Cell Morphology

8/6/2019 Cell Morphology

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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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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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Gram-negative murein showingthesitesofaction oftheantibioticpenicillin andtheenzyme lysozyme

Penicillin prevents

formation ofthis

Interpeptide bond

Lysozyme breaksthis

glycoside bond between

M andG


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Gram-positive murein hasathickerglycan a backboneandthereareinterpeptide bridgesthatjoin aminoacidside chainstogether.


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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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Cell Morphology