present
 DNA associated with histones
 More than one chromosome
 Membrane bound organelles
present
 80S Ribosome
 No cell wall with peptidoglycan
 Examples: Fungi & protozoa

4. Bacteria
 Are Prokaryote cells
 Contain both DNA and RNA
 Divide by Binary Fission
 Have a cell wall
 Cell wall differs in Gram positive and Gram
negative organisms
 Nomenclature is Binomial e.g. Escherichia coli.

5. Bacteria
 Size Range 0.2 – 5 um
 The smallest bacteria are Mycoplasma and they
are the same size as the largest viruses i.e.
poxviruses.
 The longest bacteria (rods) approach the size of
some yeasts and human red blood cells

6. Shapes of Bacteria
 Coccus
 Cluster - Staphylococcus
 Chain - Streptococcus
 Bacillus
 Coccobacillus
 Vibrio (Curved Rod)
 Spiral (Spirochete)

7. Basic Shapes

9. Bacterial Structures
 Flagella
 Pili
 Capsule
 Plasma Membrane
 Cytoplasm
 Cell Wall
 Lipopolysaccharides
 Teichoic Acids
 Inclusions
 Spores

10. Flagella
 Motility - movement
 Swarming occurs with some bacteria
 Spread across Petri Dish
 Proteus species most evident
 Arrangement basis for classification
 Monotrichous; 1 flagella
 Lophotrichous; tuft at one end
 Amphitrichous; both ends
 Peritrichous; all around bacteria

12. Pili
 Short protein appendages
 smaller than flagella
 Adhere bacteria to surfaces
 E. coli has numerous types
 F-pilus; used in conjugation
 Exchange of genetic information
 Flotation; increase boyancy

14. Capsule or Slime Layer
 Glycocalyx - Polysaccharide on external
surface
 Adhere bacteria to surface
 S. mutans and enamel of teeth
 Prevents Phagocytosis
 Complement can’t penetrate sugars

15. Cytoplasm
 80% Water {20% Salts-Proteins)
 DNA is circular, Haploid
 Plasmids; extra chromosomal DNA
 Antibiotic Resistance
 No organelles (Mitochondria, Golgi, etc.)

16. Cell Membrane
 Bilayer Phospholipid
 Water can penetrate
 Flexible
 Not strong, ruptures easily
 Osmotic Pressure created by cytoplasm

18. Cell Wall
 Peptido-glycan Polymer (amino acids +
sugars)
 Unique to bacteria
 Sugars; NAG & NAM
 N-acetylglucosamine
 N-acetymuramic acid
 Amino acids cross link NAG & NAM

19. Cell Wall Summary
 Determine shape of bacteria
 Strength prevents osmotic rupture
 20-40% of bacteria
 Unique to bacteria
 Some antibiotics effect directly
 Penicillin

20. Gram Positive vs Gram Negative
Gram Positive
 Thick Peptidoglycan layer
 Teichoic acid present
 Lipopolysaccharide
absent
 Outer membrane absent
 Periplasmic space absent
Gram Negative
 Thin Peptidoglycan layer
 Teichoic acid absent
 Lipopolysaccharide
present
 Outer membrane present
 Periplasmic space present

21. Teichoic Acids
 Gram + only
 Glycerol, Phosphates, & Ribitol
 Attachment for Phages

23. Lipopolysaccharide (LPS)
 Endotoxin or Pyrogen
 Fever causing
 Structure
 Lipid A
 Polysaccharide
 O Antigen of E. coli, Salmonella
 Gram Negative bacteria only

24. LPS (cont’d.)
 Appearance of Colonies
 Mucoid = Smooth (lots of LPS or capsule)
 Dry = Rough (little LPS or capsule)
 O Antigen of Salmonella and E. coli
 2,000 different O Ags of Salmonella
 100’s different O Ags of E. coli
 E. coli O157
 O Ags differ in Sugars, not Lipid A

25. Endospores
 Resistant structure
 Heat, irradiation, cold
 Boiling >1 hr still viable
 Takes time and energy to make
spores
 Location important in classification
 Central, Subterminal, Terminal

26. Chapter 4

27. Comparison