CHARACTERISTIC OF BACTERIAL CELLS

NING RINTISWATI2003

STRUCTURE OF BACTERIAL CELLS

BACTERIA ARE CLASSIFIED BY SHAPE into 3 basic group

cocci, bacilli and spirochaetes

Arrangement : diplococci

streptococci

staphylococci,etc

STRUCTUREs

CELL WALL

Multilayer, in external to cytoplasmic membrane

Composed of peptidoglycan which provides structural support and characteristic of shape of the cell

Cell wall of Gram positive and Gram negative bacteria

The peptidoglycan is much thicker than gram neg bacteria, some gram post also have teichoic acid outside the peptidoglycan

Gram neg organism have a complex outer layer of lipopolysaccharide, lipoprotein and phospholipid. Lying between the outer membrane layer and the cytoplasm membrane is the periplasmic space

CYTOPLASMIC MEMBRANE

COMPOSED OF PHOSPHOLIPID BILAYER SIMILAR WITH EUKARYOTIC CELLS

MAYOR FUNCTION:

- ACTIVE TRANSPORT OF MOL INTO THE CELL

- ENERGY GENERATION BY OXI DATIVE

PHOSPHORYLATION

- SYNTHESIS OF PRECURCOR THE CELL WALL

- SECRETION OF ENZYME AND TOXINS

MESOSOMEit is important in cell division as the origin of transverse septum that divides the cell in half

CYTOPLASMIC

- an amorphous matrix contains ribosome, nutrients granules,metabolites and ions

- an inner,nucleic region composed of DNA

RIBOSOMES70 S in size with 50S and 30S subunit

GRANULES

it is serve as storage areas of nutrients and stain characteristically by dyes. Ex: volutin is reserve of high energy stored in the form of polymerized metaphosphate.

PLASMIDS

Extrachromosomal

Double-stranded,circular DNA molecules

Capable to replicating independently of bact. chromosome

It can be integrated into bact. chromosome

TRANSMISSIBLE PLASMIDS

Can be transferred from cell to cell by conjugation

Large(MW 40-100 million)

Contain about a dozen genes responsible for synthesis of sex pilus and for enzymes required for transfer

Present in a few 1-3 copies per cell

NON TRANSMISSIBLE PLASMIDS

Are small (MW 3-20 million)

Do not contain of transfer genes

Frequently present in many(10-60)copies per cell.

Plasmids occur in gram pos and gram neg bacteria several different types can exist in one cell.Treatment with some compound can cure bacteria of their plasmid in vitro

The genes for following functions and structures are carried by plasmids:

Antibiotic resistance

Resistance to heavy metals

Resistance to UV light

Pili

Exotoxins including several enterotoxis

TRANSPOSONSAre pieces of DNA that move readily from one site to another site either within or between the DNA of bacteria, plasmids and bacteriophages.Are nicknamed ‘jumping genes”Can code for drugs resistance enzymes toxins,metabolic enzymesCause mutasions in the genes into which they insert or alte the expression of nearby genes

CAPSULES

Gelatinous layer covering the entire bacteriumComposed of polysaccharidesThere are 84 different sero-type of S.pneumoniae which are distinguish by antigenic difference of the sugars in the polysaccharide capsule

- Anthrax bacillus has a capsule of polymerized d-glutamic acid

CAPSULE IS IMPORTANT

Virulence factor for many bacteria: it limits the ability of phagocytes to engulf the bacteria.Variants of encapsulated bacteria that have lost the ability to produce a capsule are usually nonpathogenic

Specific identification of an organism can be made by using antiserum against the capsular polysaccharide

CAPSULES IS IMPORTANT

Capsular polysaccharides are uses as the antigens in certain vaccines,since they are capable of eliciting protective antibodies.

Role on adherence of bacteria to human tissues which is an important initial step causing infections

PILI (FIMBRIAE)

Hair like filament that extend from the cell surface

shorter and straighter than flagella and are

composed of subunits of protein, pilin, arranged in helical strands.

Are found mainly on gram negative bacteria

ROLES OF PILI

Attachment to a specific receptors on the human cell surface,which is a necessary step in the infection for some organisms.

Specialized kind of pilus (ex:sex pilus)

FLAGELLA

Are long, propel the bacteria toward food and other attractant, a process called chemotaxis

Composed of many subunits of a single protein: flagellin

The energy for movement :the proton motive force is provide by ATP

ROLES OF FLAGELLA

Provides move toward nutrients or away from harmful substances. This property (chemotaxis) is a function of sensors on the outer surface of the cell that detect differences of concentration of the medium

Are identified in clinical laboratory of specific antibodies against flagella protein

EDOSPORES

Highly resistant structures are formed in response to adverse conditionsIt is formed by genera Bacillus and ClostridiumSporulation occurs when nutrients are depletedExtraordinary resistant to heat and chemicals

ENDOSPORES

Sterilization cannot be achieved by boiling

Sterilization of products for medical use: Steam heating under pressure(autoclaving) at 121oC for 30 minutes

Spores are not seen in clinical specimen recovered from patients infected by spore-forming bacteria, since the supply of nutrients is adequate

ENDOSPORES

Endospore has no metabolic activity and can remain dormant for many years

Upon exposure by water and nutrients, specific enzyme degrade the coats, water and amterial enter and germination into metabolizing, reproducing bacterial cell occurs

One spore germinates into one cell

Bacterial structure

size:0.2 – 2 micron