Samenvatting Unit 2 – Microbial cell structure and function
2.1 Cell morphology
Morphology = cell shape
Major morphology of prokaryotic cells
Major cell morphologies;
• Coccus; spherical or ovoid shape
• Rod/bacillus; cylindrical shape
• Spirillum; spiral shape
Cells with unusual shapes; spirochetes, appendage bacteria
and filamentous bacteria
Many variations on basic morphological types. For example,
diplococcus, streptococcus, staphylococcus. Coccobacillus (in
between coccus and rod), vibrio (rod that can bend).
Morphology and biology
The morphology of a given microbe is the result of the selective
forces that have shaped its evolution to maximize fitness for
competitive success in its habitat. (nutrient uptake etc.)
2.2 The small world
Size range for prokaryotes; 0,2 to 750 micrometers (very large prokyarotes are
uncommon)
Very large prokaryotes; Epulopiscium fishelsoni (600 micrometer) and
thiomargarita namibiensis (750 micrometer)
Size range for eukaryotes; 10 to >200 micrometers (very small eukaryotes are
uncommon)
Surface-to-volume rations, growth rates and evolution
S/V ratio; surface/volume; smaller cells have larger S/V ratio (more surface area
related to the volume).
What is the advantage of high S/V ratio?
• Support greater nutrient exchange per unit cell volume
• Tend to grow faster than larger cells, because of greater nutrient exchange
Lower limits of cell size
Cellular organisms <0,15 micrometer in diameter are unlikely; genome is to big. In all
the cells there has to be a genome.
2.3 The cytoplasmic membrane and wall
Cytoplasmic membrane; “gatekeeper” for the entrance and exit of dissolved
substances (selective permeability)
Cell wall; confers structural strength on the cell in order to keep it from bursting due
to osmotic pressure
, Cytoplasmic membrane
• 8-10 nm wide
• Thin structure that surround the cell
• Separates the cytoplasm from the environment
• Flexible ‘fluidic’ structure
The bacterial cytoplasmic membrane
Composition of membranes;
• General structure is phospholipid bilayer
• Can exist in different chemical forms as a result of
variation in the groups attached to the glycerol backbone.
• Fatty acids point inward; hydrophobic. Point outward;
hydrophilic.
o Hydrophobic component consists of fatty acids
o Hydrophilic component consists of glycerol
containing phosphate and one other functional
group
You need positive ions (Mg/Ca) to balance the negative phosphate ions. To help
stabilize membrane.
Membrane proteins;
• Integral membrane proteins
o Firmly embedded in the membrane
• Peripheral membrane proteins
o One portion anchored in the membrane
Archaeal membranes
This membrane is structurally similar to those of Bacteria and Eukarya, but chemistry
is different.
In bacteria and Eukaryote; Ester linkages between fatty
acids to glycerol
In Archaeal; ether linkages between hydrophobic side chain
(that is not fatty acid) to glycerol
Archaeal lack fatty acids they have isoprenes.
Cyotplasmic membrane of Archaeal have C20 side chains
(phytanyl) or C40 side chains (biphytanyl).
By the biphytanyl, the end and the begin are covalently linked to
form a lipid monolayer.
Cytoplasmic membrane function
Function;
• Protein anchor; holds transport proteins in place
• Energy conservation; generation of proton motive force
• Permeability barrier; prevents leakage and functions as a gateway for
transport of nutrient and wastes out and in. Polar and charged molecules must
be transported. Transport against concentration gradient
2.1 Cell morphology
Morphology = cell shape
Major morphology of prokaryotic cells
Major cell morphologies;
• Coccus; spherical or ovoid shape
• Rod/bacillus; cylindrical shape
• Spirillum; spiral shape
Cells with unusual shapes; spirochetes, appendage bacteria
and filamentous bacteria
Many variations on basic morphological types. For example,
diplococcus, streptococcus, staphylococcus. Coccobacillus (in
between coccus and rod), vibrio (rod that can bend).
Morphology and biology
The morphology of a given microbe is the result of the selective
forces that have shaped its evolution to maximize fitness for
competitive success in its habitat. (nutrient uptake etc.)
2.2 The small world
Size range for prokaryotes; 0,2 to 750 micrometers (very large prokyarotes are
uncommon)
Very large prokaryotes; Epulopiscium fishelsoni (600 micrometer) and
thiomargarita namibiensis (750 micrometer)
Size range for eukaryotes; 10 to >200 micrometers (very small eukaryotes are
uncommon)
Surface-to-volume rations, growth rates and evolution
S/V ratio; surface/volume; smaller cells have larger S/V ratio (more surface area
related to the volume).
What is the advantage of high S/V ratio?
• Support greater nutrient exchange per unit cell volume
• Tend to grow faster than larger cells, because of greater nutrient exchange
Lower limits of cell size
Cellular organisms <0,15 micrometer in diameter are unlikely; genome is to big. In all
the cells there has to be a genome.
2.3 The cytoplasmic membrane and wall
Cytoplasmic membrane; “gatekeeper” for the entrance and exit of dissolved
substances (selective permeability)
Cell wall; confers structural strength on the cell in order to keep it from bursting due
to osmotic pressure
, Cytoplasmic membrane
• 8-10 nm wide
• Thin structure that surround the cell
• Separates the cytoplasm from the environment
• Flexible ‘fluidic’ structure
The bacterial cytoplasmic membrane
Composition of membranes;
• General structure is phospholipid bilayer
• Can exist in different chemical forms as a result of
variation in the groups attached to the glycerol backbone.
• Fatty acids point inward; hydrophobic. Point outward;
hydrophilic.
o Hydrophobic component consists of fatty acids
o Hydrophilic component consists of glycerol
containing phosphate and one other functional
group
You need positive ions (Mg/Ca) to balance the negative phosphate ions. To help
stabilize membrane.
Membrane proteins;
• Integral membrane proteins
o Firmly embedded in the membrane
• Peripheral membrane proteins
o One portion anchored in the membrane
Archaeal membranes
This membrane is structurally similar to those of Bacteria and Eukarya, but chemistry
is different.
In bacteria and Eukaryote; Ester linkages between fatty
acids to glycerol
In Archaeal; ether linkages between hydrophobic side chain
(that is not fatty acid) to glycerol
Archaeal lack fatty acids they have isoprenes.
Cyotplasmic membrane of Archaeal have C20 side chains
(phytanyl) or C40 side chains (biphytanyl).
By the biphytanyl, the end and the begin are covalently linked to
form a lipid monolayer.
Cytoplasmic membrane function
Function;
• Protein anchor; holds transport proteins in place
• Energy conservation; generation of proton motive force
• Permeability barrier; prevents leakage and functions as a gateway for
transport of nutrient and wastes out and in. Polar and charged molecules must
be transported. Transport against concentration gradient
