II. Cells of Bacteria and Archaea
• 2.5 Cell Morphology
• 2.6 Cell Size and the Significance of Being
Small
2.5 Cell Morphology
• Morphology = cell shape
• Major cell morphologies (Figure 2.11)
– Coccus (pl. cocci): spherical or ovoid
– Rod: cylindrical shape
– Spirillum: spiral shape
• Cells with unusual shapes
– Spirochetes, appendaged bacteria, and filamentous
bacteria
Coccus
Rod
Spirillum
Spirochete
Stalk
Hypha
Budding and appendaged bacteria
Filamentous bacteria
Figure 2.11
2.5 Cell Morphology
• Morphology typically does not predict
physiology, ecology, phylogeny, etc. of a
prokaryotic cell
• May be selective forces involved in setting the
morphology
– Optimization for nutrient uptake (small cells and
those with high surface-to-volume ratio)
– Swimming motility in viscous environments or near
2.6 Cell Size and the Significance of Being Small
• Size range for prokaryotes: 0.2 µm to >700 µm
in diameter
– Most cultured rod-shaped bacteria are between 0.5
and 4.0 µm wide and < 15 µm long
– Examples of very large prokaryotes
• Epulopiscium fishelsoni (Figure 2.12a)
• Thiomargarita namibiensis (Figure 2.12b)
• Size range for eukaryotic cells: 10 to >200 µm
in diameter
3/r
2.6 Cell Size and the Significance
of Being Small
• Surface-to-volume ratios, growth rates, and
evolution
– Advantages to being small (Figure 2.13)
• Small cells have more surface area relative to cell volume
than large cells (i.e., higher S/V)
» Support greater nutrient exchange per unit cell volume
» Tend to grow faster than larger cells
Figure 2.12
Rickettsia Smallest
E. Coli
0.1 M
Average Size 0.5 X 1.5 M
Epulopisicum fishelsoni 660 M
Convoluted
Thiomargarita 100X (66000 M)
Heidi Schulz 1997
Vacuoles
ED: Sulfur (S°)
TEA: NO3
III. The Cytoplasmic Membrane
and Transport
• 2.7 Membrane Structure
• 2.8 Membrane Functions
• 2.9 Nutrient Transport
2.7 Membrane Structure
• Cytoplasmic membrane
– Thin structure that surrounds the cell
– Vital barrier that separates cytoplasm from
environment
– Highly selective permeable barrier; enables
concentration of specific metabolites and
excretion of waste products
2.7 Membrane Structure
• Composition of membranes
– General structure is phospholipid bilayer (Figure 2.14)
• Contain both hydrophobic and hydrophilic components
– Can exist in many different chemical forms as a result
of variation in the groups attached to the glycerol
backbone
– Fatty acids point inward to form hydrophobic
environment; hydrophilic portions remain exposed to
external environment or the cytoplasm
Glycerol
Fatty acids
Phosphate
Ethanolamine
Hydrophilic
region
Fatty acids
Hydrophobic
region
Hydrophilic
region
Glycerophosphates
Fatty acids
Figure 2.14
2.7 Membrane Structure
• Cytoplasmic membrane (Figure 2.15)
– 8–10 nm wide
– Embedded proteins
– Stabilized by hydrogen bonds and hydrophobic
interactions
– Mg2+ and Ca2+ help stabilize membrane by
forming ionic bonds with negative charges on
the phospholipids
– Somewhat fluid
Sterol
Cholesterol
All sterols contain the same four rings*
Hopanoid
2.7 Membrane Structure
• Membrane proteins
– Outer surface of cytoplasmic membrane can interact with a variety of
proteins that bind substrates or process large molecules for transport
– Inner surface of cytoplasmic membrane interacts with proteins
involved in energy-yielding reactions and other important cellular
functions
– Integral membrane proteins
• Firmly embedded in the membrane
– Peripheral membrane proteins
• One portion anchored in the membrane
2.7 Membrane Structure
• Archaeal membranes
– Ether linkages in phospholipids of Archaea (Figure
2.16)
– Bacteria and Eukarya that have ester linkages in
phospholipids
– Archaeal lipids lack fatty acids; have isoprenes
instead
– Major lipids are glycerol diethers and tetraethers
(Figure 2.17a and b)
– Can exist as lipid monolayers, bilayers, or mixture
(Figure 2.17)
Ester
Bacteria
Eukarya
Ether
Archaea
Figure 2.16
2.8 Membrane Function
• Permeability barrier (Figure 2.18)
– Polar and charged molecules must be
transported
– Transport proteins accumulate solutes against
the concentration gradient
• Protein anchor
– Holds transport proteins in place
• Energy conservation
– Generation of proton motive force
Functions of the cytoplasmic membrane
Permeability barrier:
Prevents leakage and functions as a
gateway for transport of nutrients into,
and wastes out of, the cell
Protein anchor:
Site of many proteins that participate in
transport, bioenergetics, and chemotaxis
Energy conservation:
Site of generation and dissipation of the
proton motive force
Figure 2.18
2.9 Nutrient Transport
• Carrier-mediated transport systems (Figure
2.19)
– Show saturation effect
– Highly specific
Transporter saturated
Transport
Simple diffusion
Figure 2.19
2.9 Nutrient Transport
• Three major classes of transport systems in
prokaryotes (Figure 2.20)
– Simple transport
– Group translocation
– ABC system
• All require energy in some form, usually
proton motive force or ATP
In
Out
Simple transport:
Driven by the energy
in the proton motive
force
Transported
substance
Group translocation:
Chemical modification
of the transported
substance driven by
phosphoenolpyruvate
P
R~ P
1
2
ABC transporter:
Periplasmic binding
proteins are involved
and energy comes
from ATP.
3
ATP ADP + Pi
Figure 2.20
2.9 Nutrient Transport
• Three transport events are possible:
uniport, symport, and antiport (Figure 2.21)
– Uniporters transport in one direction across the
membrane
– Symporters function as co-transporters
– Antiporters transport a molecule across the
membrane while simultaneously transporting
another molecule in the opposite direction
Figure 2.21
2.9 Nutrient Transport
• The phosphotransferase system in E. coli
(Figure 2.22)
– Type of group translocation: substance transported is
chemically modified during transport across the
membrane
– Best-studied system
– Moves glucose, fructose, and mannose
– Five proteins required
– Energy derived from phosphoenolpyruvate
Glucose
Out
Cytoplasmic
membrane
Nonspecific components
PE
Enz
IIc
P
Enz
I
Pyruvate
Specific components
HPr
Enz
IIa
Direction
of glucose
transport
Enz
IIb
P
P
Direction of P transfer
In
P
Glucose 6_P
Figure 2.22
2.9 Nutrient Transport
• ABC (ATP-binding cassette) systems (Figure 2.23)
– >200 different systems identified in prokaryotes
– Often involved in uptake of organic compounds (e.g., sugars, amino
acids), inorganic nutrients (e.g., sulfate, phosphate), and trace metals
– Typically display high substrate specificity
– Gram-negatives employ periplasmic-binding proteins and ATPdriven transport proteins
– Gram-positives employ substrate-binding proteins and membrane
transport proteins
IV. Cell Walls of Bacteria and
Archaea
• 2.10 Peptidoglycan
• 2.11 LPS: The Outer Membrane
• 2.12 Archaeal Cell Walls
Cell wall characteristics
Elastic
Confers Rigidity
Interior Pressure - Turgor Pressure
Permeable to Salts
Plasmolysis 10-20 % sucrose
Water  Swelling
2.10 Peptidoglycan
• Species of Bacteria separated into two
groups based on Gram stain
• Gram-positives and gram-negatives have
different cell wall structure (Figure 2.24)
– Gram-negative cell wall
• Two layers: LPS and peptidoglycan
– Gram-positive cell wall
• One layer: peptidoglycan
Figure 2.24
2.10 Peptidoglycan
• Peptidoglycan (Figure 2.25)
– Rigid layer that provides strength to cell wall
– Polysaccharide composed of:
•
•
•
•
N-acetylglucosamine and N-acetylmuramic acid
Amino acids
Lysine or diaminopimelic acid (DAP)
Cross-linked differently in gram-negative bacteria
and gram-positive bacteria (Figure 2.26)
CELL WALL
Procaryotes:
GM +
GM -
peptidoglycan (thick layer) NAG/NAM*
peptidoglycan (thin layer) NAG/NAM*
Mycoplasma - no cell wall
Archaea - lacking peptidoglycan – PTG
PTG = protein pseudo-peptidoglycan
N-Acetyl
group
Peptide
cross-links
Lysozymesensitive
bond
Glycan tetrapeptide
N-Acetylglucosamine ( G ) N-Acetylmuramic acid( M )
L-Alanine
D-Glutamic acid
Diaminopimelic
acid
D-Alanine
Figure 2.25
2.10 Peptidoglycan
• Gram-positive cell walls (Figure 2.27)
– Can contain up to 90% peptidoglycan
– Common to have teichoic acids (acidic
substances) embedded in their cell wall
• Lipoteichoic acids: teichoic acids covalently bound
to membrane lipids
Peptidoglycan
cable
Wall-associated
protein
Teichoic acid
Cytoplasmic membrane
Peptidoglycan
Lipoteichoic
acid
Figure 2.27
2.10 Peptidoglycan
• Prokaryotes that lack cell walls
– Mycoplasmas
• Group of pathogenic bacteria
– Thermoplasma
• Species of Archaea
2.11 LPS: The Outer Membrane
• Total cell wall contains ~10% peptidoglycan
• Most of cell wall composed of outer membrane,
aka lipopolysaccharide (LPS) layer
• LPS consists of core polysaccharide and Opolysaccharide (Figure 2.28)
• LPS replaces most of phospholipids in outer half of outer
membrane (Figure 2.29)
• Endotoxin: the toxic component of LPS
Figure 2.28
Endotoxins Lipid A
2.11 LPS: The Outer Membrane
• Periplasm: space located between
cytoplasmic and outer membranes (Figure
2.29)
– ~15 nm wide
– Contents have gel-like consistency
– Houses many proteins
• Porins: channels for movement of
hydrophilic
low-molecular-weight substances (Figure
2.11 LPS: The Outer Membrane
• Structural differences between cell walls of
gram-positive and gram-negative Bacteria
are responsible for differences in the Gram
stain reaction
2.12 Archaeal Cell Walls
• No peptidoglycan
• Typically no outer membrane
• Pseudomurein
– Polysaccharide similar to peptidoglycan (Figure
2.30)
– Composed of N-acetylglucosamine and Nacetylalosaminuronic acid
– Found in cell walls of certain methanogenic Archaea
• Cell walls of some Archaea lack pseudomurein
2.12 Archaeal Cell Walls
• S-Layers
– Most common cell wall type among Archaea
– Consist of protein or glycoprotein
– Paracrystalline structure (Figure 2.31)
Figure 2.31
V. Other Cell Surface Structures
and Inclusions
•
•
•
•
2.13 Cell Surface Structures
2.14 Cell Inclusions
2.15 Gas Vesicles
2.16 Endospores
2.13 Cell Surface Structures
• Capsules and slime layers
– Polysaccharide layers (Figure 2.32)
• May be thick or thin, rigid or flexible
– Assist in attachment to surfaces
– Protect against phagocytosis
– Resist desiccation
Cell Capsule
Figure 2.32
2.13 Cell Surface Structures
• Fimbriae
– Filamentous protein structures (Figure 2.33)
– Enable organisms to stick to surfaces or form
pellicles
Flagella
Fimbriae
Figure 2.33
2.13 Cell Surface Structures
• Pili
–
–
–
–
Filamentous protein structures (Figure 2.34)
Typically longer than fimbriae
Assist in surface attachment
Facilitate genetic exchange between cells
(conjugation)
– Type IV pili involved in twitching motility
Viruscovered
pilus
Figure 2.34
2.14 Cell Inclusions
• Carbon storage polymers
– Poly-β-hydroxybutyric acid (PHB): lipid (Figure 2.35)
– Glycogen: glucose polymer
• Polyphosphates: accumulations of inorganic phosphate (Figure
2.36a)
• Sulfur globules: composed of elemental sulfur (Figure 2.36b)
• Carbonate minerals: composed of barium, strontium, and
magnesium (Figure 2.37)
• Magnetosomes: magnetic storage inclusions (Figure 2.38)
Inclusion Bodies
Organic or Inorganic Bodies Visible by Microscope
Organic Inclusion Bodies
Glycogen- Carbon storage
PHB -Poly-B- Hydroxybutrate
Inorganic Compounds
Polyphosphate - PP
Sulfur-- Granules
Sulfur
Polyphosphate
Figure 2.36
Figure 2.38
Figure 2.39
Figure 2.40
2.15 Gas Vesicles
• Molecular structure of gas vesicles
– Gas vesicles are composed of two proteins,
GvpA and GvpC (Figure 2.41)
– Function by decreasing cell density
Ribs
GvpA
GvpC
Figure 2.41
2.16 Endospores
• Endospores
– Highly differentiated cells resistant to heat,
harsh chemicals, and radiation (Figure 2.42 )
– “Dormant” stage of bacterial life cycle (Figure
2.43)
– Ideal for dispersal via wind, water, or animal
gut
– Present only in some gram-positive bacteria
Figure 2.42
Vegetative cell
Developing
endospore
Sporulating cell
Mature endospore
Figure 2.43
2.16 Endospores
• Endospore structure (Figure 2.45)
–
–
–
–
Structurally complex
Contains dipicolinic acid
Enriched in Ca2+
Core contains small acid-soluble spore proteins
(SASP)
Dipicolinic Acid
Spores
Survival, not multiplication
Resistant to heat, UV, chemicals, desiccation
Bacillus spp. - aerobic
Clostridium spp. - anaerobic
Bacillus anthracis
Clostridium botulinum
Clostridium tetani
VI. Microbial Locomotion
• 2.17 Flagella and Swimming Motility
• 2.18 Gliding Motility
• 2.19 Chemotaxis and Other Taxes
2.17 Flagella and Swimming
Motility
• Flagella: structure that assists in swimming
– Different arrangements: peritrichous, polar,
lophotrichous (Figure 2.48)
– Helical in shape
Figure 2.48
2.17 Flagella and Swimming
Motility
• Flagellar structure of Bacteria
– Consists of several components (Figure 2.51)
– Filament composed of flagellin
– Move by rotation
• Flagellar structure of Archaea
– Half the diameter of bacterial flagella
– Composed of several different proteins
– Move by rotation
15–20 nm
L
Filament
P
MS
Flagellin
Hook
Outer
membrane
(LPS)
L Ring
Rod
P Ring
Periplasm
Peptidoglycan
+ + ++
+ + ++
MS Ring
Basal
body
C Ring
− − −−
Cytoplasmic
membrane
Mot protein
− − −−
Fli proteins
(motor switch)
Mot protein
45 nm
Rod
MS Ring
Mot
protein
C Ring
Figure 2.51
2.17 Flagella and Swimming
Motility
• Flagellar synthesis
– Several genes are required for flagellar
synthesis and motility (Figure 2.53)
– MS ring is made first
– Other proteins and hook are made next
– Filament grows from tip
2.17 Flagella and Swimming
Motility
• Flagella increase or decrease rotational
speed in relation to strength of the proton
motive force
• Differences in swimming motions (Figure
2.54)
– Peritrichously flagellated cells move slowly in a
straight line
– Polarly flagellated cells move more rapidly and
typically spin around
Tumble − flagella
pushed apart
(CW rotation)
Bundled
flagella
(CCW rotation)
Flagella bundled
(CCW rotation)
Peritrichous
Reversible flagella
CCW rotation
CW rotation
Unidirectional flagella
CW rotation
Cell
stops,
reorients
CW rotation
Polar
Figure 2.54
2.18 Gliding Motility
• Gliding motility
–
–
–
–
–
Flagella-independent motility (Figure 2.56)
Slower and smoother than swimming
Movement typically occurs along long axis of cell
Requires surface contact
Mechanisms
• Excretion of polysaccharide slime
• Type IV pili
• Gliding-specific proteins
In
Cytoplasmic
membrane
Peptidoglycan
Outer
membrane
Out
Movement of cell
Glide proteins
Movement of outer
Surface
membrane glide proteins
Figure 2.56
2.19 Chemotaxis and Other
Taxes
• Taxis: directed movement in response to
chemical or physical gradients
–
–
–
–
–
Chemotaxis: response to chemicals
Phototaxis: response to light
Aerotaxis: response to oxygen
Osmotaxis: response to ionic strength
Hydrotaxis: response to water
2.19 Chemotaxis and Other
Taxes
• Chemotaxis
– Best studied in E. coli
– Bacteria respond to temporal, not spatial,
difference in chemical concentration
– “Run and tumble” behavior (Figure 2.57)
– Attractants and receptors sensed by
chemoreceptors
Tumble
Attractant
Tumble
Run
Run
No attractant present: Random
movement
Attractant present: Directed
movement
Figure 2.57
VII. Eukaryotic Microbial Cells
• 2.20 The Nucleus and Cell Division
• 2.21 Mitochondria, Hydrogenosomes, and
Chloroplast
• 2.22 Other Major Eukaryotic Cell
Structures
2.20 The Nucleus and Cell
Division
• Eukaryotes
– Contain a membrane-enclosed nucleus and
other organelles (e.g., mitochondria, Golgi
complex, endoplasmic reticula, microtubules,
and microfilaments (Figure 2.60)
Microtubules
Mitochondrion
Smooth endoplasmic reticulum
Rough endoplasmic
reticulum
Flagellum
Cytoplasmic
membrane
Ribosomes
Mitochondrion
Microfilaments
Lysosome
Golgi complex
Chloroplast
Nuclear envelope
Nucleus
Nuclear pores
Nucleolus
Figure 2.60
2.20 The Nucleus and Cell
Division
• Nucleus: contains the chromosomes (Figure
2.61)
–
–
–
–
DNA is wound around histones (Figure 2.61b)
Visible under light microscope without staining
Enclosed by two membranes
Within the nucleus is the nucleolus
• Site of ribosomal RNA synthesis
Double-stranded DNA
Nucleus
Nuclear
pores
Vacuole
Lipid
vacuole
Nucleosome core
Histone H1
Mitochondria
Core histones
Figure 2.61
•
2.20 The Nucleus and Cell
Cell division
Division
– Mitosis
• Normal form of nuclear division in eukaryotic cells
• Chromosomes are replicated and partitioned into two
nuclei (Figure 2.62)
• Results in two diploid daughter cells
– Meiosis
• Specialized form of nuclear division
• Halves the diploid number to the haploid number
Figure 2.62
.21 Mitochondria, Hydrogeno2somes, and Chloroplast
• All specialize in energy metabolism
– Mitochondria (Figure 2.63)
• Respiration and oxidative phosphorylation
• Bacterial dimensions (rod or spherical)
• Over 1,000 per animal cell
• Surrounded by two membranes
• Folded internal membranes called cristae
– Contain enzymes needed for respiration and ATP production
• Innermost area of mitochondrion called matrix
– Contains enzymes for the oxidation of organic compounds
Ribosomes
Structure double stranded DNA
Each Strand is monomers connected by condensation RX
sugar of one connected to the Phosphate of the other
Covalent phosphodiester bond
Two stands are anti-parallel held together H-bonds
complementary base pairs (bp)
A= T
G=C
molecule twisted to form helix
Central Dogma of Cell Biology* DNA RNA Protein
Nucleic acids
Nucleic acids are composed of nucleotides
can occur as monomers or polymers
Components of nucleotide:
1. Sugar
2. Nitrogen containing base
3. Phosphate group
Structural differences between DNA and RNA
1. Different sugars: deoxyribose & ribose
2. Different N-bases: A,C,G,T vs A,C,G,U
3. DS vs SS
Plasmids
•Not Essential to growth
•Genes that enhance the survivability
•Antibiotic resistance
•Sex pili
•Conjugation
•F+