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
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Eukaryotic cells
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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
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Rod: bacillus (E.coli)
Coccus: round, spherical
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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
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Pleomorphic
 Within a population various
shapes (Corynebacteria)
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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)
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 Extracellular
polysaccharide allows cell
to attach
 Capsules prevent
phagocytosis
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Generate movement
Protein structure
 H-antigen (“Hauch”, used for typing)
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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
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Monotrichous: One only
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Lophotrichous: Multiple at
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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
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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
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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
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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
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Core sugar
 conserved
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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
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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
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Rich in mycolic acids
E.g. Mycobacterium spec
Hard to penetrate
Require heat for staining
ARCHAEA
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No peptidoglycan (murein)
Pseudomurein
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NAG
NAM
NAG
Penicillin
Lysozyme
NAG
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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)
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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
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 virulence factors
 antibiotic resistance
 toxic metal resistance
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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
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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
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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
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 Oxygenic
 Protein modification
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photosynthesis
Golgi
 Protein modification
Mitochondria
 ATP production
 Some eukaryotes do
Chloroplasts
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Peroxisomes
 Oxidation Reactions
not have mitochondria,
e.g. Giardia
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How did eukaryotes arise?
 DNA similar to archaea’s
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Mitochondrial, chloroplast
DNA
 Similar to bacterial DNA
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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.
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80S ribosomes (40S + 60S)
 Bigger than prokaryotic ribosome
 sediment differently
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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
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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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