Download Lecture 03 – Prokaryotes 3 Domains Comparison (Pro vs. Eu)

Lecture 03 – Prokaryotes
Topics
– Characteristics (comparison)
– External Structures
– Cell Envelope
– Internal Structures
– Cell Shapes, Arrangement, and Sizes
– Classification
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3 Domains
•
The Domains:
– Archae
– Bacteria
– Eukaryotes
•
Characteristics include
–
–
–
–
Ribosomes
Membrane lipids
tRNA
antibiotics
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Comparison (Pro vs. Eu)
• No nuclear
membrane
• 0.2-2.0 um
• No membrane
bound organelles
• Simple flagella, 2
proteins
• Glycocalyx: capsule
or slime layers
• True nucleus
• 10-100 um
• Organelles
(lysosomes, Golgi,
ER, etc.)
• Complex flagella,
microtubules
• Possibly in those
w/o cell wall
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Comparison (cont.)
• Complex cell wall
(incl. peptidoglycan)
• Plasma membrane:
few if any sterols, no
carbos
• No cytoskeleton or
cyto streaming
• Simple cell wall, if
present
• Plasma membrane:
sterols and carbos
• Cytoskeleton, cyto
streaming
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Comparison (cont...)
• Small Ribosomes70S
• DNA: Single,
circular, no histones
• Binary fission
• Recombination: no
meiosis, fragment
transfer only
• Large ribosomes 80S + 70S in
organelles
• DNA: Multiple,
linear, w/ histones
• Mitosis
• Recombination:
meiosis
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Bacteria
•
•
•
•
•
•
No membrane bounded organelles
Peptidoglycans
Antibiotic sensitivity
Binary fission
No Histones
70S ribosome
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Typical prokaryotic cell
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Figure 3.2
Approximate sizes of cells
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Figure 3.4
External Structures
• Flagella
• Pili and fimbriae
• Glycocalyx
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Flagella
• Composed of protein subunits
• Motility (chemotaxis)
• Varied arrangement (ex. Monotrichous,
lophotrichous, amphitrichous)
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Flagella Arrangements
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Three main parts of the flagella include the basal body, hook, and
filament.
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Details of the basal body in gram negative cell
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Different arrangements of flagella exist for different species.
Some flagella arrangements.
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Pili and fimbriae
• Attachment
• Mating (Conjugation)
• Fimbriae: Fimbriae are smaller than flagella, and
are important for attachment.
• Pili: Pili enable conjugation
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The Pilus (pili)
• Tubules composed of pilin
• Longer than fimbriae but
shorter than flagella
• Typically one or two per cell
• (conjugation)
Three bacteria in the process of conjugating
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Fimbriae - so what are they?
• Sticky, bristle like projections
• Used by bacteria to adhere to
one another, to hosts, and to
substances in environment
• Shorter than flagella
• Serve an important function
in biofilms
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Glycocalyx
• Capsule
– Protects bacteria from immune cells
(sticky)
• Slime layer
– Enable attachment and aggregation of
bacterial cells
– loosely bound to the cell, H2O soluble
– associated with the formation of biofilms (e.g.. on
teeth)
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Glycocalyces
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Figure 3.5
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The capsule is tightly
bound to the cell, and is
associated with
pathogenic bacteria.
Capsule = halo
Center = bacterial cell
Encapsulated bacteria
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Cell envelope
• Cell wall
– Gram-positive
– Gram-negative
• Cytoplasmic membrane
• Non cell wall
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Cell wall
• Gram positive cell wall (+ Purple)
– Thick peptidoglycan (PG) layer
– Acidic polysaccharides
– Teichoic acid and lipoteichoic acid
• Gram-negative cell wall (- Pink)
–
–
–
–
Thin PG layer
Outer membrane
Lipid polysaccharide
Porins
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Structures associated with gram + and gram - cell walls.
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Structure comparison gram-positive and gram-negative cell walls.
Cytoplasmic membrane
• Site of :
– Embedded proteins
– Energy generation
– Transport
• L-forms lose the ability to synthesize cell
walls (see next slide…)
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L-form = No cell wall
• No PG layer
• Cell membrane
contains sterols for
stability
• Example: Mycoplasma
sp.
Image from: http://www.health-spy.com
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Internal Structures
•
•
•
•
•
Cytoplasm
Genetic structures
Storage bodies (inclusion bodies)
Actin (protein fiber cytoskeleton)
Endospore (survival, triple-walled)
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Cytoplasm
• Gelatinous solution containing water,
nutrients, proteins, and genetic material.
• Site for cell metabolism
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Genetic structures
• Deoxyribonucleic
acid (DNA) - circular
• Ribonucleic acid
(RNA)
• Ribosomes –
(70S = 50S+30S)
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Images from: (dna) http://www.turbosquid.com (ribosome): http://pimm.wordpress.com
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Ribosomes
Ribosome:
•a combination of
RNA and protein
•involved in protein
synthesis.
•2 subunits
Model of a prokaryotic
ribosome.
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Cell shapes
•
•
•
•
•
•
Coccus
Rod or bacillus
Curved or spiral
pleomorphism (multi-shape)
Cell arrangements
Cell size
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Cellular shapes and arrangements are specific characteristics you
can use to help identify bacteria.
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Relative size of bacterial cell compared to other cells,
including viruses.
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Classification
• Phenotypic methods (biochemical +
staining)
• Molecular methods (sequencing)
• Taxonomic scheme
• Unique groups
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Methods of classification enable bacteria to be grouped into
different divisions and classes.
Bergey’s Manual
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Unique groups of bacteria
• Intracellular parasites (ex. Rickettsia sp.)
• Photosynthetic (oxygenic) bacteria
(Cyanobacteria)
• Photosynthetic (non-oxygenic) bacteria
(green and purple sulfur bacteria)
• Gliding and fruiting bacteria
• Archaea bacteria
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Archaea bacteria
• Associated with extreme environments
• Contain unique cell walls
• Contain unique internal structures
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Archae
• Lack peptidoglycans
• Have glycocalyx, flagella, fibriae, hami
• Inhabit extreme environments
– CH4
– Halophiles
– Thermophiles
• No Antibiotic sensitivity (!)
• 70S ribosomes
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