Anatomy and physiology of bacteria

Anatomy and Anatomy and physiology of bacteriaphysiology of bacteria

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UNIVERSITY OF UNIVERSITY OF SOMALIA (UNISO)SOMALIA (UNISO)

INTRODUCTIONINTRODUCTIONAll living cells can be classified into

two groups,ProkaryotesEukaryotes

Prokaryotes are structurally simpler and smaller than eukaryotes.

Prokaryotes cellsBacteria , Archaea

Eukaryotic cells.Plants ,animalsFungi (yeasts and molds),Protozoa, algae

INTRODUCTIONINTRODUCTION

Distinguishing characteristics of Distinguishing characteristics of prokaryotesprokaryotes

1. Their DNANot enclosed by a membraneSingular, circular chromosome

2. Their DNA is without histones

3. They lack membrane-enclosed organelles.

Distinguishing characteristics of Distinguishing characteristics of prokaryotesprokaryotes

4. Their cell walls contain the polysaccharide peptidoglycan.

5. They divide by binary fission. The DNA is copiedThe cell splits into two cells.

Prokaryotes = (from the Greek, meaning prenucleus)

Distinguishing characteristics of Distinguishing characteristics of eukaryoteseukaryotes

1. Their dnaFound in the cell’s nucleusSeparated from the cytoplasm by a nuclear membrane

Linear , multiple chromosomes

2. Their dna is associated with proteins called histones

Distinguishing characteristics Distinguishing characteristics of eukaryotesof eukaryotes3. They have a number of

membrane-enclosed organelles, including

1. Mitochondria2. Endoplasmic reticulum3. Golgi complex4. Lysosomes

4. Their cell walls, when present, are chemically simple.

5. Cell division involves mitosis

Eukaryote = from the Greek, meaning true nucleus

Distinguishing characteristics Distinguishing characteristics of eukaryotesof eukaryotes

CHECK YOUR UNDERSTANDING

Q1: What is the main feature that distinguishes prokaryotes from eukaryotes?

THE PROKARYOTIC CELLTHE PROKARYOTIC CELLVery small unicellular organisms

Prokaryotes include bacteria and archaea

The majority of prokaryotes are bacteria.

The species of bacteria are differentiated by many factors

a. Morphology (shape)b. Chemical composition (by

staining)c. Nutritional requirementsd. Biochemical activitiese. Sources of energy (sunlight or

chemicals).12

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External External StructuresStructures

Glycocalyx

Flagellum

Axial filaments

Fimbria

Pilus

The Size, Shape, and Arrangement of The Size, Shape, and Arrangement of Bacterial CellsBacterial Cells

Most bacteria range from 0.2 to 2.0 mμ in diameter and from 2 to 8 m in lengthμ

Bacterial basic shapes:

Coccus: (plural: cocci ) sphericalBacillus: (plural: bacilli) : rod-shaped

Spiral: hire-like

The Size, Shape, and Arrangement The Size, Shape, and Arrangement of Bacterial Cellsof Bacterial Cells

A) Cocci: Usually round or ovalElongatedFlattened on one side.

When cocci divide to reproduce, the cells can remain attached to one another.

The Size, Shape, and The Size, Shape, and Arrangement of Bacterial CellsArrangement of Bacterial Cells

Cocci that remain in pairs after dividing are called diplococci

Cocci that remain attached in chainlike patterns are called streptococci

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Cocci that divide in two planes and remain in groups of four are known as Tetrads

Cocci that divide in three planes and remain attached in cube-like groups of eight are called Sarcinae

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Cocci that divide in multiple planes and form grapelike clusters are called staphylococci


What is the medical What is the medical importance of theses cell importance of theses cell arrangements????arrangements????

helpful in identifying certain cocci bacteria!

This gives the likely diagnosis for the disease 29

◦B) Bacilli Single bacilli: most bacteria appear as single rods

Diplobacilli : appear in pairs after division

Streptobacilli: occur in chainsCoccobacilli : oval and look like cocci

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The Size, Shape, and The Size, Shape, and Arrangement of Bacterial CellsArrangement of Bacterial Cells

C) Spiral bacteria have one or more twists; they are never straight. Vibrios: Bacteria that look like curved rods

Spirilla: have a helical shape, like a corkscrew, and fairly rigid bodies.

spirochetes: spiral which are helical and flexible

The Size, Shape, and Arrangement of The Size, Shape, and Arrangement of Bacterial CellsBacterial Cells

Cocci, bacilli, and spirilla use flagella to move

spirochetes move by means of axial filaments

Resemble flagella but are contained within a flexible external sheath.

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CHECK YOUR UNDERSTANDINGCHECK YOUR UNDERSTANDING

How would you be able to identify streptococci through a microscope?

Why don’t bacilli form tetrads or clusters?


How do the planes of division determine the arrangement of cells?


What is the distinguishing feature of spirochete bacteria?


GlycocalyxGlycocalyxFound on external surface layer of some

bacteria Composed of sticky polysaccharides,

polypeptide, or bothTwo forms:Capsule:

Well organized Firmly attached to cell wall

Slime layer: Unorganized Loosely attached

Capsule Capsule of of bacteriabacteria

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Glycocalyx (capsule)Glycocalyx (capsule)

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1. Allows cells to attach → key to biofilm formation

2. Prevents phagocytosis → virulence factor

3. protect against dehydration.4. Its viscosity: inhibit the movement of

nutrients out of the cell.

E.g.: Bacillus anthracis, Streptococcus pneumoniae,

Streptococcus mutans

Flagellum – FlagellaFlagellum – FlagellaAre long filamentous appendages that move

bacteria (Motility)Attached to the cell wall and cell membrane

Flagella arrangements: Atrichous: Bacteria that lack flagella. (no

flagella) Monotrichous: a single flagellum at one

pole

Peritrichous: Flagella distributed over the entire cell

Lophotrichous: a tuft of flagella coming from one pole

Amphitrichous: flagella at both poles of the cell

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Flagellum – FlagellaFlagellum – Flagella

___________

_______

Flagellar ArrangementFlagellar Arrangement

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A flagellum has three basic parts 1.the filament, 2.the hook3.the basal body

MotilityMotility

Due to rotation of flagella

Mechanism of rotation: “Run and tumble”

Move toward or away from stimuli (taxis)

Chemotaxis , phototaxis magnetotaxis

Flagella proteins are H antigens (e.g., E. coli O157:H7)

Moving by flagellaMoving by flagella

““Run and Tumble”Run and Tumble”

Fig 4.9

Axial FilamentsAxial Filaments

Endoflagella

In spirochetes only

Anchored at one end of a cell

Rotation causes cell

to move

Fimbriae allow attachment

Pili are used to transfer DNA from one cell to another

Fimbriae and Pili

FimbriaeFimbriaeFor example, fimbriae on the

bacterium Neisseria gonorrhoeae the causative agent of gonorrhea, help the microbe colonize mucous membranes.

Once colonization occurs, the bacteria can cause disease.

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FimbriaeFimbriaeThe fimbriae of E. coli O157 enable this

bacterium to adhere to the lining of the small intestine, where it causes a severe watery diarrhea.

When fimbriae are absent (because of genetic mutation), colonization cannot happen, and no disease develops

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PiliPililonger than fimbriae only one or two per cell. Pili function in motility and DNA

transfersex pili are used to bring bacteria

together allowing thetransfer of DNA from one cell to

another, a process called conjugation51

Why DNA is transferred between Why DNA is transferred between two bacteria??? What is the two bacteria??? What is the advantage??advantage??

The exchanged DNA can add a new function to the recipient cell such as:

a.Antibiotic resistance b.The ability to digest its medium

more efficiently52

Cell WallCell WallRigid for shape & protection

⇒ prevents osmotic lysis

Consists of Peptidoglycan (murein) → polymer of 2 monosaccharide subunits ◦ N-acetylglucosamine (NAG) and ◦ N-acetylmuramic acid (NAM)

Functions of cell wallFunctions of cell wall

1. Surrounds the the fragile plasma membrane gives the bacteria shape and protection

2. prevent bacterial cells from osmotic lysis3. Contributes to the ability of some species

to cause disease 4. It’s site of action of some antibiotics5. Differentiate major types of bacteria.

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Fig 4.13

Linked by polypeptides (forming peptide cross bridges) with tetrapeptide side chain attached to NAM

Gram + Gram + Cell WallCell Wall

Thick peptidoglycan

Negatively charged Teichoic acid on surface

Thin peptidoglycan

Outer membrane

Periplasmic space

Gram – Cell Wall

Fig.4.13b

Gram-Positive Cell WallsGram-Positive Cell Walls

Teichoic acidsMay regulate movement of cations

Polysaccharides: provide antigenic variation

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60Cell wall of gram positive bacteria

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Cell wall of gram negative bacteria

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1- Lipid A: of LPS acts as endotoxin

Lipid A responsible for the symptoms associated with infections by gram-negative bacteria,such as:

• fever•dilation of blood vessels•Shock•blood clotting.

Gram-negative Cell WallGram-negative Cell Wall

2- The core polysaccharide: role is structural—provide stability 3- O polysaccharides functionsas an antigen and is useful for distinguishing species of gramnegativebacteria, e.g., E. coli O157:H7

LPS layer = outer layer of outer membrane

Gram neg. bacteria are less sensitive to medications??? Why????

Because the outer membrane acts as additional barrier !

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Gram-negative Cell WallGram-negative Cell Wall

Gram Stain MechanismGram Stain MechanismCrystal violet-iodine crystals form in

cell.

Gram-positive

◦ Alcohol dehydrates peptidoglycan

◦ CV-I crystals do not leave

Gram-negative

◦ Alcohol dissolves outer membrane and leaves holes in peptidoglycan.

◦ CV-I washes out

Bacteria with No Cell Wall: MycoplasmasBacteria with No Cell Wall: Mycoplasmas

Instead, have cell membrane with cholesterol compounds (sterols), similar to eukaryotic cells

Cannot be detected by typical light microscopy

This EM shows some typically pleomorphic mycoplasmas

Acid-fast Cell Acid-fast Cell WallsWalls

Genus Mycobacterium and Nocardia

mycolic acid (waxy lipid) covers thin peptidoglycan layer

Do not stain well with Gram stain → use acid-fast stain

Damage to Cell WallDamage to Cell WallLysozyme digests

disaccharide in peptidoglycan.

Penicillin inhibits peptide bridges in peptidoglycan.

Internal Structures: Internal Structures: Cell MembraneCell Membrane

Analogous to eukaryotic cell membrane:Phospholipid bilayer with proteins

(Fluid mosaic model)

Permeability barrier (selectively permeable)

Diffusion, osmosis and transport systems

Internal Structures: Internal Structures: Cell MembraneCell Membrane

Different from eukaryotic cell membrane:Role in Energy transformation

(electron transport chain for ATP production)

Damage to the membrane by alcohols, quaternary ammonium (detergents), and antibiotics causes leakage of cell contents.

Fig 4.14

Cytoplasm and Internal StructuresCytoplasm and Internal Structures

Location of most biochemical activitiesNucleoid: nuclear region containing

DNA (up to 3500 genes). Difference between human and bacterial chromosome?

Plasmids: small, nonessential, circular DNA (5-100 genes); replicate independently

Ribosomes (70S vs. 80S)

Inclusion bodies: granules containing nutrients, monomers, Fe compounds (magnetosomes)

EndosporesEndosporesDormant, tough, non-reproductive

structure; → germination → vegetative cells

Spore forming genera: __________?

Resistance to UV and γ radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants

Relationship to disease

Sporulation: Endospore formation

Germination: Return to vegetative state

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EndosporesEndospores

Sporulation Sporulation

•Green endospores within pink bacilli•Many spores have already been released from the vegetative cells

Health & Medicine

Anatomy and physiology of bacteria