Chair of Medical Biology, Microbiology, Virology, and Immunology
CELL CELL SSTRUCTURE OF BACTERIA.TRUCTURE OF BACTERIA.
Lecturer As. Prof. O. Pokryshko
The Dimension of BacteriaThe Dimension of Bacteria The Dimension of BacteriaThe Dimension of Bacteria
Relative size of a bacterial cell compared to other cells including viruses.
Bacterial surface structuresBacterial surface structures
Cell EnvelopeCell EnvelopeCell EnvelopeCell Envelope
Cytoplasmic membrane Cytoplasmic membrane Cell wallCell wall
Cell wall-less bacteriaCell wall-less bacteria No peptidoglycan layerNo peptidoglycan layer Cell membrane contains sterols for Cell membrane contains sterols for
stabilitystabilityMycoplasma pneumoniae
Cytoplasmic MembraneCytoplasmic MembraneCytoplasmic MembraneCytoplasmic Membrane
Phospholipid bilayerPhospholipid bilayer ““Fluid mosaic” modelFluid mosaic” model
Embedded proteins for active transportEmbedded proteins for active transport
Enzymes for energy generationEnzymes for energy generation Photosynthetic pigmentsPhotosynthetic pigments
Cell membraneCell membrane
PeripheralMembraneProtein
IntegralMembraneProtein
PeripheralMembraneProtein
Phospholipid
Selective permeability to different Selective permeability to different molecules. molecules.
Active transport aided by permease.Active transport aided by permease. Play a role in DNA replication.Play a role in DNA replication. Cell wall biosynthesis.Cell wall biosynthesis. Mesosomes ----- cell division.Mesosomes ----- cell division.
Function of Cytoplasmic MembraneFunction of Cytoplasmic Membrane
Cell wallCell wall Two major groups of bacteria based Two major groups of bacteria based
on structure of cell wallon structure of cell wall Gram positiveGram positive
Thick peptidoglycan layerThick peptidoglycan layer Gram negativeGram negative
Thin peptidoglycan layerThin peptidoglycan layer Outer membrane containing LPSOuter membrane containing LPS
Gram stain is crucial first step toward Gram stain is crucial first step toward identificationidentification
Peptidoglycan (cell wall)Peptidoglycan (cell wall)
Cell WallCell Wall Cell WallCell Wall Gram positive cell wallGram positive cell wall
Thick peptidoglycan (PG) layerThick peptidoglycan (PG) layer Acidic polysaccharidesAcidic polysaccharides Teichoic acid and lipoteichoic acidTeichoic acid and lipoteichoic acid
Gram-negative cell wallGram-negative cell wall Thin peptidoglycan (PG) layerThin peptidoglycan (PG) layer Lipopolysaccharide layerLipopolysaccharide layer PorinsPorins Periplasmic spacePeriplasmic space
Gram-positive cell envelopeGram-positive cell envelope
Gram-negative cell Gram-negative cell envelopeenvelope
Cell Wall StructuresCell Wall Structures Cell Wall StructuresCell Wall Structures
Structures associated with gram-positive and gram-negative cell walls.
Maintenance of the shape (due to rigidity of Maintenance of the shape (due to rigidity of peptidoglycan).peptidoglycan).
Protects the cytoplasmic membrane cell Protects the cytoplasmic membrane cell contentscontents RigidityRigidity Cell wall is osmotically insensitiveCell wall is osmotically insensitive
Hypotonic solution – cell burst.Hypotonic solution – cell burst. Hypertonic solution – cell shrank.Hypertonic solution – cell shrank. Isotonic solution – bacteria is life.Isotonic solution – bacteria is life.
Function of Cell WallFunction of Cell Wall
L FormsL FormsL FormsL Forms
Mutations can cause some bacteria to lose the ability to synthesize the cell wall and are called L forms.
CapsulesCapsules
are important forare important for Adhesion Adhesion (Associated with virulence in bacteria) Avoidance of immune responseAvoidance of immune response
(Protects bacteria from phagocytic cells)(Protects bacteria from phagocytic cells) Protection from dehydrationProtection from dehydration
CapsuleCapsule
Klebsiella pneumoniaeBacillus anthracis
Streptococcus pneumoniae
External structuresExternal structures Pili (Pili (Fimbriae) play roles inplay roles in
AdhesionAdhesion Exchange of genetic materialExchange of genetic material Avoidance of immune responseAvoidance of immune response
FlagellaFlagella are important for are important for Motility (dispersal)Motility (dispersal) Antigenic determinant (Antigenic determinant (“H” antigens)
Number and location species specificNumber and location species specific
Pili and flagellaPili and flagella
Salmonella
Fimbriae are smaller than flagella and are important for attachment.
Pili Pili Pili Pili
Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another (“mating”).
Flagellar StructureFlagellar StructureFlagellar StructureFlagellar Structure
Three components of a flagellum: filament, hook and basal body
It composed of protein subunits calledIt composed of protein subunits called flagellinflagellin..
Flagellar ArrangementFlagellar ArrangementFlagellar ArrangementFlagellar Arrangement
(a) Monotrichous (b) Lophotrichous(c) Amphitrichous (d) Peritrichous
Bacterial MotilityBacterial MotilityBacterial MotilityBacterial Motility
The rotation of the flagella enables bacteria to be motile.
CytoplasmCytoplasm Genome Genome Inclusion bodiesInclusion bodies EndosporeEndospore
Internal StructuresInternal Structures
CytoplasmCytoplasmCytoplasmCytoplasm
Gelatinous solution containing Gelatinous solution containing
water, nutrients, proteins, and water, nutrients, proteins, and
genetic materialgenetic material
Site for cell metabolism Site for cell metabolism
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Chemical Analysis of Microbial Chemical Analysis of Microbial CytoplasmCytoplasm
70% water70% water ProteinsProteins 96% of cell is composed of 6 elements:96% of cell is composed of 6 elements:
carboncarbon hydrogenhydrogen oxygenoxygen phosphorousphosphorous sulfursulfur nitrogennitrogen
Bacterial GenomeBacterial Genome Bacterial GenomeBacterial Genome
Most bacteria contain a single circular double strand of DNA called a nucleoid.
Prokaryotic RibosomeProkaryotic RibosomeProkaryotic RibosomeProkaryotic Ribosome
A ribosome is a combination of RNA and protein, and is the site for protein synthesis
Composed of large (50S) and small (30S) subunits
S = Svedverg unit, measures molecular size
Inclusion BodiesInclusion BodiesInclusion BodiesInclusion Bodies
Inclusion bodies enable a cell to store nutrients and to survive in nutrient depleted environments
Some bacteria, notably those of the Some bacteria, notably those of the
genera Bacillus and Clostridium, develop genera Bacillus and Clostridium, develop
a highly resistant resting phase or a highly resistant resting phase or
endospore that does not grow or endospore that does not grow or
reproduce and exhibit absolute dormancy reproduce and exhibit absolute dormancy
(not detectable metabolism). (not detectable metabolism).
Bacterial SporesBacterial Spores
EndosporesEndospores
Bacillus anthracis
Vegatitive formVegatitive form The bacteria actively growing, non spore The bacteria actively growing, non spore
stage of a bacterium.stage of a bacterium. Sporulation:Sporulation:
Formed on exposure to unfavorable Formed on exposure to unfavorable condition,E.g., condition,E.g.,
Nutrient depletion Nutrient depletion ChangesChanges
Moisture,Moisture, Temperature, Temperature, pH orpH or Oxygen tensionOxygen tension
Spore requires 10-15 hours to form.Spore requires 10-15 hours to form.
Endospore formationEndospore formation
GerminationGermination Mature endoscope are metabolically inertMature endoscope are metabolically inert Changes in the environmentChanges in the environment
Retuning to vegetative state within 15 Retuning to vegetative state within 15 minutes.minutes.
In the process of germination the spores In the process of germination the spores absorb water and swell, the protective absorb water and swell, the protective coat disintegrates and a single vegatitive coat disintegrates and a single vegatitive cell emerges.cell emerges.