1. Bacterial Cell
Structure & Function
Dr.Qurat-Ul-Ain
Department Of Microbiology
KEMU,Lahore

2. Two Basic Types of Cells
Prokaryotic Cells (Prokaryotes)
Eukaryotic Cells (Eukaryotes)
______________
_____________________

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

4. Size of Bacteria Average bacteria 0.5 - 2.0 um in diam.
RBC is 7.5 um in diam.
Surface Area ~12 um^2
Volume is ~4 um
Surface Area to Volume is 3:1
Typical Eukaryote Cell SA/Vol is 0.3:1
Food enters through SA, quickly reaches all parts of bacteria
Eukaroytes need structures & organelles

5. Shapes of Bacteria Coccus Bacillus Coccobacillus Vibrio = curved
Chain = Streptoccus
Cluster = Staphylococcus
Bacillus
Chain = Streptobacillus
Coccobacillus
Vibrio = curved
Spirillum
Spirochete

6. Bacterial Structures Flagella Pili Capsule Plasma Membrane Cytoplasm
Cell Wall
Lipopolysaccharid es
Teichoic Acids
Inclusions
Spores

7. Prokaryotes Cytoplasm: Also known as proto-plasm.
Gel-like matrix of water, enzymes, nutrients, wastes, (organic n inorganic solutes) and gases and contains cell structures like numerous ribosomes and polysomes.
No ER n memb.bound organelles.
Shows signs of internal mobility like cytoplasmic streaming , amoeboid movement and formation and disappearance of vacoules.
Location of growth, metabolism, and replication.
Granules or inclusions:
Bacteria’s way of storing nutrients.
Staining of some granules aids in identification.
Cytoplasm
Granules

8. Prokaryotes Ribosomes: Small electron dense particles
Involved in prt.synthesis
70 S(30 S + 50S)
Different from host cell ribosomes in SR.
Streptomycin interferes with bacterial metabolism sparing the host cell ribosomes.
3 types of RNAs:
Ribosomal, transfer , mRNA
Found within cytoplasm or attached to
plasma membrane.
Ribosomes

9. 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
Hydrophilic
hydrophobic
Some materials can move across the membrane, others cannot.

10. Cell Wall Peptido-glycan Polymer (amino acids + sugars)
Unique to bacteria
Sugars; NAG & NAM
N-acetylglucosamine
N-acetymuramic acid
D form of Amino acids used not L form
Hard to break down D form
Amino acids cross link NAG & NAM

12. Prokaryotes – Cell Wall
Peptidoglycan is a huge polymer of interlocking chains of identical peptidoglycan monomers.
Provides rigid support while freely permeable to solutes.
Backbone of peptidoglycan molecule composed of two derivatives of glucose:
- N-acetylglucosamine (NAG)
- N-acetlymuramic acid (NAM)
NAG / NAM strands are
connected by inter-
peptide bridges.

13. Prokaryotes - Cell Wall
From the peptidoglycan inwards all bacteria are very similar. Going further out, the bacterial world divides into two major classes (plus a couple of odd types). These are:
Gram Positive Gram Negative
positive
negative

14. Prokaryotes - Cell Wall Gram-Positive & Gram-Negative
Peptidoglycan makes up as much as 90% of the thick, compact cell wall.
Gram-negative
More chemically complex and thinner.
Peptidoglycan only 5 – 20% of the cell wall.
Peptidoglycan not outermost layer, between the plasma membrane and the outer membrane.
Outer membrane is similar to the plasma membrane, but is less permeable and composed of lipopolysaccharides (LPS).
LPS is a harmful substance classified as an endotoxin,
The space between the cell wall and the plasma membrane is called the periplasm.

15. Q: Why are these differences in cell wall structure so important?
Gram-negative bacteria: fewer interpeptide bridges but have an outer membrane made of lipopolysaccharides LPS.
Penicillins and cephalosporins interfere with linking of interpeptides, but can’t easily get to in gram- bacteria.
Cell walls without enough of these intact cross-links are structurally weak, and disintegrate when cells divide. This is how penicillins and cephalosporins work.
Since the eukaryotic cells of humans do not have cell walls, our cells are not damaged by these drugs.
Microorganisms that do not contain peptidoglycan are not susceptible to these drugs.

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

17. 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.

18. Chapter 4

19. 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

20. Cytoplasm 80% Water {20% Salts-Proteins) DNA is circular, Haploid
Osmotic Shock important
DNA is circular, Haploid
Advantages of 1N DNA over 2N DNA
More efficient; grows quicker
Mutations allow adaptation to environment quicker
Plasmids; extra circular DNA
Antibiotic Resistance
No organelles (Mitochondria, Golgi, etc.)

21. Prokaryotes - Glycocalyx
Some bacteria have an additional layer outside of the cell wall called the glycocalyx.
This additional layer can come in one of two forms:
1- Glycoproteins loosely associated with the cell wall.
- Slime layer causes bacteria to adhere to solid surfaces and helps prevent the cell from drying out.
- Streptococcus
The slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities).
Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque.
Slime layer

22. 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.
Capsule

23. Prokaryotes – Surface Appendages
Some prokaryotes have distinct appendages that allow them to move about or adhere to solid surfaces.
Consist of delicate strands of proteins.
Flagella: Long, thin extensions that allow some bacteria to move about freely in aqueous environments.
Endoflagella: Wind around bacteria, causing movement in waves.
Flagella
Axial filaments
Fimbria
Pili

24. 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

25. Pili Short protein appendages Adhere bacteria to surfaces
smaller than flagella
Adhere bacteria to surfaces
E. coli has numerous types
K88, K99, F41, etc.
Antibodies to it will block adherence.
F-pilus; used in conjugation
Exchange of genetic information

26. Endospores Resistant structure Location important in classification
Heat, irradiation, cold
Boiling >1 hr still viable
Takes time and energy to destroy spores
Location important in classification
Central, Subterminal, Terminal
Bacillus stearothermophilus -spores
Used for quality control of heat sterilization equipment
Bacillus anthracis - spores
Used in biological warfare

27. Spore Formation
This is what happens …………..
Cell

28. Spore forms in cell

29. Cell disintegrates

30. Spore is released

31. Spore starts to germinate

32. Spore continues to germinate

33. Now see as, in suitable conditions, the cell begins to divide (binary fission)………………………….

35. Prokaryotes – Arrangements of Cells
Bacteria sometimes occur in groups, rather than singly.
_________ divide along a single axis, seen in pairs or chains.
_________ divide on one or more planes, producing cells in:
- pairs (diplococci)
- chains (streptococci)
- packets (sarcinae)
- clusters (staphylococci).
Size, shape and arrangement of cells often first clues in identification of a bacterium.
Many “look-alikes”, so shape and arrangement not enough for id of genus and species.
Bacillus
Coccus