Bacterial Structure Beheshtimaal

Bacterial Morphology Arrangement1. Bacilli

a.Streptobacilli

b. Bacilli

2. Cocci

a. Cocci

b. Doplococci

c. Streptococci

d. Staphylococci

e. Sarcina ( 3D )

f. Gaffkya ( 2D ) 1Purvi Kakrani & Dr. Harish

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Common Shapes & Arrangement

2Purvi Kakrani & Dr. Harish

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Bacterial morphologies (1)


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Bacterial Morphology Arrangement

3 Spirl

a. Vibrio

b. Spirillum

c. Spirochete


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Bacterial Cell Structures & Functions


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Size relationships among prokaryotes


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Bacterial Cell Structure

Appendages - fdlagella, pili or fimbriae

Surface layers - capsule, cell wall, cell

membrane

Cytoplasm - nuclear material, ribosome,

mesosome, inclusions etc.

Special structure - endospore


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Bacterial Cell Structure


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Appendages

1. flagella

Some rods and spiral form have this.

a). function: motility

b). origin : cell membrane flagella attach to the

cell by hook and basal body which consists of set(s) of

rings and rods

Gram - : 2 sets of ring and rods, L, P, S, M rings and

rods

e.g. E. coli

Gram + : S, M rings and rods

e.g. B. megaterium12

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Organ of bacterial locomotion


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Structure of the flagellum


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Flagella movement(1)


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b).Origin (continued)

– The structure of the bacterial flagella allows it to spin

like a propeller and thereby propel the bacterial cell;

clockwise or counter clockwise ( Eucaryotic , wave

like motion.

– Bacterial flagella provides the bacterium with

mechanism for swimming toward or away from

chemical stimuli, a behavior is knows as

CHEMOTAXIX, chemosenors in the cell envelope

can detect certain chemicals and signal the flagella to

respond.


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c). position

monotrichous

lophotrichous

peritrichous

d). structure

protein in nature: subunit flagellin


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2. Pili or Fimbriae

Shorter than flagella and straighter , smaller.

Only on some gram- bacteria.

a). function: adhere. One of the invasive

mechanism on bacteria. Some pathogens

cause diseases due to this. If mutant

(fimbriae) not virulent. Prevent phagocytosis.


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pili - sex factor. If they make pili, they are + or

donors of F factor.

It is necessary for bacterial conjugation

resulting in the transfer of DNA from one cell to

another.

It have been implicated in the ability of

bacteria to recognize specific receptor sites on

the host cell membrane. In addition, number of

bacteria virus infect only those bacteria have F

pilus. 21Purvi Kakrani & Dr. Harish

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b). Origin: Cell membrane

c). Position: common pili , numerous over

the cell, usually called fimbriae sex pile, 1-

4/cell

d). Structure: composed of proteins which can

be dissociated into smaller unit

Pilin . It belongs to a class of protein Lectin

which bond to cell surface polysaccharide.22


II. CELL SURFACE LAYER

1. Capsule or slime layer

Many bacteria are able to secrete material that adheres to the bacterial cell but is actually external to the cell.

It consists of polypeptide and polysaccharide on bacilli. Most of them have only polysaccharide. It is a protective layer that resists host phagocytosis. Medically important.


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2. Bacterial Cell Wall

General structure: mucopolysaccharide i.e. peptidoglycan. It is made by N-acetylglucosamine and N-acetylmuramic acid. tetrapeptide ( L-alanine- isoglutamine-lysine-alanine) is attached. The entire cell wall structure is cross linked by covalent bonds. This provide the rigidity necessary to maintain the integrity of the cell.

N-acetylmuramic acid is unique to prokaryotic cell.


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Cell walls of bacteria(2)


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Structure of peptidoglycan(1)


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(a). Gram positive bacterial cell wall

Thick peptidoglycan layer

pentaglycin cross linkage.

Teichoic acid: ribitol TA &

glycerol TA

Some have peptioglycan

teichoic acid.

All have lipoteichoic acid. 31


Function of TA:

* Antigenic determinant

* Participate in the supply of Mg to

the cell by binding Mg++

* regulate normal cell division.

For most part, protein is not found as

a constituent of the G+ cell wall except

M protein on group streptococci


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Structure of the Gram-positive Cell Wall


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(b) Gram -

Thin peptidoglycan

Tetrapeptide cross linkage

A second membrane structure: protein and

lipopolysaccharide.

Toxicity : endotoxin on lipid A of

lipopolysaccharide. glucosamine- glucosamine-long

polysaccharide- repeated sequences of a few sugars

(e.g. gal- mann-rham) n=10-20 O antigen


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Toxicity : endotoxin on lipid A of

lipopolysaccharide.

glucosamine- glucosamine-long

FA FA FA FA

polysaccharide- repeated sequences of

a few sugars (e.g. gal- mann-rham)

n=10-20 O antigen36


Chemistry of LPS


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The Gram-negative outer membrane(1)


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The Gram-negative outer membrane(2)


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2. Cell Membrane

Function:

a. control permeability

b. transport e’s and protons for cellular metabolism

c. contain enzymes to synthesis and transport

cell wall substance and for metabolism

d. secret hydrolytic enzymes

e. regulate cell division. Fluid mosaic model. phospholipid bilayer and

protein (structure and enzymatic function). Similar to eukaryotic cell membrane but some differs. e.g. sterols such as cholesterol in Euk not in Prok. 40


The cytoplasmic membrane


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Functions of the cytoplasmic membrane(1)


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Functions of the cytoplasmic membrane(2)


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Transport proteins


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Classes of membrane transporting systems(1)


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III. Cytoplasm

80% water, nucleic acids, proteins, carbohydrates, lipid

and inorganic ions etc.

1. Bacterial chromosomes

a single large circular double stranded DNA no histone

proteins. The only proteins associated with the

bacterial chromosomes are the ones for DNA

replication, transcription etc.

2. Ribosome

protein synthesis 48


The bacterial chromosome and supercoiling


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3. Mesosomes

A large invaginations of the plasma membrane,

irregular in shape.

a. increase in membrane surface, which may be

useful as a site for enzyme activity in respiration

and transport.

b. may participate in cell replication by serving as a

place of attachment for the bacterial chromosome.


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4. Inclusions

Not separate by a membrane but distinct.

Granules of various kinds:

* glycogen,

*polyhydroxybutyric acid droplets (PHB)

i.e. fat droplets

* inorganic metaphosphate (metachromatic granules) - in

general, starvation of cell for almost any nutrients

leads to the formation of this to serve as an

intracellular phosphate reservoir.


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PHBPHB


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5. Chromatophores

Only in photosynthetic bacteria and blue green algae.

Prok. no chloroplast, pigment found in lamellae

located beneath the cell membrane.


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IV. Special Structure

* Endospores

Spore former: sporobactobacilli and sporosarcinae - no medical importance. bacillus and clostridium have medical importance.

* Position: median, sub-terminal and terminal have small water, high calcium content and dipicolinic acid (calcium dipicolinate)

extremely resistant to heat, UV, chemicals etc. may be due to many S containing A.A for disulfide groups.


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• After the active growth period approaching the stationary growth phase, a structure called forespore develops within the cells.

• It consists of coat, cortex and nuclear structure.

The process of endospore formation


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Endospores


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Negatively Stained Bacillus: (A) Vegetative Cell (B) Endospore


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Dipicolinic acid


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Vegetative/spore-containing cells(1)


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Vegetative/spore-containing cells(2)


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Detailed stepsin endospore formation(1)


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Bacterial Structure Beheshtimaal

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