Bacterial Cell
Structure & Function
Dr.Qurat-Ul-Ain
Department Of
Microbiology
KEMU,Lahore
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1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm
1mm = 1000 µm = 1000000nm
1 µm = 1000nm
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Average bacteria 0.5 - 2.0 um in diam.
◦ RBC is 7.5 um in diam.
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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
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Coccus
◦ Chain = Streptoccus
◦ Cluster = Staphylococcus
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Bacillus
◦ Chain = Streptobacillus
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Coccobacillus
Vibrio = curved
Spirillum
Spirochete
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Flagella
Pili
Capsule
Plasma Membrane
Cytoplasm
Cell Wall
Lipopolysaccharid
es
Teichoic Acids
Inclusions
Spores
Cytoplasm:
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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:
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Bacteria’s way of storing nutrients.
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Staining of some granules aids in identification.
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
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Found within cytoplasm or attached to
plasma membrane.
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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
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Peptido-glycan Polymer (amino acids +
sugars)
Unique to bacteria
Sugars; NAG & NAM
◦ N-acetylglucosamine
◦ N-acetymuramic acid
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D form of Amino acids used not L form
◦ Hard to break down D form
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Amino acids cross link NAG & NAM
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 interpeptide bridges.
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
Negative
Gram
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Gram + only
Glycerol, Phosphates, & Ribitol
Attachment for Phages
Participate in MG supply to the cell
Antigenic determinant
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Endotoxin or Pyrogen
◦ Fever causing
◦ Toxin nomenclature
 Endo- part of bacteria
 Exo- excreted into environment
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Structure
◦ Lipid A
◦ Polysaccharide
 O Antigen of E. coli, Salmonella
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G- bacteria only
◦ Alcohol/Acetone removes primary stain durind
gram’s staining.
Chapter 4
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Appearance of Colonies
◦ Mucoid = Smooth (lots of LPS or capsule)
◦ Dry = Rough (little LPS or capsule)
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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
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O Ags differ in Sugars, not Lipid A
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80% Water {20% Salts-Proteins)
◦ Osmotic Shock important
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DNA is circular, Haploid
◦ Advantages of 1N DNA over 2N DNA
◦ More efficient; grows quicker
◦ Mutations allow adaptation to environment quicker
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Plasmids; extra circular DNA
◦ Antibiotic Resistance
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No organelles (Mitochondria, Golgi, etc.)
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.
2.Polysaccharides
to the cell wall.
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firmly attached
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.
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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.
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Motility - movement
Swarming occurs with some bacteria
◦ Spread across Petri Dish
◦ Proteus species most evident
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Arrangement basis for classification
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Monotrichous; 1 flagella
Lophotrichous; tuft at one end
Amphitrichous; both ends
Peritrichous; all around bacteria
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Short protein appendages
◦ smaller than flagella
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Adhere bacteria to surfaces
◦ E. coli has numerous types
 K88, K99, F41, etc.
◦ Antibodies to it will block adherence.
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F-pilus; used in conjugation
◦ Exchange of genetic information
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Resistant structure
◦ Heat, irradiation, cold
◦ Boiling >1 hr still viable
◦ Takes time and energy to destroy spores
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Location important in classification
◦ Central, Subterminal, Terminal
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Bacillus stearothermophilus -spores
◦ Used for quality control of heat sterilization
equipment
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Bacillus anthracis - spores
◦ Used in biological warfare
Spore Formation
This is what happens …………..
Cell
Spore forms
in cell
Cell
disintegrates
Spore is
released
Spore starts
to germinate
Spore continues to
germinate
Now see as, in suitable conditions, the cell begins to divide
(binary fission)………………………….
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Bacteria sometimes occur in groups,
rather than singly.
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_________ divide along a single axis,
seen in pairs or chains.
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_________ 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.