Download PROKARYTOTES EUKARYOTES

PROKARYTOTES
Domain Bacteria
Domain Archea
EUKARYOTES
Domain Eukarya
Fig. 1. The three domains of life.
Table 1. Major Differentiating Characteristics of Bacteria and Eukaryotic Cells
Characteristic
Bacteria (Prokaryotes)
Eukaryotes
Size (diameter)
1-5 m
10-100 m
Chromosomes
One (circular)
Two or more
Introns (non-coding parts of genes)
Absent
Present
Nuclear membrane
Absent
Present
Cell division
By binary fission
By mitosis (or meiosis)
Membranous organelle
Absent
Present
(mitochondria, ER, Golgi, lysosomes,
chloroplasts, peroxisomes)
Ribosome size
70 S
80 S
Peptidoglycan cell walls
Present
Absent
Sterols in membrane
Absent
Present
Flagella
Basal body/hook/filament;
Microtubules (9 + 2);
flagellum rotation
flagellum undulation
Fig. 3. The Gram Stain
Colour of the cells
--------------------------------------Gram +ve
Gram -ve
1. Bacterial are treated with primary stain, crystal violet
2. Cells are treated with mordant stain, potassium iodide
and iodine, which forms a complex with the crystal violet
3. Cells are decolourised by brief treatment with ethanol. Gram +ve
cells but not Gram –ve cells retain some of the crystal violet-iodine
complex due to a thicker cell wall (peptidoglycan).
4. Cells are counterstained with a red dye, carbol fuschin. Gram –ve
cells stain red whereas Gram +ve cells retain their purple colour.
N.B. As cultures age, Gram +ve cells often become Gram -ve due to wall deterioration.
Table 2. General characteristics of selected pathogens
Bacteria
Shape
Gram
Motile Spores
Staphylococcus aureus
Coccus +ve
No
No
Streptococcus pyogenes
Coccus +ve
No
No
Bacillus anthracis
Rod
+ve
No
Yes
Clostridium tetani
Rod
+ve
Yes
Yes
Diseases caused
Superficial and invasive infections
Superficial and invasive infections
Anthrax
Tetanus
Escherichia coli
Pseudomonas aeruginosa
Vibrio cholera
Salmonella enterica
Neisseria meningitidis
Bordetella pertussis
Legionella pneumophila
Treponema pallidum
Diarrhoea; meningitis
Opportunistic pathogen
Cholera
Gastroenteritis
Meningitis
Whooping cough
Legionnaire’s disease (pneumonia)
Syphilis
Rod
Rod
Rod
Rod
Coccus
Rod
Rod
Helical
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
Yes
Yes
Yes
Yes
No
No
Yes
Yes
No
No
No
No
No
No
No
No
THE BACTERIAL CYTOPLASM
COMPOSITION
Water ( 70-80%), Nucleic acids (DNA & RNA), Proteins, Carbohydrate, Low-Mr
compounds, inorganic ions.
STRUCTURES PRESENT
Bacterial Chromosome: single long circular double-stranded helical DNA molecule ( 4 x 106
base pairs [4 mega base pairs] in length), tightly wound as supercoils. The hereditary information
defining the cell’s structures and functions. N.B. Absence of a nuclear membrane.
Plasmids: Extrachromosal small circular independently replicating double-stranded DNA
molecules often encoding features which enhance the survival of organisms in a particular
environment e.g. virulence factors.
Ribosomes: 70S in size (cf 80S in eukaryotes), composed of small 30S subunit and large 50S
subunit; site of protein synthesis.
Cytoplasmic Inclusion Bodies: Granules/globules usually contain storage material (energy
reserve) in polymerised form e.g. starch, glycogen, polyhydroxybutyric acid, sulphur, and
polyphoshate (metachromatic or volutin granules).
Specialized Inclusion Bodies: Gas vesicles (buoyancy in aquatic bacteria); magetosomes (iron
oxide deposits acting as bar magnets and allowing bacteria to orient and move along geomagnetic
field lines.)
FUNCTIONS
Houses cell’s hereditary information
Genome replication
Synthesis of DNA and RNA
Synthesis of proteins
Generation of ATP by oxidation of glucose and other C-sources (glycolysis, citric acid cycle)
Early stages of peptidoglycan biosynthesis (synthesis of peptidoglycan building blocks)
Numerous other “housekeeping” and regulatory activities
Fig. 21. Right: DNA strands released from a lysed bacterial cell. Left: Poly- -hydroxybutyrate
granules in Rhodovibrio sodomensis.
BACTERIAL ENDOSPORE
PRINCIPAL GENERA: Bacillus (aerobe) and Clostridium (obligate anaerobe)
Table 4. Major Differences between Endospores and Vegetative Cells
Characteristic
Structure
Vegetative Cell
Typical
Microscopic appearance
Enzyme activity, metabolism, biosynthesis
mRNA
Heat resistance
Chemical & radiation resistance
Lysozyme resistance
Calcium content
Dipicolinic acid content
Small acid soluble spore proteins
Cytoplasmic pH
Nonrefractile
High
Present
Low
Low
Low
Low
Absent
Absent
About pH 7
Endospore
Distinct & complex; thick spore
cortex, spore coat; exosporium
Refractile
Low or absent
Low or absent
High (killed at 121 oC 15 min)
High
High
High
Present
Present
About pH 5.5-6.0
IMPORTANT SPORE-FORMING PATHOGENS: B. anthracis (anthrax; germ warfare
agent);
B. thuringiensis (insect pathogen producing toxic crystals); Cl. botulinum (food poisoning botulism); Cl. tetani (tetanus); Cl. perfringens (food poisoning; gas gangrene).
SPORULATION CYCLE:
Sporulation – exhaustion of an essential nutrient (e.g. C or N source); spore formation
Dormancy – cryptobiotic (no metabolic activity yet potential viable) for many thousands of
years
Activation – usually by heat or mechanical forces; presence of essential nutrients
Germination – water , spore swelling; loss of cortex, DPA & resistance to heat &
chemicals
Outgrowth – synthesis of new RNA, DNA and protein; formation of vegetative cell