Lec2 Prokaryotic and Eukaryotic cells
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Transcript Lec2 Prokaryotic and Eukaryotic cells
Lecture 2: Functional Anatomy of Prokaryotic and Eukaryotic cells
Edith Porter, M.D.
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Major characteristics of prokaryotic and eukaryotic cells
Prokaryotic cells
Eukaryotic cells
Size, shape arrangement
Structures external to cell wall
Cell wall
Structures internal to cell wall
Flagella and cilia
Cell wall and glycokalyx
Plasma membrane
Ribosomes and organelles
Evolution of eukaryotes
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One circular
chromosome, not in
a membrane
No histones
No organelles
Peptidoglycan cell
walls if Bacteria
Pseudomurein cell
walls if Archaea
Binary fission
Paired chromosomes,
in nuclear membrane
Histones
Organelles
Polysaccharide cell walls
Mitotic spindle
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Typically fixed shape due to cell wall
Peptidoglycan (murein) in bacteria
Pseudomurein in archaea
Rod: bacillus (E.coli)
Coccus: round, spherical
Diplococci (N. meningitidis)
Streptococci (S. pyogenes)
Tetrades (Micrococci)
Sarcinae
Staphylococci (Staphylococcus epidermidis)
Spiral
Fixed: spirilla
Flexible: spirochetes (Treponema pallidum)
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Unusual
Star-shaped
Squares
Triangular
Pleomorphic
Within a population various
shapes (Corynebacteria)
No fixed shape
Cellwall-less:
Mycoplasma/Ureaplasma
Shape is influenced by
environmental conditions, age of
culture, antibiotic pretreatment!
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Outer most layer
Outside cell wall
Usually sticky
Composed of mostly
of carbohydrates,
sometimes of protein
Capsule: neatly
organized
Slime layer: unorganized
and loose
Biofilm or
extracellular
polymeric substance
(EPS)
Extracellular
polysaccharide allows cell
to attach
Capsules prevent
phagocytosis
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Generate movement
Protein structure
H-antigen (“Hauch”, used for typing)
Consists of 3 parts:
Filament: flagellin subunits (H-antigen),
helical arranged
Hook
Basal body: anchors into the cell wall via
rings, here movement is generated
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In Gram-negative bacteria
In Gram-positive bacteria
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Peritrichous: Many around
Monotrichous: One only
Lophotrichous: Multiple at
Amphitrichous: At both ends
one end
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Also called endoflagella
In spirochetes (e.g., Treponema, Borrelia)
Anchored at one end of a cell and beneath an outer sheet
Rotation causes cell to move
Suited for movement in viscous surrounding
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Chemotaxis
Directed movement
In response to a chemical
Through a specific chemoreceptor on the cell
Movement to a chemical: chemical is a
chemoattractant (e.g. sugar, amino acid)
Movement away from chemical: chemical is a
chemorepellent (toxic substance)
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Cell appendages in mostly gram-negative bacteria
Made out of protein subunits (pilin)
Thinner than flagella
Fimbria
a few – hundreds
Main function is attachment
Pili
typically 1 or 2 only and longer
DNA transfer: Specialized sex pili transfer plasmids during
bacterial conjugation
Twitching motility and gliding motility
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Figure 4.11
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Peptidoglycan is major
component
Cross linkage of peptides + sugars
Sugars: multiple layers of
alternating N-acetylmuramic acid
(NAM) and N-acetylglucosamine
(NAG)
Peptides: tetrapeptide crosslink
between NAM from different
layers, D- and L- amino acids
NAG
NAG
NAM
NAM
NAG
NAG
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Gram-positive
Many layers of
peptidoglycan
Additional components
▪ Teichoic acid, lipoteichoic
acids
Periplasm in the space
between cell membrane
and peptidoglycan
Gram-negative
One or few layers of
peptidoglycan
Additional outer
membrane
▪ Mainly composed of
lipopolysaccharide
Lipoproteins connect
peptidoglycan with outer
membrane
Periplasm between cell
membrane and
peptidoglycan and
between peptidoglycan
and outer membrane
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Lipid A
the culprit for fever (endotoxin)
highly conserved
Core sugar
conserved
Sugar chain of varying length (O-antigen, “ohne
Hauch”, used for typing)
Lipid A
Core
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Gram stain:
1 min Crystal violet
1 min Iodine
destain in alcohol
1 min safranin
2 types of staining:
Gram+: thick PG
Gram-: thin PG, om
gram+
gram-
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None
Table 4.1
ACID FAST CELL WALLS
Rich in mycolic acids
E.g. Mycobacterium spec
Hard to penetrate
Require heat for staining
ARCHAEA
No peptidoglycan (murein)
Pseudomurein
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NAG
NAM
NAG
Penicillin
Lysozyme
NAG
NAM
NAG
Penicillin: inhibits transpeptidases
Lysozyme: breaks glycosidic bond between NAM and NAG
Autolysins: self destruction of peptidoglycan, important for
cell divisions
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Also called inner membrane
Double phospholipid layer with proteins (often
glycoproteins)
Lipids differ from eukaryotic cell membranes
No sterols (exception: Mycoplasma steal sterols from
host)
Protection towards outside
Containment of cytoplasmic material
Selective uptake of molecules
Site of energy production in many species
Target of some antibiotics (e.g. polymyxin B)
and disinfectants (e.g. alcohols)
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Figure 4.14
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~80% water
Contains primarily
proteins (enzymes),
carbohydrates, lipids,
inorgainc ions, many
low molecular weight
compounds
Thick, aqueous,
semitransparent, and
elastic
(from Slonczewski 2009)
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Bacterial chromosome
Contains the essential
genetic information
Circular double-stranded
DNA Stabilized by
histone-like proteins (not
by histones)
No nuclear envelope!!
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Small circular double-stranded
DNA that can multiply
independently
Not essential under normal
physiological conditions
Contain additional genes often
involved in pathogenesis
virulence factors
antibiotic resistance
toxic metal resistance
http://universe-review.ca/I10-71-plasmid.jpg
Copy number varies (a few –
hundreds)
Can be exploited for recombinant
protein production
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70S ribosomes (30S + 50S subunit)
S = Svedberg unit (sedimentation rate upon centrifugation)
smaller than eukaryotic ribosome
sediment differently
Consist of proteins and ribosomal RNA
Site of protein synthesis
Contain 16S rRNA on 30S subunit
Important for Classification and Identification!
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Storage granules (lipids, carbohydrates,
phosphate etc)
Caroxysomes (important for carbon dioxide
fixation in photosynthesis)
Gas vesicles for bouyancy
Magnetosomes
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Spore
Germination
Sporulation
Vegetative Form
Terminal
Subterminal
Central
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Sporulation is a complex
process
Triggered under unfavorable
conditions
Very low water content
Spore is multilayered
Resistance through spore coat
(protein layer)
Can survive thousands of years
Germination is triggered under
favorable conditions
Clostridium spec., Bacillus spec.
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1.
Which of the following is not a distinguishing
characteristic of prokaryotic cells?
a.
b.
c.
d.
e.
They have a single, circular chromosome
They lack membrane-enclosed organelles
They have a cell wall containing peptidoglycan
Their DNA is not associated with histones
They lack a plasma membrane.
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2. Which of the following is not true of fimbriae?
a. They are composed of protein
b. They may be used for attachment.
c. They are composed of carbohydrates.
d. They may be found on gram-negative cells.
e. All of above is true.
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Figure 4.22a
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Typically larger (10 – 100 mm)
Cell membrane contains sterols
Nucleus
Membrane-enclosed chromosomes
Linear DNA
Nucleolus: site of rRNA synthesis
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Endoplasmatic
reticulum
Oxygenic
Protein modification
photosynthesis
Golgi
Protein modification
Mitochondria
ATP production
Some eukaryotes do
Chloroplasts
Peroxisomes
Oxidation Reactions
not have mitochondria,
e.g. Giardia
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How did eukaryotes arise?
DNA similar to archaea’s
Mitochondrial, chloroplast
DNA
Similar to bacterial DNA
Endosymbiont theory:
Mitochondria WERE bacteria
Chloroplasts WERE cyanobacteria
Infected or eaten by other species
Ended up living together inside
▪ Endo-sym-biosis
Microbiology: An Evolving Science
© 2009 W. W. Norton & Company, Inc.
80S ribosomes (40S + 60S)
Bigger than prokaryotic ribosome
sediment differently
Consist of proteins and ribosomal RNA
Site of protein synthesis
Contain 18S rRNA subunit
Important for identification
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Flagella
9+2 microtubili
Wave-type movement
Cytoskeleton
Cell Wall
No peptidoglycan!
Instead cellulose (algae) and chitin (fungi)
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Prokaryotes are cells without a nucleus.
Prokaryotes always have a cell membrane, a
nucleoid and 70S ribosomes with 16S rRNA.
Eukaryotes always have a cell membrane, a
nucleus, 80S ribosomes with 18S rRNA, and
membrane-encoded organelles
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