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“Anatomy” and Function of
Prokaryotes
Dr. Hala Al- Daghistani
Bacteria have many sizes and several shapes. Most bacteria
range from 0.2 to 2.0 um in diameter and from 2 to 8 um in
length. They have a few basic shapes:
1. Spherical coccus (plural:cocci)
2. Rod-shaped bacillus (plural: bacilli)
3. Spiral.
- Cocci that remain in pairs after dividing are called Diplococci
- those that divide and remain attached in chain like patterns
are called Streptococci
- those that divide in two planes and remain in groups of four
are known as Tetrads. - Those that divide in three planes and
remain attached in cubelike groups of eight are called Sarcinae.
- Those that divide in multiple planes and form grapelike
dusters or broad sheets are called Staphylococci
Most bacilli appear as Single rods.
Diplobacilli appear in pairs after division , and
Streptobacilli occur in chains.
Some bacteria are rod and look so much like cocci
that they are called Coccobacilli
Cell Arrangement
Spiral bacteria have one or more twists.
Bacteria that look like curved rods are called Vibrios.
Others, called Spirilla, have a helical shape, and fairly
rigid bodies.
Another group of spirals are helical and flexible; they
are called Spirochetes.
Unlike the spirilla, which use external appendages
called flagella to move, spirochetes move by means of
axial filaments, which resemble flagella but are
contained within a flexible external sheath.
The shape of a bacterium is determined by
heredity. Genetically, most bacteria are
Monomorphic; that is, they maintain a single
shape.
Some bacteria, are genetically Pleomorphic.
Which means they can have many shapes, not
just one.
Spiral Bacteria
Prokaryote
“Anatomy”
Overview
Cell envelope: Collectively all the structures
outside from the plasma membrane.
Cytoplasmic Matrix and Structures
 Cytoplasmic proteins
 Ribosomes
 Nucleoid
 Inclusion Bodies
 Glycogen (G)
 Poly-β-hydroxybuterate (lipid)
 Cyanophycin (N) granules
 Carboxysomes (ribulose I.5 diphosphate carboxylase, CO2
fixation)
 Gas vacuoles (vesicles)
 Polyphosphate granules(volutin)
 Magnetosomes are inclusions of
iron oxide (Fe304)
 Sulfur granules
Inclusion Bodies
Gas Vacule = buoyancy
Magnetosomes = orientation
Ribosomes
• Subunits made of proteins and ribosomal ribonucleic acids (rRNA).
• 30S and 50S must bind together to form a complete and functional ribosome.
• The two subunits “sandwich” messenger RNA (mRNA).
• As it moves along the mRNA, the genetic code is “translated” into a
polypeptide by the directed polymerization of amino acids.
• Transfer RNAs (tRNA) shuttle the amino acids to the ribosome as needed.
• Hence, ribosomes are responsible for protein synthesis.
Plasma Membrane
• Membranes are lipid bilayers (hydrophilic outside and
hydrophobic inside)
• Functions:
–
–
–
–
Selective permeable barrier into (out of) cytoplasm.
Transport for nutrients, excretion, secretion
Sensing the environment & signaling a response
Metabolic processes (respiration; photosynthesis …)
Plasma
Membranes
Two Cell Wall Designs:
Gram-negative Cell Wall
Lipid A of LPS acts as endotoxin; O polysaccharides
are antigens for typing, e.g., E. coli O157:H7
Gram neg. bacteria are less sensitive to medications
because outer membrane acts as additional barrier.
LPS layer = outer layer of outer membrane
(protein rich gel-like fluid)
Cell Wall (Gram +)
Gram Stain
Differential staining to distinguish cell wall types.
(Christian Gram 1884)
Acid-fast Cell
Walls
• Genus Mycobacterium and Nocardia
• mycolic acid (waxy lipid) covers thin
peptidoglycan layer
• Do not stain well with Gram stain  use acidfast stain
Bacteria with No Cell Wall: Mycoplasmas
• Instead, have cell
membrane which
incorporates cholesterol
compounds (sterols),
similar to eukaryotic cells
• Cannot be detected by
typical light microscopy
pleomorphic Mycoplasmas
Cell Wall Biochemistry
What is peptidoglycan?
Structures External to the Cell Wall
Glycocalyx:
means sugar
coating; often polysaccharide or
polypeptide layer external to the
cell wall.
• Capsules: organized, consolidated,
well attached.
• Slime Layer: unorganized; loose;
removed easily.
• Function in attachment;
protection; virulence.
S-layer:
extremely well
organized layer of protein or
glycoprotein subunits that forms a
rigid mesh, next to cell wall.
Functions in
-adherence
-Protect the bacteria from enzyme
and change in Ph
-Contribute to virulence
(antiphagocytosis, anticomplements)
Structures External to the Cell Wall
Fimbriae:
Flagella:
• 1000’s of thin (~5 nm) & short
appendages of helical proteins.
• Mostly made of flagellin.
• Attachment to (specific) surfaces.
• Filament thick (20 nm) &
long (10-20 µm).
•Varied locations on cell:
Sex Pili:
• 1-10 slightly larger than fimbriae.
peritrichous
• Only in cells with a fertility plasmid
(F factor), called donors.
monotrichous
• Attaches to like cells without F
factor, called recipients.
• Facilitates genetic transfer between
cells; with recipient gaining the F
factor and possibly other genes.
amphitrichous
lophotrichous
Endospore Formation
Dormant, tough, non-reproductive structure  germination
 vegetative cells
Spore forming genera: Clostridium
Resistance to UV and  radiation, desiccation, lysozyme,
temperature, starvation, and chemical disinfectants
Relationship to disease
Sporulation: Endospore formation
Germination: Return to vegetative state
Sporulation
Depending on the species, the endospore might be located
terminally (at one end), subtermillally (near one end, or
celltrally inside the vegetative cell.
When the endospore matures, the vegetative cell wall
ruptures (lyses), killing the cell, and the endospore is freed.
Most of the water present in the forespore cytoplasm is
eliminated by the time sporulation is complete, and
endospores do not carry out metabolic reactions.
The highly dehydrated endospore core contains only DNA, small
amounts of RNA, ribosomes, enzymes, and a few important small
molecules. The latter include a large amount of an organic acid
called dipicolillic acid which is accompanied by a large number of
calcium ions.
Endospores can remain dormant for thousands of years. An
endospore returns to its vegetative state by a process called
Germination.
Sporulation in bacteria is not a means of reproduction. This
process does not increase the number of cells.