Disperse System

ColloidsThose dispersions in which size of

dispersed particle is within the range 10-9 (1nm) to about 10 -6m (1Um) are

termed as colloids.

BACTERIA

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Bateria

• Bacteria are smallest & simplest microorganism having definite shape with different nucleus and are capable of performing vital functions of life.(Prokaryotes).

Morphological Features:

• Size:• Range from 0.2um to 5 um In many species of bacteria, bacillus is as

long as 20um & as short as 0.5um.• they vary from 0.5-1.0um in diameter.

Bacterial Cells:

• Shapes & Arrangements– Round Bacteria

Coccus Staphylococcus

Diplococcus Tetrad

Streptococcus Sarcina

– Rod-shaped BacteriaBacillus Streptobacillus

Diplobacillus

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• Shapes & Arrangement:

• Three typical shapes of bacteria are1)Rounded2) Rods3) Spiral shape (spirilla),4) Filamentous shape (Streptomyces)

Shapes of Bacteria• Coccus

– Chain = Streptoccus– Cluster = Staphylococcus

• Bacillus– Chain = Streptobacillus

Coccobacillus• Vibrio = curved• Spirillum• Spirochete• Square

Chapter 4

Shape and Arrangement:

• Cocci:• Diplococci: Occur in pairs,e.g,Neisseria gonorrhea• Streptococci: Occur in Chains, e.g; Streptococcus Pyogenes• Tetrods: Group of four cocci, e.g; Gaffiaya tetragena• Sarcinna: Cube like paket of 6 or 8 cocci, e.g; Sarcina lutea• Staphylococcus: Irregular bundle of cocci, e.g; Staphylococcus

aureus.

.• Baccilli:They are rod shaped bacteriaa) Streptobaccilli: Occur in chains, e.g; Bacillus subtilisb) Trichome: Chains of cell but have larger area of contact between

adjacent cells, e.g; saprospire species.

• Spirilla:• Vibrios: Comma shaped, e.g; Vibrio cholrae.• Spirilla: Spiral shaped, e.g; Tripone-pallidum• Spirochetes: Flexible cell wall but no fiagella, e.g; Triponea pallidum.• Filamantous: Actinomyces, Streptomyces

Bacterial Cells:

Bacterial Cell Structures1.     Capsules2.     Cell Wall3.     Plasma Membrane4.     Cytoplasm & Cytoplasmic Inclusions5.     Ribosomes6.     Bacterial DNA7.     Pili8.     Flagella9.     Spores

Capsules

• Many species of bacteria (bacilli & cocci) have a layer outside the cell wall which is designated as

• Microcapsule• Capsule• Loose slime according to their thickness,

composition & solubility.

.• Microcapsule:• It is relitively thin layer coposed of protein,

polysaccharides & lipids.

     Capsules

• It is thick viscous jelly like structure surrounding the cell.

• They are stained by –ve staining.• Structure

– Polysaccharide or polypeptide layer outside cell wall

– May be tightly or loosely bound – Detected by negative staining techniques

     Capsules (cont.)

• Functions :• It serve as buffer b/w cell and its external

environment.• They prevent the cell from dehydration.• They block attachment of bacteriophages.• They are involved in pathogenicity &

inhibit the engulfment of bacteria by WBC.

    Cell Wall• Gram Staining

– Method developed by Gram in 1888– Gram-positive cells stain purple

Gram-negative cells stain pink– Later, it was discovered that the major

factor determining Gram reactions is the bacterial cell wall structure

– “Gram-positive” & “Gram-negative”These terms can mean either:Staining results, or Types of cell wall structure

     Cell Wall• Peptidoglycan Structure

– Composition • A Polysaccharide • Composed of alternating units of

N-acetylglucosamine (NAG) andN-acetylmuramic acid (NAM)

– Peptide Crosslinking BetweenNAM units

– Much thicker and more crosslinking in Gram-positive than in Gram-negative Bacteria

     Cell Wall

• Gram-positive Cell Wall– Thick Layer of Highly Crosslinked

Peptidoglycan – Teichoic Acid Strands (Teichoic acids are

bacterial copolymers of glycerol phosphate or ribitol phosphate and carbohydrates linked via phosphodiester bonds.)

     Cell Wall• Gram-negative Cell Walls

– Outer Membrane • Lipopolysaccharide Layer

containing Lipid A • Phospholipid Layer • Outer Membrane Proteins

– Thin Layer of Peptidoglycanwith no teichoic acid

– Periplasmic Space

     Cell Wall

• Variations on Cell Wall Architecture– Acid-fast Cell Walls

• Similar to Gram-positive structure, buthave Mycolic Acid: A waxy lipid

• Require special acid-fast staining technique• Includes Mycobacterium and Nocardia

     Cell Wall• Variations on Cell Wall Architecture (cont.)

– Mycoplasmas• Bacteria that are naturally have no cell walls• Includes Mycoplasma and Ureaplasma

– Archaeobacteria• Have unusual archaeobacterial cell walls

with no peptidoglycan• Have unusual metabolisms• Share a more recent common ancestor with

eukaryotes than with eubacteria (“true bacteria”)

     Plasma Membrane

• Structure– Phospholipid Bilayer with Associated

Proteins

• Functions – Maintain Cell Integrity – Regulate Transport – Specialized Functions in Bacteria

Cytoplasm & Cytoplasmic Inclusions

• Composition: – Viscous aqueous suspension of proteins,

nucleic acid, dissolved organic compounds, mineral salts

• Cytoplasmic Inclusions:– Metachromatic Granules (Phosphate) – Starch Granules – Lipid Droplets – Sulfur Granules

     Ribosomes

• Suspended in Cytoplasm• Sites of Protein Synthesis

     Pili• Pilli are morphologically distinct nonfilagella

apendages found particularly in Gram negetive bacteria. They are 0.5-6um in length. No is 100- 400.

• Chemistry: They are compsed of protein pillin with

minimum molecular weight of about 17000.• Structure:• Pillis subunits are arranged in very precise helical

structure to form a smooth tube along a longitudinal hole.

.Function of Pilli:• one type called F-Pillus serve as a part of entry

of genetic material during bacterial conjugation• Other pilli play an important role in infection

by allowing the bacteria to attach to epithelial cells of host.

• Fimbriae:• They are sharp pilli. They help in attachment

to host cell.

     Flagella

• Function– Motility

Almost all motile bacteria are motile by means of flagella

– Motile vs. nonmotile bacteria

• Structure– Filament

Composed of the protein flagellin– Hook & Rotor Assembly

Permits rotational "spinning" movement

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Chemical Composition Chemical composition of basal body is

unknown. Hook and filament are composed of protein called Flagellin an elastic fibrous protein.

Origin of Flagella: the fact that flagella arise from the cytoplasm

was indicated by observation that protoplast of motile bacteria may still possess flagella. Their origin is apparently a granule (Bleopheroplast) within the plasma membrane.

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Location and NO Based on number & placement of flagella, bacteria

are divided into fillowing groups,• Monotrichous: having single flagella e.g; Pseudomonas aeruginosa, Vibrio cholrea• Lophotrichous: have group of two or more flagella at

one pole of the cell, e.g; pseudomonas fluorescens• Amphitrichous: have group of flagella at both ends,

e.g; Aquaspirillum serpens.• Peritrichous: whole covered with flagella e.g; Salmonella typhi.

     Flagella

• Mechanism of Motility– “Run and Tumble” Movement

controlled by the direction of the flagellar spin

– Counter clockwise spin = Straight RunClockwise spin = Random Tumble

     Flagella

• Chemotaxis– Response to the concentration of chemical

attractants and repellants– As a bacterium approaches an attractant:

the lengths of the straight runs increase– As a bacterium approaches a repellant:

the lengths of the straight runs decrease

Bacterial Spore• These are highly resistant bodies produced within the cells of certain

G+ve bacteria. They are produced under unfavourable conditions.

• Chemistry & Structure.• Endospores are spherical to elliptical in shape or simply spindle

shaped. They consist of central core of cytoplasm & nucleod surrounded by a membrane and then the spore wall.

• Around the spore wall, there is second layer called Cortex.• The cortex is surrounded by the internal & external layers.• Lastly the whole is enclosed by exosporium.• Cortex contain ‘Dipicolinic acid’ a special chemical constituent of

spore, responsible for remarkable resistant.

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Types of Spores: Various types of bacterial spores are

• Terminal: e.g; C.terminale• Sub- Terminal: e.g, C.subterminale• Central: e.g; Bacillus aerus.

   Bacterial Spores (Endospore)• Function

– To permit the organism to survive during conditions of desiccation, nutrient depletion, and waste buildup

– Bacterial spores are NOT a reproductive structure, like plant or fungal spores

• Occurrence – Produced by very few genera of bacteria – Major examplesBacillus Clostridium

     Spores

• Significance in Medicine & Industry – Spores are resistant to killing – Cannot be killed by 100°C (boiling) – Requires heating to 120°C for 15-20 min

(autoclaving or pressure cooking)

     Spores

• Sporulation – The process of spore formation – Governed by genetic mechanism – A copy of the bacterial chromosome is

surrounded by a thick, durable spore coat – This forms an endospore within a vegetative

cell – When the vegetative cell dies and ruptures,

the free spore is released

     Spores

• Spore Germination – When a spore encounters favorable growth

conditions – The spore coat ruptures and a new vegetative

cell is formed