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.