Chapter 4 Part 2
Cell Wall
Purpose/significance
– Protection from lysis
– Cell shape
– Differentiation
– Anchor flagella
– Virulence (LPS—Gram Negative)
Rigidity and Complexity
Peptidoglycan (common to all bacteria)
– Sugar backbone (NAM-NAG), tetrapeptide side
chains, peptide crossbridge
Gram + versus Gram –
Thick PTGN Thinner PTGN
No techoic Acids
Techoic Acids
LPS Outer membrane
No LPS outer – Lipoprotein
membrane – Porins
No periplasm Periplasm
Peptidoglycan Sugar
Backbone
Repeating
disaccharide units:
NAM and NAG
Peptidoglycan Structure
NAM-NAG backbone
Side chain and cross bridge amino acids connect
layers of NAM-NAG backbones
Gram Positive Cell Wall
Ptgn protection
– Thermal lysis
Techoic acids
– Role in cell wall growth
– Regulates movement of cations in and out of cell wall
Gram Negative Cell Wall
Cell Wall protection
– More susceptible to thermal lysis than Gram pos.
– Less susecptible to antimicrobial chemical agents
Outer membrane
– Porin proteins, lipoproteins, lipopolysaccharide (O
polysaccharide and lipid A), phospholipid, periplasmic
proteins.
Outer Membrane Structures
Phospholipid bilayer:
– Evade phagocytosis (strong
negative charge)
– Barrier to some antibiotics and
digestive enzymes
Porin proteins
– passage of some compounds
Lipopolysaccharide
– Endotoxins of pathogens
Periplasmic proteins
– Transport enzymes (transport
nutrients)
– Digestive enzymes (Preliminary
digestion)
Mycoplasma and Archaea
Mycoplasma: No cell wall and unique plasma membrane
Archaea variety of cell wall types
– No ptgn
– Pseudomurein
– S Layer (peptide)
Cell Wall Damage
Lysozyme
– Protoplast versus spheroplast
Osmotic lysis susceptibility
Cell wall is the target for many antibiotics
(penicillin)
– Prevents cell wall synthesis
Plasma Membrane
Prokaryotes versus Eukaryotes
– Why do they differ? How do they differ?
Basic Structure
– Phospholipid bilayer
Surfaces: Polar head (hydrophilic) contains phosphate
group and glycerol
Internal: nonpolar tail (hydrophobic) composed of
fatty acids
– Integral membrane proteins
Transport of nutrients, receptors, aquaporins
– Peripheral proteins
Fluid Mosaic Model
Plasma Membrane
Plasma Membrane:
Functions
Semi-permeable membrane
– Passage of needed molecules (nutrients, water, etc.) and
barrier to harmful chemicals
– Passage through bilayer
Small molecules, hydrophobic, non-charged
Give me examples
– Passage through transport proteins
Only specific molecules (usually larger, hydrophilic or charged)
Breakdown of nutrients
Energy production
Photosynthetic enzymes (for autotrophs)
Transport: Review on
Your own
Passive Transport
– Diffusion
– Facilitated diffusion
– Osmosis
Active Transport
– Uniport
– Symport
– Antiport
Inside of Prokaryotic Cell
Cytoplasm
– 80% water
– Contains all internal structures
Nuclear region contains DNA
– Not membrane bound
– Circular single bacterial chromosome (4,300 genes)
– Weakly bound to proteins in PM (help to replicate and separate during
cell division)
– 20% of cell
Plasmids
– Can contain 1 or more
– Extrachromosomal DNA (5-100 genes)
– Often transferred to other prokaryotes (conjugation)
– Contains non-essential genes
antibiotic resistance
Inside of Prokaryotes
Prokaryotic ribosomes
– Site of protein synthesis
– Protein and RNA
– 70S ribosome: 30S and 50S
subunits
– What does S represent?
Inclusion bodies
– Dependent on species
– Lipid inclusions for energy
– Polyphosphate to save for ATP
– gas vacuoles for buoyancy (air
filled)
– Polysaccharide (starch or
glycogen) granules for energy
– Magnetosomes (iron oxide)
Prokaryotic Ribosome
Endospores
Highly durable
– Heat resistance
– Dehydration
resistance
– UV resistant
Survival mechanism
for some species
– Bacillus and
Clostridium spp.
Vegetative cell
versus endospore
Sporulation:
Nutrient and water level low
UV light
Decreased Temperature
Vegetative Endospore
Cell
Spore Germination:
Nutrient and water level increase
Increased Temperature
Figure 4.21: Formation of endospores by sporulation.
Cytoplasm 1 Spore septum begins to isolate newly replicated
Cell wall DNA and a small portion of cytoplasm.
Plasma
membrane
Bacterial
chromosome
(DNA)
(a) Sporulation, the process of endospore formation
Figure 4.21: Formation of endospores by sporulation.
Cytoplasm 1 Spore septum begins to isolate newly replicated
Cell wall DNA and a small portion of cytoplasm.
2 Plasma membrane starts to
Plasma surround DNA, cytoplasm, and
membrane membrane isolated in step 1 .
Bacterial
chromosome
(DNA)
(a) Sporulation, the process of endospore formation
Figure 4.21: Formation of endospores by sporulation.
Cytoplasm 1 Spore septum begins to isolate newly replicated
Cell wall DNA and a small portion of cytoplasm.
2 Plasma membrane starts to
Plasma surround DNA, cytoplasm, and
membrane membrane isolated in step 1 .
Bacterial
chromosome
(DNA)
(a) Sporulation, the process of endospore formation
3 Spore septum surrounds isolated portion,
forming forespore.
Two
membranes
Figure 4.21: Formation of endospores by sporulation.
Cytoplasm 1 Spore septum begins to isolate newly replicated
Cell wall DNA and a small portion of cytoplasm.
2 Plasma membrane starts to
Plasma surround DNA, cytoplasm, and
membrane membrane isolated in step 1 .
Bacterial
chromosome
(DNA)
(a) Sporulation, the process of endospore formation
3 Spore septum surrounds isolated portion,
forming forespore.
Two
membranes
4 Peptidoglycan layer forms
between membranes.
Figure 4.21: Formation of endospores by sporulation.
Cytoplasm 1 Spore septum begins to isolate newly replicated
Cell wall DNA and a small portion of cytoplasm.
2 Plasma membrane starts to
Plasma surround DNA, cytoplasm, and
membrane membrane isolated in step 1 .
Bacterial
chromosome
(DNA)
(a) Sporulation, the process of endospore formation
3 Spore septum surrounds isolated portion,
forming forespore.
Two
membranes
4 Peptidoglycan layer forms
between membranes.
5 Spore coat forms.
Figure 4.21: Formation of endospores by sporulation.
Cytoplasm 1 Spore septum begins to isolate newly replicated
Cell wall DNA and a small portion of cytoplasm.
2 Plasma membrane starts to
Plasma surround DNA, cytoplasm, and
membrane membrane isolated in step 1 .
Bacterial
chromosome
(DNA)
(a) Sporulation, the process of endospore formation
3 Spore septum surrounds isolated portion,
forming forespore.
Two
membranes
4 Peptidoglycan layer forms
between membranes.
5 Spore coat forms.
6 Endospore is freed from cell.
Figure 4.21: Formation of endospores by sporulation.
Cytoplasm 1 Spore septum begins to isolate newly replicated
Cell wall DNA and a small portion of cytoplasm.
2 Plasma membrane starts to
Plasma surround DNA, cytoplasm, and
membrane membrane isolated in step 1 .
Bacterial
chromosome
(DNA)
(a) Sporulation, the process of endospore formation
3 Spore septum surrounds isolated portion,
forming forespore.
Two
membranes
4 Peptidoglycan layer forms
Endospore
between membranes.
1 µm
(b) An endospore in Bacillus anthracis
5 Spore coat forms.
6 Endospore is freed from cell.