cell morphology
TRANSCRIPT
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Functional anatomy of Bacteria
MANISH BANSAL
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Comparing prokaryotic and eukaryotic
cells Prokaryotes
DNA is notenclosed in a membrane
Lack membrane-boundorganelles
Cell walls contain peptidoglycan
Reproduce by binary fission
Eukaryotes DNA issurrounded by nuclearmembrane
Have many membrane-boundorganelles
Cell walls, when present,areusuallysimple
Usuallydivide by mitosis
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Proks and euks are similar in chemical composition and reaction
Proks lack membrane
boundorganelles
OnlyProks have
peptidoglycan
Euks have membrane
boundorganelles
Euks have paired
chromosomes Euks have histones
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Bacterial cell
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Bacterial cell
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The prokaryote
Unicellular
Multiply by binary fission
Classified by
Morphology Chemical composition
Nutritional requirements
Biochemical activates
Sourcesofenergy
Othertests
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Size
0.2to2um in diameter
2-8um in length
In biological systemstherearealways
exceptionsthesearegeneral sizes.
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Shape
Coccus
Diplococci
Streptococci
Staphylococci
Bacillus
Spiral
Otherpleomorphic
shapes
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Cocci
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Bacilli
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Vibrio, spirillum, spirochete.
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Structures external to cell wall
Glycocalyx
Capsule
Slime layer
Flagella
Axial filaments
Fimbriae
Pili
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Parts not seen
Glycocalyx
Capsule
Slime layer
Extracellularpolysaccharide
Function
Toxicity
Protect from
phagocytosis
Allow adherence
Reduce water loss
Collect nutrients
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Flagella
Used in movement
Can presenttaxis
Negative
Positive
FlagellarH protein actsasan antigen
Flagellin
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Flagella Arrangement
Figure 4.7
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Flagella: Structure
Long filamentous appendages with filament, hook and basal body
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Fimbriae/pili
Shorterand less
complexthan flagella
Helpsadhereto
surfaces Used forsexand
communication
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Cell Walls
Whystudy bacterial cell walls?
Theyareessential structures in bacteria.
Theyare madeof chemical components found
nowhereelse in nature.
They may causesymptomsofdisease in animals.
Theyarethesiteofaction ofsomeofourmost
importantantibiotics.
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Cell wall
Majordifference between eukaryotic and prokorgs.
Surrounds plasma membrane provides protection
Peptidoglycan
Polymerof
NAG
NAM Shortaminoacid chain
Preventsosmotic damage
Damageto cw isalmostalways lethal except
Production inhibited byantibiotics
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Profile of the bacterial cell envelope
Gram-positive cell wall isthick homogeneousmonolayer
Gram-negative cell wall isthin heterogeneous
multilayer
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Cell wall
Gram-positive cell wall
Madeof peptidoglycan in multiple layers
(complex)
Containstechoic acids
Gram-negative cell wall
Madeofone layerof peptidoglycan (simple)
Notechoic acid is present Outermembrane with lipopolysaccharides
Lipid portion of lipopolysaccharide isendotoxin
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Structure of cell wall in gram positive bacteria
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Gram Positives have thick cell wall
andT
eichoic acids
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Gram negative
Lipoprotein phospholipidoutermembranesurroundingathin peptidoglycan
Makesgram negresistantto Phagocytosis Antibiotics
Chemical reactions
Enzymes (lysozyme)
Has lipid A endotoxin
O polysaccarideantigen.
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Gram-Negative Outer Membrane
Figure 4.13c
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Chemical nature of bacterial cell walls
Bacterial cell wallsalways
contain murein, which isa
typeof peptidoglycan
Chemical natureof murein
accounts forthe function of
the cell wall
Murein isonly found in the
cell wallsof bacteria
E. colipeptidoglycan
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Chemical nature of bacterial cell walls
Peptidoglycan is madeup of
2aminosugarsN-acetyl-glucosamine = GN- acetylmuramic acid = M
4 aminoacidsL-alanine = L-alaD-glutamic acid = D-glu
diaminopimelic acid = DAPD-alanine = D-ala
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Chemical nature of bacterial cell walls
Gram-negative murein showingthesitesofaction oftheantibioticpenicillin andtheenzyme lysozyme
Penicillin prevents
formation ofthis
Interpeptide bond
Lysozyme breaksthis
glycoside bond between
M andG
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Chemical nature of bacterial cell walls
Gram-positive murein hasathickerglycan a backboneandthereareinterpeptide bridgesthatjoin aminoacidside chainstogether.
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Chemical nature of bacterial cell walls
Gram-positive murein showingthesitesofaction oftheantibiotic penicillinandtheenzyme lysozyme
Penicillin blocksthe
Insertion ofthe inter-
peptide bridge
Lysozyme breaksthe
glycoside bond between
M andG
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Other characteristics of bacterial cell walls
Gram-positive cell walls contain teichoic acids
Teichoic acidsarethoughttostabilizethe
Gram positive cell wall and may beused in adherence.
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Other characteristics of bacterial cell walls
OutermembraneofGram-negatives hastwo important properties
1. It protectsthe cells from permeability by manysubstancesincluding penicillin and lysozyme.
2. It isthe location of lipopolysaccharide (endotoxin) which istoxicforanimals.
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Table: Correlation of the Gram stain withproperties of bacterial cell walls
Property Gram-positive Gram-negative
Thicknessof wall thick (20-80 nm) thin (10 nm)
Numberof layers 1 2-3
Peptidoglycan (murein)
content
>50% 10-20%
Teichoic acids in wall present absent
Protein/lipoprotein
content
0-3% >50%
Lipopolysaccharide
content
0 13
Sensitivityto penicillin sensitive resistant
Sensitivityto lysozyme sensitive resistant
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Primary function of the bacterial cell wall
To prevent
ruptureor
osmotic lysisof
the cellprotoplast
Lysisofa pairofdividingE. colicells
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Cell walls can be removed for genetic
transfer
Protoplast
Gram-positive cell without cell wall
Spheroplast
Gram-negative cell without cell wall
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Nontypical cell walls
Mycoplasma (acid fast)do not have ppt
containing cell wall.
Archaea contain anotherchemical called
pseudomurein
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Structures internal to cell wall
Plasma membrane
Selectively permeable fluid mosaic model
Movement of materialsacross plasma membrane
Passive processes
Diffusion
Facilitateddiffusion
Osmosis
Active processes Activetransport
Group translocation
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Plasma membrane
Definesthe livingand nonliving partsofthe
cell
Everythingon the inside is living
Everythingon theoutside is not living
Isselectively permeable
Workspace forenzymesof metabolic
reactions
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Cell (cytoplasmic) membrane
Completelyenclosesthe bacterial cellprotoplast
Composedof 60%
protein and 40%phospholipid
Arrangedasa bilayer
Section ofa cytoplasmic membrane
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Plasma Membrane
Phospholipid bilayer Peripheral proteins
Integral proteins
Transmembrane proteins
Figure 4.14b
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Membrane isasviscousasoliveoil.
Proteins moveto function
Phospholipidsrotateand move laterally
Fluid Mosaic Model
Figure 4.14b
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M b d bl
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Membrane structure and assembly
The membranebilayer isformed byphospholipidm
olecules madeup ofglyceroland fattyacids
M b d bl
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Membrane structure and assembly
Phospholipids
arrange
themselves
spontaneously in
water: lipid tailsinward;glycerol
headsoutward
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Transport systems in bacteria
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Structures internal to cell wall
Cytoplasm
Nucleararea
Chromosomes
Plamid(s)
Ribosomes
Inclusionsandgranules
Metachromatic phosphate
Sulfur
Magnetosomes
Endospores
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Membrane activity
Diffusion
Osmosis
Passivediffusion
Facilitateddiffusion
Activetransport
Know therelationships
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Activetransportofsubstancesrequiresa
transporterprotein and ATP.
Group translocation ofsubstancesrequiresa
transporterprotein andPEP.
Movement Across Membranes
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PM Workspace
Nutrient breakdown
Energy production
Photosynthesis
Afforded by mesosomes which areregular infoldingsofthe plasma membrane
Weaknesses: destroyed byactionsofalcohols,
quaternaryammonium (detergents)and
polymyxinsantibiotics.Damagetothe membrane
causes leakageof cell contents.
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Functions of the cytoplasmic membrane
Osmotic orpermeability barrier:the membrane isimpermeableto moleculesthatare chargedorgreaterthan molecularweightof100
Location oftransportsystemsto importall theneeded moleculesthatare chargedorgreaterthanmolecularweight100
Energygeneration: location oftheelectron
transportsystem (ETS)andthe ATPsynthsizingenzyme ATPase
Specialized functions involving cell wall synthesis,cell division andDNA replication.
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Cytoplasmic Constituents of Bacterial
C
ells Cytoplasm
Genetic material: chromosomeandPlasmids
(DNA)
Ribosomes
Inclusions
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Cytoplasm's
The liquid componentofthe cell within the
PM
Mostly water,dissolved ions,DNA ribosomes
and inclusions
Conceptof homeostasis
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The Bacterial ChromosomeorNucleoid
Bacterial DNA released from
a gently lysed E. coli cell
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Ribosomes
Figure 4.19
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Ribosomesare madeoftwosubunits,a largesubunitanda
small subunit. Each subunit is madeup of RNA andvarious
proteins.
Ribosome StructureandComposition
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Ribosomes function in protein synthesis. Aminoacidsare
assembled into proteinsaccordingtothegenetic codeon
thesurfacesofribosomesduringthe processoftranslation.
RibosomeFunction
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Inclusions
Typicallyreservedepositsofexcess
materials like inorganic phosphate
Polysaccharidegranules
Lipids
Sulfur
Gas
iron
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Inclusion Composition
Glycogen poly-glucose Reserve carbon andenergy
source
Poly-betahydroxybutyric
acid (PHB)
lipid Reserve carbon andenergy
source
Poly-phosphates polymersofPO4 Reserve phosphate,
possibly high-energyPO4
Sulfurglobules elemental S Reserveenergyandor
electrons
Magnetosomes magnetite (iron oxide) Provideorientation in
magnetic field
Gasvesicles protein shells inflated with
gases
Provide buoyancy in aquatic
environments
Parasporal crystals protein Produced byendospore-
forming Bacilli - toxic to
insects
Function
Some inclusions in Bacterial Cells
S i l i i B t i l C ll
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Some inclusions in Bacterial Cells
Bacterial Inclusions.A.PHB granules; b.a parasporal BT crystal in thesporangium of
Bacillus thuringiensis; c. carboxysomes inAnabaena viriabilis,showingtheirpolyhedral
shape;d.sulfurglobules in the cytoplasm ofBeggiatoa.
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Endospores
Restingand waiting
stage
Resistanttodryingand
otherharsh conditions
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Formation of spores
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Endosporesare producedas intracellularstructures within the cytoplasm
of certain bacteria, most notablyBacillus andClostridium species.
Endospore forming bacteria lefttoright:Clostridium botulinum, Bacillus brevis, Bacillus thuringiensis
Under favorable nutritional and environmental conditions an
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Under favorable nutritional andenvironmental conditions,an
endosporegerminates intoavegetative cell.
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Medically-important Endospore-
forming Bacteria Bacillus anthracis causesanthrax Bacillus cereus causes food poisoning
Clostridium tetanicausestetanus
Clostridium botulinum causes botulism Clostridium perfringens causes food poisoningand
gasgangrene
Clostridium difficile causesantibiotic-induced
diarrheaand pseudomembranous colitis
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Properties ofEndospores
Endospore formation is NOT a mechanism of
reproduction. Rather it isa mechanism forsurvival in
deleteriousenvironments. Duringthe processofspore
formation,onevegetative cell develops intoone
endospore.
Resting (dormant) cells- cryptobiotic i.e.,show nosigns
of life..primarilydueto lackof water in thespore
Several uniquesurface layers not found in vegetativecells:exosporium,spore coat, cortex,and core wall
Highlyresistantto heat (boiling),acids, bases,dyes ( dont
stain) irradiation,disinfectants,antibiotics,etc.
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Properties ofEndospores
Sporesand parasporal crystals produced bysome
bacteriaaretoxic to insects
Parasporal crystalEndospore
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