The Bacterial Cell

1
Dr. Alvin Fox
The Bacterial Cell
2
Key Words
Prokaryotic
Outer membrane
Eubacteria (Bacteria)
Periplasmic space
Oxidative phosphorylation
Eukaryotic
Spheroplast/protoplast
Plasmid
Flagella
Chromosome
Chemotaxis
Ribosome
Axial filament
Peptidoglycan (murein, mucopeptide)
Periplasmic binding protein
Gram stain
Permeases
Gram negative
Storage Granules
Gram positive
Pili (fimbriae)
Cell envelope
Capsule (slime layer, glycocalyx)
Cell membrane
Endospore (spore)
Cell wall
3
PROKARYOTES
BACTERIA
ARCHAEA
EUKARYOTES
4
Prokaryotes (Bacteria)
Eubacter "True" bacteria
human pathogens
clinical or environmental
one kingdom
Archaea
Environmental organisms
second kingdom
5
Eukaryotes
Other cell-based life e.g.
plants
animals
fungi
6

Prokaryotic Cell (versus Eukaryotic Cell)

Not compartmentalized
Cell membranes lack sterols (e.g. cholesterol)
Single circular chromosome
Ribosomal are 70S
- subunits
30S (16S rRNA)
50S (5S & 23S rRNA)
7
Bacteria versus Archaebacteria
Eubacteria
peptidoglycan (murein)
muramic acid

Archaebacteria
pseudomurein
no muramic acid



8
Bacteria versus Archaebacteria
16S rRNA
sequence different
9
Eukaryotic cell
Prokaryotic cell
Gram +
Gram -
Cell wall
Rough endoplasmic
reticulum
Mitochondria
(e.g. animal)
Nucleoid
Nucleus
Cell membrane
Cytoplasm
Flagellum
10
Bacteria
Plasmids
Extra-chromosomal DNA

multiple copy number

coding
- pathogenesis factors
- antibiotic resistance factors

bacterial replication

11
The Cell Envelope
Gram Stain
Gram Positive
Gram Negative
12
Cytoplasm
Oxidative phosphorylation occurs at cell membrane
(since there are no mitochondria).
Cell membrane
The cell wall is outside of cell membrane
rigid, protecting cell from osmotic lysis.
Cell Wall
13
GRAM POSITIVE
GRAM NEGATIVE
Cytoplasm
Cytoplasm
Lipoteichoic acid
Peptidoglycan-teichoic acid
Cytoplasmic membrane
Inner (cytoplasmic) membrane
Outer Membrane
Lipopolysaccharide
Porin
Braun lipoprotein
Periplasmic space
14
Outer Membrane
Gram negative bacteria
major permeability barrier
space between inner and outer membrane
periplasmic space
store degradative enzymes
Gram positive bacteria
no periplasmic space
15
GRAM NEGATIVE
CELL ENVELOPE
Cytoplasm
Inner (cytoplasmic) membrane
Outer Membrane
(Major permeability barrier)
Lipopolysaccharide
Porin
Braun lipoprotein
Periplasmic space
Degradative enzyme
Periplasmic binding protein
Permease
16
Cytoplasm
Lipoteichoic acid
Peptidoglycan-teichoic acid
Cytoplasmic membrane
GRAM POSITIVE
CELL ENVELOPE
Degradative enzyme
17
FLAGELLA
Some bacteria are motile
Locomotory organelles- flagella
Taste environment
Respond to food/poison
chemotaxis
18
Flagella
embedded in cell membrane
project as strand
Flagellin (protein) subunits
move cell by propeller like action

19
Axial filaments

spirochetes
similar function to flagella
run lengthwise along cell
snake-like movement
20
Making Wall-less forms
Result from action of:
enzymes lytic for cell wall
antibiotics inhibiting peptidoglycan biosynthesis

Usually non-viable

Wall-less bacteria that don’t replicate:
spheroplasts (with outer membrane)
protoplasts (no outer membrane).

Wall-less bacteria that replicate
L forms
21
Naturally Wall-less Genus
Mycoplasma
22
Pili (fimbriae)
hair-like projections of the cell
sexual conjugation
adhesion to host epithelium

23
Capsules and slime layers
outside cell envelope
well defined: capsule
not defined: slime layer or glycocalyx
usually polysaccharide
often lost during in vitro culture
protective in vivo
24
Endospores (spores)
Dormant cell
Produced when starved
Resistant to adverse conditions
- high temperatures
- organic solvents
contain calcium dipicolinate
Bacillus and Clostridium