bacteria caracteristic
TRANSCRIPT
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