BIOL 3340 BIOL 3340 Chapter 3Chapter 3

Chapter 3 Chapter 3

Microbial Cell Structure

Types of CellsTypes of CellsTwo major classes: eukaryotes & prokaryotes.

Differences: the materials making up the nucleus of eukaryotic cells are separated from the rest of the cell by the nuclear membrane, whereas in prokaryotic cells these materials are not separated.

• All animals and plant cells are eukaryotic including fungi. Bacteria, cyanobacteria and the mycoplasmas are prokaryotic.

Size, Shape, and Arrangement of Bacterial cells

Cocci (s., coccus) – spheresdiplococci (s., diplococcus) – pairsstreptococci – chainsstaphylococci – grape-like clusterstetrads – 4 cocci in a squaresarcinae – cubic configuration of 8 cocci

……Size, Shape, and Arrangement

Bacilli (s., bacillus): – rodscoccobacilli – very short rodsvibrios – resemble rods, comma

shapedspirilla (s., spirillum) – rigid helicesspirochetes – flexible helicesmycelium – network of long,

multinucleate filaments Check on line lab Manual for Bacterial shapes)

……Size, Shape, and Arrangement

Sizes: Typically ~ 0.1 - 20 m (with some

exceptions)Typical coccus: ~ 1 m (e.g. Staphylococcus

)Typical short rod: ~ 1 x 5 m (e.g. E. coli)Barely within the best resolution of a

good compound light microscope

Bacterial Shapes

Cell Structureof Procaryotes

Prokaryotic cellsThe constituents of a typical bacterium are as follows:

Bacterial Cell Wall and Capsule – bacteria are surrounded by a cell wall, which not only contains polysaccharide but also contains protein and lipid.

In some bacteria, the cell wall is surrounded by the capsule.

The cell wall and capsule provide shape and form to the bacterium and also acts as a physical barrier between the bacterium and its environment.

Nucleoids – in bacteria the nuclear material is concentrated in a region called the nucleoid within the cytoplasm.

A typical Bacterial CellA typical Bacterial Cell

….Cell Structure

There is no membrane-bound nucleus in prokaryotes.

Instead the DNA is located within a specialized region of the cytoplasm of the cell called the nucleoid region.

There is no nuclear membrane surrounding the nucleoid.

Bacterial flagella – many bacteria possess one or more flagella for locomotion.

Gram-negative Cell Walls and Acid Fast Fast cell wall in

Chapter 3

Procaryotic Cell Membranes

Cell Membranes:membranes are an absolute

requirement for all living organisms.

plasma membrane encompasses the cytoplasm

some procaryotes also have internal membrane systems

Functions of the Plasma Membrane

separation of cell from its environmentselectively permeable barrier

some molecules are allowed to pass into or out of the cell

transport systems aid in movement of molecules

detection of and response to chemicals in surroundings with the aid of special receptor molecules in the membrane

Fluid Mosaic Model of Membrane Structure

…..Plasma membrane

…..Plasma membrane

…Phospholipid layer

polar endsinteract with waterhydrophillic

nonpolar endsinsoluble in waterhydrophobic

Membrane Proteins

Peripheral proteins:loosely associated with the membrane

and easily removed

Integral proteinsembedded within the membrane and

not easily removed

Procaryotic Cytoplasm

Cytoplamic Matrix:Cytoplasm contains the nucleoid,

ribosomes and inclusion bodies lacks organelles bound by unit

membranescomposed largely of wateris a major part of the protoplasm (the

plasma membrane and everything within)

..Cytoplasmic Matrix

Viscous aqueous suspension of proteins, nucleic acid, dissolved organic compounds, mineral salts

Network of protein fibers similar to the eukaryotic cytoskeleton.

Cytoplasmic Inclusion Bodies: granules of organic or inorganic material

that are stockpiled by the cell for future use.

some are enclosed by a single-layered membrane

….Cytoplasmic inclusions

Cytoplasmic inclusions:Glycogen GranulesPoly--hydroxyutyrate granulesLipid dropletsGas vacuolesMetachromatic granules

(Phosphate crystals or volutin granules)Sulfur Granules

Ribosomes

Ribosomes:complex structures consisting of

protein and RNAsites of protein synthesissmaller than eucaryotic ribosomes

procaryotic ribosomes 70Seucaryotic ribosomes 80S

The Nucleoid

Nucleoid:irregularly shaped regionlocation of chromosome

usually 1/cellnot membrane-bound

The Procaryotic Chromosome

The Chromosomes:usually a closed circular, double-

stranded DNA moleculelooped and coiled extensively

Plasmids

Plasmids:usually small, closed circular DNA

moleculesexist and replicate independently of

chromosomehave relatively few genes present

Procaryotic Cell Walls

Prokaryotic Cell Wall:rigid structure that lies just outside

the plasma membrane (detail to continue)

Functions of Cell Wall

provides characteristic shape to cellprotects the cell from osmotic lysismay also contribute to pathogenicityvery few procaryotes lack cell walls

Cell Walls of Bacteria

Gram Staining developed by Gram in 1888:

bacteria are divided into two major groups based on the response to gram-stain proceduregram-positive bacteria stain purplegram-negative bacteria stain pink

staining reaction due to cell wall structure

Gram Positive and Gram negative

Gram-Positive Cell WallsGram-Positive Cell Walls

Gram positive bacteria composed Gram positive bacteria composed primarily of primarily of peptidoglycanpeptidoglycan

Peptidoglycan are polymers which Peptidoglycan are polymers which contains contains NN-acetylglucosamine and -acetylglucosamine and NN--acetylmuramic acid and several acetylmuramic acid and several different amino acidsdifferent amino acids

• Walls contain teichoic acid (Walls contain teichoic acid ( polymers polymers of glycerol or ribitol joined by phosphate of glycerol or ribitol joined by phosphate groups)groups)

..Gram-Positive Cell Walls..Gram-Positive Cell Walls

The The periplasmic periplasmic space lies between space lies between plasma membrane and cell wall and plasma membrane and cell wall and is smaller than that of gram-negative is smaller than that of gram-negative bacteriabacteria

periplasm periplasm has relatively few proteins has relatively few proteins enzymes secreted by gram-positive enzymes secreted by gram-positive

bacteria are called exoenzymesbacteria are called exoenzymes

Gram-Negative Cell WallsGram-Negative Cell Walls

consist of a thin layer of consist of a thin layer of peptidoglycan surrounded by an peptidoglycan surrounded by an outer membraneouter membrane

outer membrane composed of lipids, outer membrane composed of lipids, lipoproteins, and lipoproteins, and lipopolysaccharide lipopolysaccharide (LPS)(LPS)

no teichoic acidsno teichoic acids

……..Gram Negative..Gram Negative

more complex than gram-positive more complex than gram-positive wallswalls

periplasmic space differs from that in periplasmic space differs from that in gram-positive cellsgram-positive cellsmay constitute 20-40% of cell volumemay constitute 20-40% of cell volumemany enzymes present in periplasmmany enzymes present in periplasm

Gram Positive and Negative Gram Positive and Negative cell Wallcell Wall

AssignmentsAssignments

Features of a prokaryotic cellFeatures of a prokaryotic cellList the differences between a gram List the differences between a gram

positive and gram negative cell wall.positive and gram negative cell wall.

Variations on Cell Wall Variations on Cell Wall ArchitectureArchitecture

Acid-fast Cell Walls::Many genera in the “High GC gram-Many genera in the “High GC gram-

positive” bacterial group contain positive” bacterial group contain mycolic acids, embedded in the , embedded in the peptidoglycan .peptidoglycan .

Mycolic acids are a class of waxy, Mycolic acids are a class of waxy, extremely hydrophobic lipids.extremely hydrophobic lipids.

Certain genera contain very large amounts Certain genera contain very large amounts of this lipid, and are difficult to gram stain.of this lipid, and are difficult to gram stain.

These genera may be identified by the These genera may be identified by the “acid-fast” staining technique..

Includes Includes Mycobacterium and and Nocardia..

..Variations on Cell Wall ..Variations on Cell Wall ArchitectureArchitecture

Mycoplasmas::Bacteria that are naturally have no cell wallsBacteria that are naturally have no cell wallsIncludes Includes MycoplasmaMycoplasma and and UreaplasmaUreaplasma

Archaea :Archaea :Have archaea cell walls with no peptidoglycanHave archaea cell walls with no peptidoglycanMany have cell walls containing Many have cell walls containing

pseudomurein, a polysaccharide similar to pseudomurein, a polysaccharide similar to peptidoglycan but containing N-peptidoglycan but containing N-acetylglucosamine and N-acetylglucosamine and N-acetyltalosaminuronic acid .acetyltalosaminuronic acid .

Capsules, Slime Layers, and Capsules, Slime Layers, and S-LayersS-Layers

Layers of material lying outside the cell Layers of material lying outside the cell wallwallcapsulescapsules

usually composed of polysaccharidesusually composed of polysaccharideswell organized and not easily removed from well organized and not easily removed from

cellcellslime layersslime layers

similar to capsules except diffuse, similar to capsules except diffuse, unorganized and easily removed. unorganized and easily removed.

a capsule or slime layer composed of a capsule or slime layer composed of polysaccharides can also be referred to as a polysaccharides can also be referred to as a glycocalyxglycocalyx

GlycocalyxGlycocalyx

S-layers:S-layers:

S-layers:S-layers:regularly structured layers of protein or regularly structured layers of protein or

glycoprotein.glycoprotein.in bacteria the S-layer is external to the in bacteria the S-layer is external to the

cell wall.cell wall.Regular “floor tile” pattern.Regular “floor tile” pattern.Function not clear -- Stability? Function not clear -- Stability?

Functions of Capsules, Slime Functions of Capsules, Slime Layers, and S-layersLayers, and S-layers

protection from host defenses (e.g., protection from host defenses (e.g., phagocytosis)phagocytosis)

protection from harsh environmental protection from harsh environmental conditions (e.g., desiccation) , conditions (e.g., desiccation) , chemicals or osmotic stresschemicals or osmotic stress

attachment to surfacesattachment to surfacesfacilitate motilityfacilitate motilitynutrient Storage nutrient Storage

Pili and FimbriaePili and Fimbriae

Fimbriae (s., fimbria)Fimbriae (s., fimbria)short, thin, hairlike, proteinaceous short, thin, hairlike, proteinaceous

appendages up to 1,000/cellappendages up to 1,000/cellmediate attachment to surfacesmediate attachment to surfaces

sex pili (s., pilus):sex pili (s., pilus):similar to fimbriae except longer, similar to fimbriae except longer,

thicker, and less numerous (1-10/cell)thicker, and less numerous (1-10/cell)required for matingrequired for mating

FimbriaeFimbriae

……FimbriaeFimbriae

Function s:Function s:MobilityMobilityAlmost all motile bacteria are motile by Almost all motile bacteria are motile by

means of flagellameans of flagellaMotile vs. non motile bacteria.Motile vs. non motile bacteria.Different species have different flagella Different species have different flagella

arrangementsarrangements

Structure:Structure:Filament composed of the protein flagellinFilament composed of the protein flagellinHook & Rotor Assembly & Permits rotational Hook & Rotor Assembly & Permits rotational

"spinning" movement"spinning" movement

……FimbriaeFimbriae

ChemotaxisChemotaxis

movement towards a chemical movement towards a chemical attractant or away from a chemical attractant or away from a chemical repellentrepellent

concentrations of chemical concentrations of chemical attractants and chemical repellents attractants and chemical repellents detected by detected by chemoreceptorschemoreceptors on on surfaces of cellssurfaces of cells

Bacterial EndosporesBacterial Endospores

Bacterial SporesBacterial Spores are formed by some bacteria as dormant are formed by some bacteria as dormant

structures.structures. resistant resistant to numerous environmental to numerous environmental

conditions e.g heat, radiation,chemicals, conditions e.g heat, radiation,chemicals, nutrient depletion, nutrient depletion,

desiccation, and waste buildup .desiccation, and waste buildup . Bacterial spores are NOT a reproductive Bacterial spores are NOT a reproductive

structure, like plant or fungal spores.structure, like plant or fungal spores. Produced by very few genera of bacteria Produced by very few genera of bacteria Major examples Major examples BacillusBacillus & & ClostridiumClostridium

……endosporesendospores

SporogenesisSporogenesis

SporogenesisSporogenesis

Sporogenesis:Sporogenesis: Also called Also called endosporeendospore formation or formation or sporulationsporulation normally commences when growth ceases normally commences when growth ceases

because of lack of nutrientsbecause of lack of nutrients A copy of the bacterial chromosome is A copy of the bacterial chromosome is

surrounded by a thick, durable spore coat .surrounded by a thick, durable spore coat . When the vegetative cell dies and ruptures, the When the vegetative cell dies and ruptures, the

free spore is released.free spore is released. When spore encounters favorable growth When spore encounters favorable growth

conditions, spore coat ruptures and a new conditions, spore coat ruptures and a new vegetative cell is formed.vegetative cell is formed.

..Sporogenesis..SporogenesisComplex multistage processComplex multistage process

Spore GerminationSpore Germination

BibliographyBibliography

http://en.wikipedia.org/wiki/Scientific_methodhttp://en.wikipedia.org/wiki/Scientific_method https://files.kennesaw.edu/faculty/jhendrix/https://files.kennesaw.edu/faculty/jhendrix/

bio3340/home.htmlbio3340/home.html Lecture PowerPoints Prescott’s Principles of Lecture PowerPoints Prescott’s Principles of

Microbiology-Mc Graw Hill Co.Microbiology-Mc Graw Hill Co. http://www.bio.mtu.edu/campbell/http://www.bio.mtu.edu/campbell/

prokaryo.htmhttp://molecular-prokaryo.htmhttp://molecular-biology.suite101.com/article.cfm/cell_structurebiology.suite101.com/article.cfm/cell_structure

http://water.me.vccs.edu/courses/ENV108/http://water.me.vccs.edu/courses/ENV108/lesson5_2.htmlesson5_2.htm