Appendages – Flagella

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Appendages – Flagella

The structure of the bacterial flagella allows it to spin like a propeller and thereby propel the bacterial cell; clockwise or counter clockwise.

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

Appendages – Pili or Fimbriae

· Shorter than flagella and straighter , smaller.

· Made up of a protein called pilin.

· Only present on some gram- bacteria.

· Function: adhere, One of the invasive mechanism on bacteria.

· Some pathogens cause diseases due to this.

· In some bacteria, there is a special kind of pili called “sex pili” which is used for sexual reproduction.

· Origin: Cell membrane

Position:

— common pili , numerous over the cell, usually called fimbriae,

— sex pili, 1-4/cell

— Structure: composed of proteins which can be dissociated into smaller unit

Surface Layers – Capsule

— Capsules or slime layers are produced by most of the bacteria to surround their cells (a protective layer).

— It consists of polypeptide and polysaccharide in bacilli.

— Most of them have only polysaccharides.

Surface Layers – Cell Wall

The bacterial cell wall protects the cell protoplasm.

· is inert, rigid though elastic and gives a definite shape to the bacterial cell.

· It is made of mucopeptide, rather than cellulose and chitin, which are the constituents of plant and fungi cell walls.

· Mucopeptide is a polymer of alternating units of two amino sugars N-acetylgulcosamine and N-acetyl muramic acid.

· The cell wall is essential to the survival of many bacteria, and the antibiotic penicillin is able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan.

· Basically there are two types of cell walls present in bacteria, Gram + & Gram -.

· Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids.

· In contrast, Gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins.

· The majority of bacteria has a Gram – cell wall.

· The differences in the cell wall can determine how a particular bacteria responds to an antibiotic.

· For instance, vancomycin can kill only Gram-positive bacteria and is ineffective against Gram-negative pathogens, such as Haemophilus influenzae or Pseudomonas aeruginosa.