Transcript PROCARYOTIC AND EUCARYOTIC CELLS

BACTERIAL
MORPHOLOGY:
PROCARYOTIC AND
EUCARYOTIC CELLS
Chapter 4
Eucaryotic cells
• any organism with a fundamental cell
type containing membraneenclosed organelles
Prokaryotic Cells
• Comparing Prokaryotic and
Eukaryotic Cells
–Prokaryote comes from the
Greek words for prenucleus.
–Eukaryote comes from the Greek
words for true nucleus.
Prokaryote
Eukaryote
• One circular
• Paired
chromosome, not
in a membrane
• No histones
• No organelles
• Peptidoglycan cell
walls
• Binary fission
chromosomes, in
nuclear membrane
• Histones
• Organelles
• Polysaccharide cell
walls
• Mitotic spindle
Procaryotes (Bacteria)
• Average size: 0.2 -1.0 µm  2 - 8 µm
• Basic shapes:
Protozoan (eucaryote)
Procaryotic cells
• any organism with a fundamental
cell type without nucleus
• Unusual shapes
–Star-shaped Stella
–Square Haloarcula
• Most bacteria are monomorphic
• A few are pleomorphic
Figure 4.5
Bacteria (procaryote)
Procaryotic cells (cont.)
• Bacteria
–Differentiation by:
•Morphology, composition,
nutritional requirements,
and biochemical activities
and source of energy
Shapes of bacteria
• coccus (spheres)
• bacillus (rods)
• spiral (twisted)
• pleomorphic (several)
Arrangements
• Pairs: diplococci,
diplobacilli
• Clusters:
staphylococci
• Chains: streptococci,
streptobacilli
Arrangements of cocci
• Divide in:
–one plane=diplococci
–two planes=tetrads
–three planes=sarcineae
–multiple=staphylococci
Structures external to the
bacterial cell wall
•Glycocalyx
•Flagella
•Axial filaments
•Fimbriae and pili
Glycocalyx
• Capsule (firm) or slime layer
(loose)
–polysaccharide and/or
polypeptide
–Inhibits phagocytosis
–Attaches to host surfaces
–Protects against desiccation
Glycocalyx
• Outside cell wall
• Usually sticky
• A capsule is neatly organized
• A slime layer is unorganized
& loose
• Extracellular polysaccharide
allows cell to attach
• Capsules prevent
phagocytosis
Figure 4.6a, b
Bacterial
glycocalyx
Streptococcus pneumoniae
capsule
Flagella
• Outside cell wall
• Made of chains of
flagellin
• Attached to a
protein hook
• Anchored to the
wall and
membrane by the
basal body
• They propel
bacteria around
Flagella
Motile Cells
• Rotate flagella to run or
tumble
• Move toward or away from
stimuli (taxis)
• Flagella proteins are H
antigens
(e.g., E. coli O157:H7)
Lophotrichous
Monotrichous
Peritrichous
Types of Flagella
Types of Flagella
Main function: to propel bacteria to and from
area’s of nutrients/toxic environments
Types of Flagella
Axial filaments
• Present in spiral cells
• Similar to flagella, but they wrap around
the cell
• Corkscrew motion enables a bacterium
such as T.pallidum (causative agent of
Syphilis) to move effectively through body
fluids (vaginal secretions)
Fimbriae, pili and sex pili
•Short thin appendages
–Fimbriae and pili
•Help cells to adhere to
surfaces
–Sex pili
•Bridge between bacterial
cells for DNA transfer
DNA transfer
through a sex pili
Fimbriae
• Fimbriae allow
attachment to
teeth, stones in
creeks, plastic
catheter's in
hospitals
• Pili are used to
transfer DNA
from one cell to
another
Fimbriae
Intestinal mucosa
E. coli
Cell wall
•Surrounds the plasma
membrane
–Protects the cell from
osmotic pressure changes
–Lattice formed by
peptidoglycan (murein)
Cell Wall
• Prevents osmotic lysis
• Made of peptidoglycan (in bacteria)
Figure 4.6a, b
Peptidoglycan (murein)
•N-acetylglucosamine
(NAG)
•N-acetylmuramic acid
(NAM)
–repeating disaccharides
joined by polypeptides
Peptidoglycan
• Polymer of disaccharide
N-acetylglucosamine (NAG) & Nacetylmuramic acid (NAM)
• Linked by polypeptides
Figure 4.13a
N-acetylglucosamine
(NAG)
N-acetymuramic acid
(NAM)
Peptide bridge
NAG
NAM
Peptide bridge
Gram-positive cells
•several well-organized
peptidoglycan layers
•teichoic acids
Gram positive
Gram positive
S. aureus
Gram-Positive cell walls
• Teichoic acids:
– Lipoteichoic acid links to plasma membrane
– Wall teichoic acid links to peptidoglycan
• May regulate movement of cations
• Polysaccharides provide antigenic variation
Figure 4.13b
Gram Negative Cells
Gram-negative cells
• a thin poorly-organized peptidoglycan
layer
• outer membrane
– lipoprotein-lipopolysaccharide-phospholipid
(LPS)
Gram-negative cells (cont.)
•outer membrane
–protects against
phagocytosis, penicillin
sugars in LPS act as
antigens
lipid A acts as
endotoxin
Gram negative bacteria
Outer membrane
peptidoglycan
Figure 4.13b, c
Gram negative
E. coli
Gram positive
No outer membrane
Gram negative
With an outer
membrane
Gram-Negative Outer Membrane
• Lipopolysaccharides, lipoproteins,
phospholipids.
• Forms the periplasm between the outer
membrane and the plasma membrane.
• Protection from phagocytes, complement,
antibiotics.
• O polysaccharide antigen, e.g., E. coli O157:H7.
• Lipid A is an endotoxin.
• Porins (proteins) form channels through
membrane
• Thick
• Thin
peptidoglycan
peptidoglycan
• Teichoic acids • No teichoic acids
• In acid-fast
• Outer membrane
cells, contains
mycolic acid
Figure 4.13b, c
Atypical Cell Walls
•Mycoplasmas
–Lack cell walls
–Sterols in plasma membrane
•Archaea
–Wall-less, or
–Walls of pseudomurein (lack
NAM and D amino acids)
Damage to Cell Walls
• Lysozyme digests disaccharide in
peptidoglycan
• Penicillin inhibits peptide bridges in
peptidoglycan
Damage to cell walls
• Lysozyme degrades
peptidoglycans
• Penicillin and other
antibiotics affect
synthesis of cell wall
Plasma Membrane
Plasma Membrane
Figure 4.14a
Plasma Membrane
• Phospholipid bilayer
• Peripheral proteins
• Integral proteins
• Transmembrane proteins
Figure 4.14b
Fluid Mosaic Model
• Membrane is as
viscous as olive oil.
• Proteins move to
function
• Phospholipids rotate
and move laterally
Figure 4.14b
THE GRAM STAIN
Gram Stain Mechanism
• Crystal violet-iodine crystals form in cell
• Gram-positive
– Alcohol dehydrates peptidoglycan
– CV-I crystals do not leave
• Gram-negative
– Alcohol dissolves outer membrane and leaves
holes in peptidoglycan
– CV-I washes out
Gram stain technique
Gram positive
Gram negative
Know all four steps and why you
are doing them!!!
REVIEW
• We are conditioned to think of
bacteria as invisable, potentially
harmful little creatures!!
• Actually, relatively few species of
bacteria cause disease in humans,
animals and plants!!
• After this course you will realize that
without bacteria, much of life as we
know it would not be possible !!
Procaryotes
Bacteria and
Archaea Bacteria
The Prokaryotes:
Domains Bacteria and Archaea
• One circular chromosome, not in
a membrane
• No histones
• No organelles
• Peptidoglycan cell walls
• Binary fission
THE PROTEOBACTERIA
• Remember all organisms made up of
eukaryotic cells probably evolved from
bacterialike organism, which were the
earliest forms of life!!!
• Include most of the G-,
chemoheterotrophic bacteria
• Have arisen from a common
photosynthetic ancestor
Domain Bacteria
• Proteobacteria
–Mythical
Greek god,
Proteus, who
could
assume
many shapes
–Gramnegative
Alpha (a)--Proteobacteria
• Are capable of growth at very low
levels of nutrients
• Have unusual morphology,
including protrusions such as
stalks or buds known as
prosthecae
• They include agriculturally
important bacteria capable of
inducing nitrogen fixation
The a (alpha) Proteobacteria
• Human pathogens:
–Bartonella
–B.hensela Cat-scratch disease
–Brucella
Brucellosis
Rickettsias
• Rickettsias, Coxiella and Chlamydia
are obligate intracellular parasites
• They only reproduce inside a
mammalian cell
The a (alpha) Proteobacteria
• Obligate intracellular parasites:
– Ehrlichia - Tick-borne, ehrlichiosis
– Rickettsia - Arthropod-borne,
spotted fevers
•R. prowazekii  Epidemic typhus
(lice)
•R. typhi Endemic murine typhus
(rat fleas)
•R. rickettsii  Rocky Mountain
Spotted Fever(ticks)
The a (alpha) Proteobacteria
(Rickettsias)
Figure 11.1
The a (alpha) Proteobacteria
• Wolbachia. Live in insects
and other animals
• Belongs to the Rickettsia
genera
The a (alpha) Proteobacteria
• Have prosthecae:
– Caulobacter. Stalked
bacteria found in low
nutrient lakes as well as in
laboratory waterbaths—
stalk helps in the
absorption of nutrients
– Hyphomicrobium. Budding
bacteria found in lakes—
when nutrients are low,
stalk size increases to
provide greater area for
nutrient absorption
The a (alpha) Proteobacteria
• Plant pathogen:
– Agrobacterium
(invades plants &
causes crown gall)
– It inserts a plasmid
into plant cells,
inducing the tumor
– Researchers are
very interested in
this organism b/c
plant cells are very
difficult to
penetrate
The a (alpha) Proteobacteria
• Chemoautotrophic:
–Oxidize nitrogen for energy
–Fix CO2
•Nitrobacter. NH3+  NO2–
•Nitrosomonas. NO2–  NO3–
The a (alpha) Proteobacteria
• Nitrogen-fixing bacteria:
–Azospirillum
•Grow in soil, using
nutrients excreted by
plants
•Fix nitrogen
–Rhizobium
•Fix nitrogen in the
roots of plants
Figure 27.5
The a (alpha) Proteobacteria
• Are industrially important
• They produce acetic acid
(vinegar) from ethyl alcohol:
–Acetobacter
–Gluconobacter