Bacteria and archaea are usually ~ ___ in diameter
1 μm
Eukaryotic cells are usually 10-100 x
larger
Be able to identify prokaryotic cell arrangements
(I.e. streptococci)
Prokaryotic Glycocalyces (sing. glycocalyx)
● The glycocalyx surrounds the cell wall and prevents organisms from drying out
● Secreted by cell onto its surface
Capsule: tightly bound to cell wall
■ Protect cell from immune detection
■ Includes polypeptides and polysaccharides
Exopolysaccharide (NOT slime layer): loosely excreted around cell membrane
■ Form biofilms to help bacteria stick to surfaces
■ Biofilm communities can include diverse species and genera of bacteria
● Adhesins also promote attachment of bacteria to surfaces, but are not considered part of the glycocalyx
Prokaryotic Flagellum
i. Structure:
1) Basal body: integral to the cell wall and membrane
2) Hook: bent connector piece
3) Filament: hollow shaft made of flagellin, synthesized from distal tip
ii. Arrangement Polar
■ Bundled or singular
○ Peritrichous
○ Endoflagella/axial flagella
(Slide 19)
iii. Motility
○ Counterclockwise: run toward/away from stimulant (taxis)
○ Clockwise: tumble in random motion, sampling environment
Function: Motility, chemotaxis.
Prokaryotic Fimbrae
● Facilitates twitching motility and adherence to surfaces
○ Pulls itself along by polymerizing, sticking into a surface, and drawing itself across the surface by depolymerizing
● Helpful especially in mucousy environments
● Contain adhesin
● Shorter, more bristly than flagella
● First step of biofilm formation–stick into surface and allow for persistent infection
Swimming, swarming, twitching
Swimming: Individual cells, liquid, powered by flagella. Counterclockwise movement of flagella
Tumbling: Clockwise
Swarming: Coordinated group movement across surfaces, flagella-based, associated with biofilm/virulence.
Twitching: Surface movement using type IV pili (extend/retract), jerky motion. “arm over arm” movement of fimbria.
Define chemotaxis
Movement of a motile cell or organism in a direction corresponding to a gradient of
increasing or decreasing concentration of a particular substance.
Phototaxis
movement with regard to light
Pilus
● NOT bacterial sex
● One mechanism for horizontal gene transfer via conjugation pilus
● Made of protein called pilin – hollow tube through which genetic material can pass one bacterium to
another
● Until recently, thought to be exclusive to Gram (-) bacteria
○ Turns our Gram + have pili, but different proteins for conjugation
● Occurs during cell replication
Define exopolysaccharide
A polysaccharide secreted by an organism into the environment
Define adhesin
Cell-surface components or appendages of bacteria that facilitate bacterial adhesion or
adherence to other cells or to inanimate surfaces
Define Signal Transduction
A mechanism that converts a mechanical/chemical stimulus to a cell into a specific cellular response
Prokaryotic Cell: Cell Membrane
-Phospholipid bilayer
-Fluid mosaic model.
-Cell membrane interfaces with environment and “senses” surroundings
-Semi-permeable
Prokaryotic Cell Envelope
The prokaryotic cell envelope is the protective outer covering of a prokaryotic cell, primarily in bacteria and archaea, that includes the cell membrane, the cell wall (if present), and an outer membrane like the glycocalyx (if present).
Cytoplasmic membrane in prokaryotic and eukaryotic cells is composed of phospholipid bilayer
● An assortment of lipids, proteins, carbohydrates, and complexes of
these macromolecules embedded in or attached to the membrane –
fluid mosaic model
● Signal transduction is the process by which a stimulant starts a
chain of events that leads to some product/process occurring within
the cell
○ Can happen via the cell membrane components or within the cell
● Cell membrane interfaces with environment and “senses”
surroundings
● Cell membrane is semi-permeable – small, hydrophobic molecules
can pass through, while larger/hydrophilic molecules require active transport.
○ Helps maintain a concentration gradient
Functions: permeability barrier, transport, energy generation (proton motive force), signal transduction.
Prokaryotic Cell: Cell Wall
Peptidoglycan: repeating subunits of N-acetylglucosamine
(NAG) and N-acetylmuramic acid (NAM) bound by -1,4 linkageꞵ
and stabilized by short peptide crossbridges
Why are cell walls a good antibiotic target?
Bacterial cell walls are ideal antibiotic targets because they are essential for bacterial survival, absent in human cells, and unique to bacteria, making it possible to develop drugs that specifically kill bacteria without harming human cells. By interfering with cell wall synthesis or integrity, antibiotics can weaken or destroy the cell, causing the bacterium to lyse (burst) due to osmotic pressure.
Compare and contrast the Gram-positive and Gram-negative cell wall. Discuss the Gram staining process and how it relates to the properties of the cell.
Gram positive bacteria: bacteria with a thick peptidoglycan cell wall and one membrane inside the wall
Gram negative bacteria: bacteria with a thin peptidoglycan cell wall with two membranes, one on either
side of the wall. Gram negative outer membrane includes lipopolysaccharide (LPS), formed from lipid A (a toxin to human cells).
The Gram stain differentiates bacteria based on the chemical and physical properties of their cell walls, which directly affects how they retain stains.
1. Crystal Violet (Primary Stain):
All bacteria are stained purple by the primary stain, crystal violet.
2. Gram’s Iodine (Mordant):
Iodine is added, forming large crystal violet-iodine complexes within the cells, which strengthen the stain’s adherence to the cell wall.
3. Alcohol (Decolorizer):
This is the critical step that differentiates the two types.
Gram-Positive: The alcohol dehydrates and shrinks the thick peptidoglycan layer, trapping the crystal violet-iodine complexes inside, so the cells remain purple.
Gram-Negative: The alcohol disrupts the outer membrane and thins the peptidoglycan layer, causing the crystal violet-iodine complexes to be washed out of the cells, leaving them colorless.
4. Safranin (Counterstain):
A pink or red dye, safranin, is added.
Gram-Positive: The purple color from the crystal violet remains dominant.
Gram-Negative: The decolorized cells now absorb the safranin, turning pink or red and becoming visible under a microscope.
Lipopolysaccharide (LPS)
Consists of three parts:
○ lipid A
○ core polysaccharide
○ O side chain (O
antigen)
● Contributes to negative charge on cell surface
● Helps stabilize outer membrane structure
● May contribute to attachment to surfaces and biofilm formation
● Creates a permeability barrier
● Protection from host defenses (O antigen)
● Can act as an endotoxin (lipid A)
● Sneaky little bugger
Acid-fast bacteria
○ Gram positive bacteria that have a special waxy layer
composed of mycolic acid
○ Gives the name to the most famous genera of acid-
fast bacteria: Mycobacteria
■ Causative agents of leprosy and TB
Gram staining: technique developed by Hans Christian Gram to differentially dye bacteria with thick vs. thin cell walls
- Stain fixed cells with crystal violet (primary stain)
- Add Gram’s iodine (mordant)
- Wash with ethanol (decolorize)
- Stain with safranin (counterstain)
You’ll get more of this in lab/in the microscopy lecture!
Prokaryotic Cell: Cytoplasm
● The yummy protein-sugar interior of the cell
● Less crowded that in a eukaryotic cell
● Home of ribosomes, nucleoid, and pretty much every other internal process the prokaryotic cell does
○ Metabolism
○ DNA replication, transcription, and translation
● No membrane-bound organelles
● Inclusions - lipid droplets, phase separation
● Some have endospores - dormant cell structures formed in times of
environmental stress, “rainy day” plan
Prokaryotic Cell: Endospores
● Most famous producers of endospores: Bacillus and Clostridium
genera
● Can survive for 1000s of years
● Non-reproductive – only job is to sit and wait in dormancy
● Virulence factor – when the going gets tough, the tough get going
● Open research question – how do spores know to reactivate as
vegetative cells?
Endospore Stain Protocol, ASM.
Sporulation
Be able to identify the process
Nucleoid
Region of cell where DNA is concentrated
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Chapter 1: Origins of Microbiology14
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Chapter 2: Chemistry of Microbiology17
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Chapter 3: Cell Structure and Function47
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Chapter 4: Viruses, Viroids, Prions27
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Test One Vocab Terms15
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Chapter 5: Microscopy14
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Chapter 6: Taxonomy11
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Chapter 7: Microbial Metabolism13
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Chapter 8: Microbial Growth12
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Chapter 9: Microbial Control4
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Test Two Vocab Terms53
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Chapter 10: Microbial Genetics25
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Chapter 11: DNA Technology1
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Chapter 12: Pathogenesis12
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Test Three Vocab Terms0
