GENERAL MICROBIOLOGY - T.P. Pyrog - 2004

5. STRUCTURE OF THE MICROBIAL CELL

5.5. DIFFERENCES BETWEEN PROKARYOTES AND EUKARYOTES

The structural, genetic, functional, and chemical differences between PROKARYOTES AND EUKARYOTES (summary data), as well as the Characteristic Features of gram-positive and gram-negative Bacteria (summary data), are presented in Tables 5.3–5.5.

Class="center">Table 5.3.

Structural and genetic differences between prokaryotes and eukaryotes

Organizational features	Prokaryotes	Eukaryotes
Structural differences
Enclosed secondary compartments formed by membranes	Absent	Present
Endoplasmic reticulum	Absent	Present
Size of cytoplasmic Ribosomes (sedimentation coefficient)	70S	80S
Size of Ribosomal RNAs (sedimentation coefficient)	5S; 16S; 23S	5S; 5,85S; 18S; 28S
Proportion of ribosomes associated with the cytoplasmic membrane	Observed	Absent
Cell/35.html">Mitochondria	Absent	Present
Organelles surrounded by a single protein membrane	Present	Absent
Golgi apparatus	Absent	Present
Nucleus	Nuclear analogue (nucleoid) present	Present
Nuclear membrane	Absent	Present
Vacuoles	Rare	Common
Flagella	Composed of one or several fibrils	Each flagellum consists of 20 fibrils arranged in a 2 x 9 + 2 pattern
Minimum cell dimension (width or diameter)	Typically 0.2-2.0 µm	Typically > 2.0 µm
Genetic differences
Organization of nuclear DNA	DNA is not separated from the Cytoplasm by a membrane	Enclosed in a nuclear envelope
Chromosome	Single circular (multiple copies may be present in The Cell)	More than one
Mitosis	Absent	Present
Meiosis	Absent	Present
Cytoplasmic DNA	Plasmids (not membrane-bound)	Mitochondria, METABOLISM/14.html">Chloroplasts, Golgi apparatus

Table 5.4.

Functional and chemical differences between prokaryotes and eukaryotes

Differences	Prokaryotes	Eukaryotes
Functional differences
Respiratory system	Associated with membranes or mesosomes	Localized in mitochondria—membrane-bound organelles
Chemolithotrophic metabolism	Present	Absent
Ability to fix molecular nitrogen	Present	Absent
Ability to perform dissimilatory nitrate reduction to nitrite and nitrogen gas	Present	Absent
Methanogenesis	Present	Absent
Anoxygenic Photosynthesis	Present	Absent
Anaerobiosis	Facultative and obligate	Facultative
Cytoplasmic streaming	Absent	Frequently observed
Phagocytosis	Absent	Present
Pinocytosis	Absent	Present
Intracellular Digestion	Absent	Present
Resistance to γ-irradiation	Very high	Low
Upper Temperature limit	75-90 °C	40-60 °C
Secretion of substances via Golgi vesicles	Absent	Present
Cellular endosymbionts	Absent	Present
Antibiotic sensitivity	Penicillins. Aminoglycosides. Tetracyclines. Macrolides	Polyenes. Glutarimides
Chemical differences
Peptidoglycans in The Cell wall	Present	Absent
Diaminopimelic acid in the cell wall	Present	Absent
Teichoic Acids in the cell wall	Present	Absent
Polyunsaturated Fatty acids in membranes	Rare	Present
Sterols in membranes	Absent	Present
Poly-β-hydroxybutyric acid (as a reserve material)	Present	Absent
DNA in organelles	Absent	Present

Table 5.5

Distinguishing features of gram-positive and gram-negative bacteria

Gram-positive bacteria	Gram-negative bacteria
Morphological features
Morphologically uniform: cocci, rods, toroidal, branched forms	Morphologically diverse: cocci, rods, toroidal, triangular, star-shaped, filamentous, helical, branched forms
Structural features
Single-layered cell wall	Double-layered cell wall comprising an inner rigid layer and an outer layer (outer membrane)
Cell wall thickness 20-80 nm, occasionally up to 100 nm	Rigid layer thickness 2-3 nm, outer membrane 8-10 nm
Homogeneous cell wall	Heterogeneous cell wall: dense rigid layer, outer membrane structurally similar to the cytoplasmic membrane
May form endospores, conidia	Endospores and conidia are absent. Some species can form exospores, myxospores, cysts
May possess aerial mycelium	Absent
Many species are non-motile	Most species are motile
Gliding motility absent	Possible
In motile forms, flagellation is peritrichous; polar is rare	Diverse flagellar arrangements
Prosthecae are generally rare	Prosthecae—thread-like extensions of the cell wall and membrane (1-2 per cell)—are found in many bacteria
Periplasmic space absent	Present
Carboxysomes absent	Present
Mesosomes present	Absent
Photosynthetic membrane apparatus absent	Present
Chemical features
Peptidoglycan is the main cell wall component, accounting for 50-80%, and sometimes up to 95%, of the total wall mass	The rigid layer contains 5-10% peptidoglycan by wall mass, and it is absent from the outer membrane. Walls lack peptidoglycan in Halococcus and Halobacterium
Meso-diaminopimelic acid is absent from peptidoglycan	Present
Gram-positive bacteria		Gram-negative bacteria
Cell walls contain acids (up to 50%)		Absent
Cell walls contain 3-4 types of Amino Acids		Contain 18-20 types of amino acids
Lipopolysaccharide absent from the cell wall		Present in the outer membrane
Lipoprotein absent from the cell wall		Always present in the outer membrane
Cell walls of most bacteria contain no Lipids (except Corynebacteria, Mycobacteria, Nocardia)		Contain lipids (up to 22%)
Physiological features
Mostly chemoheterotrophs		Many are chemoautotrophs
Photosynthesis absent		Possible
Lithoheterotrophy absent		Possible
Resistant to Proteolytic Enzymes (Trypsin, Pepsin)		Sensitive
Resistant to 1% KOH, NaOH, sodium azide, tellurium salts		Not resistant
Acid-fastness possible		Never acid-fast
Often unable to assimilate free amino acids		Capable of assimilation
Growth inhibited by iodine		Less sensitive to iodine
Produce exotoxins		Produce endotoxins
Autolysis is rare		Common
Living Cells are permeable to Dyes		Low permeability
Relatively resistant to high pressure and ultrasound		Low resistance
Low resistance to low surface tension		More resistant
Parasitism in bacterial cells, Protozoa, and animals absent		Possible

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