is occupied by chromatin, entanglement of double-stranded
DNA molecules associated with proteins, histones. The
chromosomes become visible at the time of cell division.
In the middle of the chromatin, usually a single nucleolus is
the location of the synthesis of ribosomal RNA.
The soluble portion of cytoplasm or cytosol contains a set
of microfilaments and microtubules (cytoskeleton), involved
in maintaining cell shape, intracellular movements, cell
locomotion by forming pseudopods, and cellular exchanges
(endocytosis and exocytosis). Many inclusions (droplets of
lipids, polysaccharide reserve) and many organelles are
located in the cytosol (Table 3.2). Some organelles are
formed by double-layer phospholipid membrane,
delineating compartments of various shapes (vesicles,
tubules, lamellae, etc.). Among these organelles, some are
limited by a single membrane (endoplasmic reticulum, Golgi
apparatus, lysosomes, peroxisomes), others by a double
membrane (mitochondria and chloroplasts). There are also
organelles composed of proteins: centriole, centrosome,
ribosomes (RNAs and proteins), cilia, flagella (undulipodia),
and proteasomes. Mitochondria and chloroplasts (plants),
organelles of the same size as bacteria, have the particularity
to contain DNA bacterial type (cf. Sects. 4.3.1 and 5.4.2).
They multiply independently of the host cell. The
amyloplasts of plants are specialized in synthesis and accumulation of starch. The presence of organelles and their
importance in eukaryotic cells depends on the types of
microorganisms and cellular activity.
Some eukaryotic microorganisms have a filamentous
vegetative apparatus (Fungi). According to the taxa, these
filaments are consisting of cells or a mass of multinucleated
cytoplasm (syncytium). It may also be alternating between a
single-cell generation and a filamentous generation (cf. Sect.
7.14.3).
3.2
Concept of Metabolism
The maintenance of cellular integrity, growth, and reproduction of living organisms requires the synthesis of cellular
material, which depends on nutrients entering the interior of
cells and subjected to a series of chemical changes. The sum
of these changes is responsible for the production of energy
(catabolism) and synthesis of biomolecules (anabolism); it is
the metabolism of the cell (Fig. 3.7). Metabolic reactions are
catalyzed by enzymes that, by combining with the biological
molecules, decrease the activation energy of reactions and
determine the reaction pathway to be used for the transformation of substances.
As sources of energy, the nutrient is oxidized, and the
energy produced during the oxidation is transferred as
energy-rich compounds, mostly in the form of ATP. These
reactions of oxidation or degradation are the cellular
catabolism:
1. In general, energy sources are organic compounds
(chemoorganotrophic microorganisms*).
The oxidation of organic compounds can be partial or
complete. When it is partial, the organic molecules of
small molecular weight are produced, more oxidized than
organic sources given as nutrients. The complete
Table 3.2 Characteristic organelles of eukaryotic cells
Organelles
Description
Function
Endoplasmic
reticulum (ER)
Flattened cavities (limited by smooth membranes or membranes
covered with ribosomes) and vesicles
Synthesis of glycoproteins, lipids, sterols; transport
of various substances
Ribosomes
80 S particles formed of two subunits of 40S and 60S
Synthesis of proteins, forming polysomes if arranged
in chains fixed to mRNA
Golgi apparatus
(GA)
Pile of flattened sacs formed from vesicles, derived from ER
Finishing synthesis (proteins), packaging, and secreting of
various cellular substances (lysosomes)
Lysosomes
Set of vesicles from the ER and GA
Containing hydrolytic enzymes, digestion of substrates
Vacuoles
Origin: ER and GA; large size in plant cells
Contractile vacuoles, digestive vacuoles; sequestration and
storage of substances; hydric balance of plant cells
Peroxisomes
Vesicles formed from the ER
Containing redox enzymes
Proteasome
Enzymatic complex
Digestion of endogenous proteins; regulation of enzyme
activity
Mitochondria
Rod about 2–3 μm long, double membrane with folded inner
membrane; containing DNA of prokaryotic type
Respiratory center of the cell, respiratory transporters,
and enzymes included in the inner membrane
Chloroplasts
Various lamellar structures (thylakoids); containing DNA
of prokaryotic type
Containing the photosynthetic pigments, photosynthesis
Centrioles
Formed by the association of microtubules
Formation of the centrosome; participate in the formation
of undulipodia
Centrosome
Formed from centrioles
Intracellular movements
Undulipodia
Cytoplasmic expansions containing microtubules inserted
on basal granules (kinetosomes)
Cellular movements
3 Structure and Functions of Microorganisms: Production and Use of Material and Energy
33
DNA molecules associated with proteins, histones. The
chromosomes become visible at the time of cell division.
In the middle of the chromatin, usually a single nucleolus is
the location of the synthesis of ribosomal RNA.
The soluble portion of cytoplasm or cytosol contains a set
of microfilaments and microtubules (cytoskeleton), involved
in maintaining cell shape, intracellular movements, cell
locomotion by forming pseudopods, and cellular exchanges
(endocytosis and exocytosis). Many inclusions (droplets of
lipids, polysaccharide reserve) and many organelles are
located in the cytosol (Table 3.2). Some organelles are
formed by double-layer phospholipid membrane,
delineating compartments of various shapes (vesicles,
tubules, lamellae, etc.). Among these organelles, some are
limited by a single membrane (endoplasmic reticulum, Golgi
apparatus, lysosomes, peroxisomes), others by a double
membrane (mitochondria and chloroplasts). There are also
organelles composed of proteins: centriole, centrosome,
ribosomes (RNAs and proteins), cilia, flagella (undulipodia),
and proteasomes. Mitochondria and chloroplasts (plants),
organelles of the same size as bacteria, have the particularity
to contain DNA bacterial type (cf. Sects. 4.3.1 and 5.4.2).
They multiply independently of the host cell. The
amyloplasts of plants are specialized in synthesis and accumulation of starch. The presence of organelles and their
importance in eukaryotic cells depends on the types of
microorganisms and cellular activity.
Some eukaryotic microorganisms have a filamentous
vegetative apparatus (Fungi). According to the taxa, these
filaments are consisting of cells or a mass of multinucleated
cytoplasm (syncytium). It may also be alternating between a
single-cell generation and a filamentous generation (cf. Sect.
7.14.3).
3.2
Concept of Metabolism
The maintenance of cellular integrity, growth, and reproduction of living organisms requires the synthesis of cellular
material, which depends on nutrients entering the interior of
cells and subjected to a series of chemical changes. The sum
of these changes is responsible for the production of energy
(catabolism) and synthesis of biomolecules (anabolism); it is
the metabolism of the cell (Fig. 3.7). Metabolic reactions are
catalyzed by enzymes that, by combining with the biological
molecules, decrease the activation energy of reactions and
determine the reaction pathway to be used for the transformation of substances.
As sources of energy, the nutrient is oxidized, and the
energy produced during the oxidation is transferred as
energy-rich compounds, mostly in the form of ATP. These
reactions of oxidation or degradation are the cellular
catabolism:
1. In general, energy sources are organic compounds
(chemoorganotrophic microorganisms*).
The oxidation of organic compounds can be partial or
complete. When it is partial, the organic molecules of
small molecular weight are produced, more oxidized than
organic sources given as nutrients. The complete
Table 3.2 Characteristic organelles of eukaryotic cells
Organelles
Description
Function
Endoplasmic
reticulum (ER)
Flattened cavities (limited by smooth membranes or membranes
covered with ribosomes) and vesicles
Synthesis of glycoproteins, lipids, sterols; transport
of various substances
Ribosomes
80 S particles formed of two subunits of 40S and 60S
Synthesis of proteins, forming polysomes if arranged
in chains fixed to mRNA
Golgi apparatus
(GA)
Pile of flattened sacs formed from vesicles, derived from ER
Finishing synthesis (proteins), packaging, and secreting of
various cellular substances (lysosomes)
Lysosomes
Set of vesicles from the ER and GA
Containing hydrolytic enzymes, digestion of substrates
Vacuoles
Origin: ER and GA; large size in plant cells
Contractile vacuoles, digestive vacuoles; sequestration and
storage of substances; hydric balance of plant cells
Peroxisomes
Vesicles formed from the ER
Containing redox enzymes
Proteasome
Enzymatic complex
Digestion of endogenous proteins; regulation of enzyme
activity
Mitochondria
Rod about 2–3 μm long, double membrane with folded inner
membrane; containing DNA of prokaryotic type
Respiratory center of the cell, respiratory transporters,
and enzymes included in the inner membrane
Chloroplasts
Various lamellar structures (thylakoids); containing DNA
of prokaryotic type
Containing the photosynthetic pigments, photosynthesis
Centrioles
Formed by the association of microtubules
Formation of the centrosome; participate in the formation
of undulipodia
Centrosome
Formed from centrioles
Intracellular movements
Undulipodia
Cytoplasmic expansions containing microtubules inserted
on basal granules (kinetosomes)
Cellular movements
3 Structure and Functions of Microorganisms: Production and Use of Material and Energy
33