Bacterial Morphology Arrangement Robert Hooke (1635-1703) English Scientist First to use the microscope to observe cells Coined the term “cell”

Bacterial Morphology Arrangement

Robert Hooke (1635-1703) English Scientist First to use the

microscope to observe cells

Coined the term “cell”

Anton van Leeuwenhoek1632-1723

Dutch scientist Invented the first

compound microscope First to observe

LIVING cells Blood cells and

protists

Robert Brown1773-1858 Scottish botanist In 1831 he was the

first person to observe the nucleus of a cell

Schleiden & Schwann1804-1881 1810-1882

Developing Cell Theory 1838

SchleidenSaid “all plants

are made up of cells”

SchwannSaid “all animals

are made up of cells”

Cell Theory Overview

1. All organisms are made of one or more cells [Unicellular or Multicellular].

2. All cells carry on life activities.

3. New cells arise only from other living cells.

Prokaryotic vs Eukaryotic PROKARYOTIC Simplest form Lack membrane

bound structures Lack true nucleus Example: bacteria

and cyanobacteria

EUKARYOTIC Most common Possess membrane

bound structures and a nucleus

Found in most living things

Sizes of Cells Eukaryotic are

usually larger than prokaryotic

Both nutrients and wastes are constantly entering and exiting cells

Vary in size and shape

Size relationships among prokaryotes

Bacterial Morphology Arrangement1. Rod or Bacilli

a.Streptobacilli

b. Bacilli

2. Cocci

a. Cocci

b. Diplococci ( e.g. Neisseria meningitidis)

c. Streptococci ( e.g. Streptococcus pyogenes)

d. Staphylococci (e.g. Staphylococcus aureus)

e. Sarcina

f. tetrads ( Micrococcus species)

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Bacterial Shapes, Arrangements, and Sizes

Variety in shape, size, and arrangement but typically described by one of three basic shapes: coccus - spherical bacillus – rod

coccobacillus – very short and plump ( Brucella abortus) Streptobacilli ( Bacillus subtilus) diplobacilli

spirillum - helical, comma, twisted rod, spirochete – spring-like- flexible ( Treponema pallidum) vibrio – gently curved ( Vibrio cholera) Spirilla- rigid ( Borrelia species)

Pleomorphic : variable in shape ( Corynebacterium)

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Bacterial Shapes, Arrangements, and Sizes Arrangement of cells is dependent on pattern of

division and how cells remain attached after division: cocci:

singles diplococci – in pairs tetrads – groups of four irregular clusters chains cubical packets

bacilli: chains palisades

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Streptococcus sp.

Bacterial morphologies (1)

Bacterial morphologies (2)

Bacterial morphologies (3)

Bacterial Morphology Arrangement

3 Spirl

a. Vibrio

b. Spirillum

c. Spirochete

Bacterial morphologies (4)

Borrelia (spirochete)

Bacterial Cell Structures & Functions

Pili

Bacterial Cell Structure

Appendages - flagella, pili or fimbriae

Surface layers - capsule, cell wall, cell

membrane

Cytoplasm - nuclear material, ribosome,

mesosome, inclusions etc.

Special structure - endospore

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. megaterium

FlagellaMotility - movementSwarming occurs with some bacteria

Spread across Petri Dish Proteus species most evident

Arrangement basis for classification Monotrichous; 1 flagella Lophotrichous; tuft at one end Kophotrichous; tuft at both ends Amphitrichous; both ends Peritrichous; all around bacteria

Structure of the flagellum

c).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 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.d). structure

protein in nature: subunit flagellin ( globular protein)

Flagella movement(1)

Flagella movement(2)

2. Fimbriae and Pili

Fimbriae: Shorter than flagella and

straighter , smaller, hairlike appendages . Only

on some gram- bacteria.

a). function: adhere. Not involve in motility.

One of the invasive mechanism on bacteria.

Some pathogens cause diseases due to this

(Antigenic characteristic). Prevent phagocytosis.

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.

Conjugation in E. coli

b). Origin: Cell membrane

c). Position: common pili , numerous over

the cell, usually called 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.

II. CELL SURFACE LAYER

1. Glycocalyx: 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 ( Streptococcus pneumonia).

Capsule and Slime layer The layer is well organized and not easily washed off,

it is capsule Slime layer, unorganized material that is easily

removed. They give mucoid growth on agar plate B. anthracis has a capsule of poly-D-glutamic acid,

while S. pyogenes made of Hyaluronic acid. Function: Resistant phagocytosis, Protect against

desiccation, Attachment to surface of solid objects.

Axial FilamentsPresent in spirochetes ( Treponema

pallidum cause syphilis)Function is motility – gliding motilityBundles of fibrils that arise at the ends

of the cell

SpirochetesAxial filamentStructurally similar to flagellaUnique location under an outer

membrane

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.

Cell walls of bacteria(2)

Cell walls of bacteria(3)

Cell walls of bacteria(4)

Cell walls of bacteria(1)

Structure of peptidoglycan(1)

Structure of peptidoglycan(2)

a). Gram positive bacterial cell wall

Thick peptidoglycan layer

pentaglycin cross linkage.

Teichoic acid (TA): Polymer of ribitol

& glycerol joined by phosphate

groups

Some have peptioglycan teichoic acid.

All have lipoteichoic acid.

Function of Teichoic acids:

* 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

Structure of the Gram-positive Cell Wall

(b) Gram negative bacterial cell wall:

Thin peptidoglycan

Tetrapeptide cross linkage

A second membrane structure: protein and

lipopolysaccharide (LPS).

Toxicity : endotoxin on lipid A of LPS.

glucosamine- glucosamine-long

polysaccharide- repeated sequences of a few sugars

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

Structure of peptidoglycan(3)

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 antigen

Chemistry of LPS

The Gram-negative outer membrane(1)

The Gram-negative outer membrane(2)

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Atypical Cell Walls Some bacterial groups lack typical cell wall

structure i.e. Mycobacterium and Nocardia Gram-positive cell wall structure with lipid mycolic

acid (cord factor) pathogenicity and high degree of resistance to certain

chemicals and dyes basis for acid-fast stain used for diagnosis of infections

caused by these microorganisms

Some have no cell wall i.e. Mycoplasma cell wall is stabilized by sterols pleomorphic

2. Cell Membrane

Function:

a. control permeability

b. transporte’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.

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Functions of the cytoplasmic membrane(1)

Functions of the cytoplasmic membrane(2)

Transport proteins

Classes of membrane transporting systems(1)

Classes of membrane transporting systems(2)

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Bacterial Internal Structures

Cell cytoplasm: dense gelatinous solution of sugars, amino

acids, and salts 70-80% water

serves as solvent for materials used in all cell functions

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Bacterial Internal StructuresChromosome

single, circular, double-stranded DNA molecule that contains all the genetic information required by a cell

DNA is tightly coiled around a protein, aggregated in a dense area called the nucleoid.

The bacterial chromosome and supercoiling

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Bacterial Internal StructuresPlasmids

small circular, double-stranded DNA free or integrated into the chromosome duplicated and passed on to offspring not essential to bacterial growth and

metabolism may encode antibiotic resistance, tolerance to

toxic metals, enzymes and toxins used in genetic engineering- readily

manipulated and transferred from cell to cell

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Bacterial Internal Structures

Ribosomes (70 S) made of 60% ribosomal RNA and 40%

protein consist of two subunits: large and small procaryotic differ from eucaryotic

ribosomes in size and number of proteins site of protein synthesis present in all cells

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3. Mesosomes ( mostly in Gram +ve)

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.

4. Inclusions

Not separate by a membrane but distinct.

Granules of various kinds:

* glycogen ( used as carbon source),

*polyhydroxybutyric acid droplets (PHB)

i.e. fat droplets and have Lipid inclusion

* inorganic metaphosphate (metachromatic granules or

Volutin granules) - in general, starvation of cell for almost

any nutrients leads to the formation of this to serve as an

intracellular phosphate reservoir ( Corynebacterium).

PHBPHB

5. Chromatophores

Only in photosynthetic bacteria and blue green algae. Prok.

no chloroplast, pigment found in lamellae located beneath

the cell membrane.

Sulfur Granules: Mainly in Thiobacillus, convert H2S to S

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IV. Special Structure

* Endospores

Spore former: Sporobactobacilli and Sporosarcinae (Gram + cocci)- no medical importance.

Bacillus and Clostridium ( Gram + Rod) have medical importance. Coxiella ( Gram –ve Rod) cause Q fever.

* 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.

• 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

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

Dipicolinic acid

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Detailed stepsin endospore formation(1)

Detailed stepsin endospore formation(2)

Detailed stepsin endospore formation(3)

PROCARYOTIC vs. PROCARYOTIC vs. EUCARYOTIC CELLSEUCARYOTIC CELLSProperty Procaryotes Eucaryotes

Membrane-bound nucleus Absent Present

DNA complexed with histones No Yes

Number of chromosomes One > One

Nucleolus Absent Present

Mitosis No Yes

Genetic recombination Partial Meiosis

unidirectional f usion of gametes

PROCARYOTIC vs. PROCARYOTIC vs. EUCARYOTIC CELLSEUCARYOTIC CELLSProperty ProcaryotesEucaryotes

Mitochondria Absent Present

Chloroplasts Absent Present

Endoplasmic reticulum Absent Present

Golgi apparatus Absent Present

PROCARYOTIC vs. PROCARYOTIC vs. EUCARYOTIC CELLSEUCARYOTIC CELLSProperty Procaryotes Eucaryotes

Plasma membrane sterols Usually no Yes

Flagella Submicroscopic Membrane bound

(1 fi ber) 20 microtubules

(9+2)

Microtubules Absent or rare Present

PROCARYOTIC vs. PROCARYOTIC vs. EUCARYOTIC CELLSEUCARYOTIC CELLS

Property Procaryotes Eucaryotes

70S (30S+50S)

80S (40S+60S)

Lysosomes, peroxisomes Absent Present

Cell walls

Ribosomes

Complex; peptidoglycan Simple; no peptidoglycan

70S (30S+50S)