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Anatomy and Physiology of
Prokaryotic Cells
Microbiology
Mrs. Hieneman
Bacterial Shape and Arrangement
Streptococcus chain
Sarcinae cube
Staphylococcus aureus cluster
Spiral-shaped bacterial cell
Prokaryotic Cell Structure
Cytoplasmic Membrane
• Surrounds cytoplasm and defines
boundaries of cell
• Acts as barrier, but also functions as an
effective and highly discriminating conduit
between cell and surroundings
• Made up of phospholipid bilayer
Figure 4.14c
Phospholipid
Figure 4.14b
Movement of Molecules through
Cytoplasmic Membrane
•
1.
2.
3.
4.
Several ways for molecules to move
through membrane
Simple Diffusion
Osmosis
Facilitated Diffusion
Active Transport
Simple Diffusion
• Does not require expenditure of energy
• Process by which some molecules move
freely into and out of the cell
• Small molecules such as carbon dioxide and
oxygen
Figure 4.18: The principle of osmosis - Overview.
Glass tube
Rubber
stopper
Rubber
band
Sucrose
molecule
Cellophane
sack
Water
molecule
(a) At beginning of osmotic
pressure experiment
Cytoplasm
Solute
(b) At equilibrium
Plasma membrane
Cell wall
Water
(c) Isotonic solution —
no net movement of water
Microbiology: An Introduction, 9e
by Tortora, Funke, Case
(d) Hypotonic solution —
water moves into the cell and
may cause the cell to burst if
the wall is weak or damaged
(osmotic lysis)
(e) Hypertonic solution —
water moves out of the cell,
causing its cytoplasm to shrink
(plasmolysis)
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Transport Proteins
• Transport proteins (or transporters)
responsible for:
• Facilitated Diffusion
• Active Transport
Figure 4.17: Facilitated diffusion.
Transported
substance
Transporter
protein
Outside
Plasma
membrane
Inside
Glucose
Microbiology: An Introduction, 9e
by Tortora, Funke, Case
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Cell Wall
• Composed of peptidoglycan
• Comprised of alternating NAG and NAM
molecules
• Attached to each NAM is four amino acid
peptide: tetrapeptide
Categories of Bacteria
• Two Major Categories:
• Difference due to difference in chemical
structures of their cell walls
– Gram positive: stains purple
– Gram negative: stains red
Gram + Cell Wall
• Thick Layer of Peptidoglycan
• Contains techoic acid: chains of ribitolphosphate or glycerol-phosphate to which
sugars or alanine attached
• Techoic Acid sticks out above the
peptidoglycan layer
Gram – Cell Wall
• More complex than Gram + cell wall
• Thin layer of peptidoglycan
– Sandwiched between the cytoplasmic
membrane and outer membrane
• Outside of peptidoglycan is outer membrane
Figure 4.13c
Outer Membrane
• Unlike any other membrane in nature
• A lipid bilayer with the outside layer made
of lipopolysaccharides instead of
phospholipids
• Also called LPS
• Contains Porins
Periplasm
- Region between cytoplasmic membrane and
the outer membrane
- Gel-like fluid
• Filled with secreted proteins and enzymes
External Structures
•
•
•
•
Glycocallyx
Flagella
Axial Filaments
Fimbrae and Pili
Glycocallyx
• Gel-like structure
– Functions in protection and attachment
– Two types- capsule and slime layer
– Involved in attachment, enabling bacteria to
stick to teeth, rocks
– Enables bacteria to brow as biofilm
Capsule in Acinetobacter species by gram negative staining
Filamentous Protein Appendages
• Anchored in membrane and protrude from
surface
• Flagella: long structure responsible for
motility
• Fimbrae and Pili: shorter, responsible for
attachment
Four types of bacteria with flagella
• Montrichious- one flagella
• Amphitrichous- flagella at both ends
• Lophitrichous- many flagella at the end of
the cell
• Peritrichous- flagella all over entire cell
Figure 4.7 - Overview
Axial Filament
• Present in Spirochetes
• Attach at end of cell, spiral around,
underneath an outer sheath
• Move like a corkscrew
Figure 4.10 - Overview
Fimbrae and Pili
• Shorter and surround the cell
• Similar structural theme to filament of
flagella
• Fimbrae- enable cell to adhere to surfaces,
including other cells
• Pili- join bacterial cells in preparation for
the transfer of DNA from one cell to
another
Internal Structures of Prokaryotic
Cells
Cytoplasm
• Substance of cell inside the cytoplasmic
membrane
• About 80% water
• Thick, aqueous, semitransparent, elastic
Chromosome
• Found within a central location known as
nucleoid
• Single, circular, double stranded
• Consists of all DNA required by cell
Plasmids
• Some bacteria contain plasmids- small
circular double-stranded DNA
• Typically cell does not require genetic
information carried on plasmid
• However, it may be advantageous
Ribosomes
• Site of protein synthesis
• Relative size and density of ribosomes and
their subunits expressed as distinct unit (S)
• Two units of prokaryotic ribosomes: 50S +
30S= 70S
• Eukaryotic ribosomes: 80S
Figure 4.19: The prokaryotic ribosome.
50S
30S
(a) Small subunit
Microbiology: An Introduction, 9e
by Tortora, Funke, Case
50S
(b) Large subunit
30S
(c) Complete 70S
ribosome
Copyright © 2007 Pearson Education, Inc.,
publishing as Benjamin Cummings.
Inclusions
• Store excess nutrients
• Examples: Polysaccharide granulesglycogen and starch
• Lipid inclusions
• Metachromatic granules- inorganic
phosphate that can be used to synthesize
ATP
Endospores
• Occurs in members of genera Bacillus and
Clostridium
• Dormant cell produced by a process called
Sporulation
• Germination- when they exit the dormant
state and then become a vegetative cell
• Several species of endospore formers can
cause disease