Download Cell grouping

The Shape of Things = Morphology
Two main shapes of bacteria:
LECTURE 3
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Spheres - cocci (singular = coccus)
PROKARYOTIC CELL
STRUCTURE
Rods - bacilli (singular = bacillus)
Other shapes:
We’ll mostly discuss
Bacteria, more about
Archaea and Eukarya
Later.
Comma shaped - vibrio
Spiral - spirilla, spirochete
Varying shapes - pleomorphic
Unusual cell shapes !"#$%&'()*,
Cell grouping
e.g. Neisseria
Fig. 11.2. Methanosarcina sp. (an Archaea) note the packets of 4 or more cells….
Some Bacteria have even more elaborate morphologies…..
e.g. Streptococcus
e.g. Sarcina
(symmetrical packet of
4 or more cells)
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e.g. Staphylococcus
Fig. 11.7. Complex multicellular morphology in various
cyanobacteria:
a. Spiral trichome of Spirulina
b. Oscillatoria
Fig. 11.19. Filamentous hyphae of an Actinobacterium,
Streptomyces sp. Note multicellular hyphae and spherical spores
(conidia).
Back to a single Bacterial cell….
Fig. 11.18. Very complex
multicellular, macroscopic,
fruiting bodies of the
Myxobacteria.
Fig. 3.23
The Plasma Membrane
Every cell, whether prokaryotic or
eukaryotic, has a plasma membrane.
Very thin -about 8 nm thick
Separates the inside of the cell from the
environment
Current model of membrane structure is the
Fluid-Mosaic model
Functions of the Plasma Membrane:
**It is a permeability barrier - prevents
leakage of cell materials into and out of
cell
It is a device for energy conservation. The
membrane can separate protons (H+) from
hydroxyl ions (OH-) across its surface. This
is called the proton motive force and is
used to generate the cell’s energy
currency, ATP.
Fig. 3.24
Permeability of the Cytoplasmic Membrane: Osmosis
Group Translocation
Fig. 3.25
Generation of Energy: Proton Motive Force
Fig. 3.26
Directed Movement of Molecules
Fig. 3.27
ACTICE TRANSPORT Fig.
Fig. 3.28
Fig. 3.30
Why do bacteria have cell walls?
With all of the dissolved solutes in a cell, the
turgor pressure is about 2 atmospheres - or
about the same pressure as in a car tire!
Cell walls help withstand these pressures and
give the cells shape.
The Structure of Peptidoglycan
Fig. 3.32
Gram positive Cell Walls
Impt. for immune
recognition of
bacteria
Gram negative Cell Walls
Lipopolysaccharide - LPS
Impt. for immune
recognition of
bacteria
Fig. 3.33
Fig. 3.35
How does the Gram stain work?
The best hypothesis is:
Ecological significance of Gram - and
Gram + cell walls?
Which would resist drying better?
Thick peptidoglycan,
pores close, prevent
CV from escaping
Components External to the Cell Wall
Components External to the Cell Wall
Slime layer - unorganized material that is
removed easily
Glycocalyx
Capsule - a layer of well
organized material, not easily
washed off.
S-layer - a regularly structured layer
composed of protein or glycoprotein
May help resist phagocytosis
May perform many functions:
• protect against ionic fluctuations
• protect against predation
• attach to surfaces and other cells
Filamentous protein
appendages
• Flagella
• Pili
Fimbria(e) - pili used to attach to surfaces
Pili (fimbriae)
Pili (sing. = pilus) - larger, genetically
determined by sex factors and used for
mating.
Figure 8.17
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Flagella & Motility
Flagella (sing. = flagellum) are used for
locomotion.
Flagella may be distributed in specific
patterns:
monotrichous
lophotrichous
amphitrichous
peritrichous
Fig. 3.18. Flagella visualized with a stain that coats
them with a thick layer of stain so that they can be
seen with the light microscope.
Fig. 3.38
a. Peritrichous flagella
visualized with a
scanning electron
microscope (SEM)
Flagella are composed of 3 parts:
• the filament
• the basal body
• the hook
b. Polar flagellum
visualized with an
SEM.
Fig. 3.39
The direction of the rotation determines how the cell
moves.
Chemotaxis
In a constant environment, bacteria will move
randomly.
They can, however, exhibit directed movement
toward an attractant (e.g. food) or away from a
repellant (e.g. waste). This is chemotaxis.
See Fig. 3.40
Bacteria rotate their flagella very rapidly - as
much as 1000 rps!
Although bacteria only move 0.00017 km/hr,
this equates to 50-60 cell lengths/sec.
In contrast, a cheetah can only run at a rate of
25 body lengths/sec!
The Cytoplasmic Matrix
Unlike eukaryotes, bacteria do not have
membrane-bound organelles.
The cytoplasmic matrix is the material between
the plasma membrane and the nucleoid.
What’s in there?
• Ribosomes
• Cytoskeleton-like system of proteins
Ribosomes
Storage granules (a type of inclusion body)
RNA + proteins
Some are membrane-bound, most aren’t.
Site of protein synthesis
Used for storage:
• carbon compounds
• inorganic substances
• energy
Reduce osmotic
pressure
Granules
Inclusion Bodies (cont.):
Photosynthetic bacteria have gas vacuoles that
they can fill with air.
This gives them buoyancy so they can stay near
the surface of the water and close to sunlight.
They can regulate their buoyancy by
collapsing vacuoles and constructing new
ones.
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The Nucleoid
How big are bacterial genomes?
Bacteria usually have 1 “chromosome” in an
irregularly shaped region, the nucleoid.
1 million - 10 million base pairs
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If stretched out, the E. coli genome
would be about 1 mm in length, but
the bacteria itself is only 2-3 !m long!
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The DNA in the nucleoid is supercoiled to
package it compactly.
Many bacteria also contain plasmids.
The Endospore
Gram + - very resistant, dormant structure
These are also circular.
Cannot be killed by boiling - must be autoclaved.
Plasmids are typically
Makes them dangerous pathogens, but most
endospore formers are not pathogens.
passed on to all
daughter cells.
They are generally not
essential for survival,
but very often contain
genes that provide a selective advantage,
such as antibiotic resistance.
The structure of an endospore is complex:
Endospore formation
CW = core wall
CX = cortex
SC = spore coat
EX = exosporium
CR = core
N = nucleoid
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Fig. 26.12
Fig. 11.16
Bacillus
anthracis
(spores in
middle of cells)
Clostridium botulinum
(Spores at ends of cells)
Clostridium
tetani
(spores at
ends of cells)