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Prokaryotic Cell Structure
Chapter 3
Prokaryotes vs Eukaryotes
Prokaryotes
Eukaryotes
DNA
Organelles
Size &
Organization
Kingdoms
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Where do viruses fit in?
„ Acellular microorganisms
Cannot reproduce outside of host cell
„ No metabolism outside of host cell
„ RNA or DNA – never both
„
„ Debate: living or non-living?
Prokaryotic Cell Shapes
„ 3 Main Shapes
Rods
„ Cocci
„ Spirals
„
„
„
Spirochetes Æ flexible
Spirillum Æ stiff
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Other Prokaryotic Shapes
„ Coccobacillus
„ Vibrio
„ Pleomorphic
Typical Prokaryotic Cell
Fimbriae
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Prokaryotic Cell Structures
„ External structures
Glycocalyx
„ Flagella
„ Pili / fimbriae
„ Cell wall
„ Gram-positive and Gram-negative
„ Cell membrane
„ Internal structures
„ DNA, RNA, proteins
„ Ribosomes
„ Endospores
„
Glycocalyx
„ Made of polysaccharides, polypeptides, or
both
„ Two types
Capsule
„ Slime Layer
„
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Capsule
„ Organized
„ Firmly attached
„ Functions:
Protection
„ Virulence factor
„
Capsule
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Slime layer
„ Loosely attached
„ Water soluble
„ Functions:
Protection
„ Attachment
„
„
Biofilms
Flagella
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Flagella
„ Filament, hook, and
basal body
„ Filament made of
flagellin
„ Filament can rotate
360º
Flagella arrangements
Monotrichous
Lophotrichous
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Flagella arrangements
Amphitrichous
Peritrichous
Function of Flagella
„ Movement
„
Rotate counterclockwise or clockwise
„ Runs
„ Tumbles
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Fimbriae
Pili
„ Hollow tubules
Regular pili
„ Conjugation pili
„
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Fimbriae and Pili
Bacterial Cell Walls
„ Composed of peptidoglycan
„
Polymer of N-acetylmuramic acid (NAM) and
N-acetyl glucosamine (NAG)
„ Attached by tetrapeptide crossbridges
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Types of bacterial cell walls
„ Gram-positive
„
Thick layer of peptidoglycan
„ Gram-negative
„
Thin layer of peptidoglycan plus an outer
membrane
Gram-positive cell walls
„ Gram-stain purple
„ Thick layer of
peptidoglycan
„ Teichoic acids and
lipoteichoic acids
present
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Gram Stain (Gram-positive)
Gram+ Genera Examples
„ Bacillus
„ Clostridium
„ Streptococcus
„ Staphylococcus
„ Listeria
„ Corynebacterium
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Acid-fast cells
„ Gram-positive cells
„ Extra stuff in cell wall
Mycolic acid
„ Resistant
„
„ Special staining
procedure – Acid fast
stain
Acid Fast Stain
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Acid-Fast Genera Examples
„ Mycobacterium
„ Nocardia
Gram-negative cell walls
„ Gram-stain pink
„ Thin layer of
peptidoglycan
„ Outer membrane
„ Periplasmic space
between inner &
outer membranes
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Gram Stain (Gram-negative)
Gram- Genera Examples
„ Escherichia
„ Salmonella
„ Shigella
„ Bordetella
„ Neisseria
„ Pseudomonas
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Gram-negative outer membrane
„ Also called cell envelope
„ Phospholipid bilayer
Lipopolysaccharides
„ Porins
„ Other proteins
„
Lipopolysaccharide (LPS)
„ Lipid + sugar
„ Also known as endotoxin
„ Lipid portion known as lipid A
„ Released from dead/damaged cells
„ May trigger fever, vasodilation,
inflammation, shock, and
disseminated intravascular
coagulation (DIC)
„ Can be released when antimicrobial
drugs kill bacteria
Sugar
Lipid A
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Periplasmic space
„ Between outer membrane and cell membrane
„
Contains peptidoglycan and periplasm
Periplasmic space
Bacteria without Cell Walls
„ Mycoplasma
„
Sterols in cell membrane
„ Chlamydia
Cell membrane + outer membrane
„ No peptidoglycan
„
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Prokaryotic Cytoplasmic Membrane
Functions of Cytoplasmic Membrane
„ Selectively permeable
„ Energy production
„
Proton motive force (PMF)
„ Photosynthesis
„
photosynthetic prokaryotes
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Internal Prokaryotic Structures
„ Cytosol
„ Inclusions
„ Ribosomes
„ Cytoskeleton
Prokaryotic Ribosomes
50S
70S
30S
S = Svedberg unit
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Endospores
„ Formed by Bacillus and Clostridium
„ Defensive strategy
Metabolically inactive
„ Germinate in favorable conditions
„
Endospore Formation
Mother cell
(keratin)
Spore core
(Dipicolinic acid
+ calcium)
(peptidoglycan)
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Spore structure
Outer Spore Coat
(Exosporium)
Spore Coat
Outer membrane
Cortex
Inner membrane
Spore Core
Types of Endospores
Terminal
Central
Subterminal
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Endospore Stain
Cell Division in Prokaryotes
„ Asexual
„ Binary fission is
most common
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Cell Division
„ Snapping division
„
Palisades and Vhapes
Cell Division
„ Budding
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Cell Arrangements
„ Result from
Plane of cell division
„ Extent of separation of daughter cells
„
„ Cocci Æ multiple planes
„ Bacilli Æ single plane
Coccus
Bacillus
Arrangements of Cocci
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Arrangements of Bacilli
What about Eukaryotes?
„ Some have flagella
Different structure than prokaryotes
„ Similar to eukaryotic cilia
„
„ Some have a glycocalyx
„
Less organized than prokaryotes
„ Some have cell walls
Plants, fungi, algae
„ Polysaccharides such as cellulose & chitin
„
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What about Eukaryotes?
„ All have a cell membrane
Phospholipid bilayer
„ Capable of endo- and exocytosis
„
„ All have ribosomes
„
80S ribosomes – 40S + 60S
Eukaryotic organelles
„ Membrane-bound organelles
Nucleus
„ Endoplasmic reticulum
„ Golgi apparatus
„ Lysosome
„ Mitochondria
„ Chloroplast
„
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Mitochondria & Chloroplasts
„ Surrounded by phospholipid bilayer
„ Contain a circular molecule of DNA
„ Contain 70S ribosomes
Cell Division in Eukaryotes
„ Mitosis
„ Meiosis
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Last but not least . . . Nomenclature!
„ Genus + species
„ Escherichia coli
„ E. coli
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