microbial cell structure and functions
TRANSCRIPT
© 2015 Pearson Education, Inc.
Microbial cell structure and functions
Course_ Gneral Microbiology
Lec. no_ 2nd lecture
2nd Grade – Fall Semester 2021-2022
Instructor´s name_ Heshu Jalal Instructor´s email_ Heshu.jalal @tiu.edu.iq
© 2015 Pearson Education, Inc.
II. Cells of Bacteria and Archaea
• 2.5 Cell Morphology
• 2.6 Cell Size and the Significance of Being Small
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2.5 Cell Morphology
• Morphology = cell shape
• Major cell morphologies (Figure 2.11)
• Coccus (pl. cocci): spherical or ovoid
• Rod: cylindrical shape (bacillus/bacilli)
• Spirillum: spiral shape
• Cells with unusual shapes
• Spirochetes, appendaged bacteria, and filamentous
bacteria
• Many variations on basic morphological types
© 2015 Pearson Education, Inc. Figure 2.11
Coccus
Rod
Spirillum
Spirochete
Stalk Hypha
Filamentous bacteria
Budding and appendaged bacteria
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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
© 2015 Pearson Education, Inc. Figure 2.13
© 2015 Pearson Education, Inc.
III. The Cytoplasmic Membrane and Transport
(aka Plasma Membrane)
• 2.7 Membrane Structure
• 2.8 Membrane Functions
• 2.9 Nutrient Transport
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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
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2.7 Membrane Structure
• Composition of membranes
• General structure is phospholipid bilayer (Figure 2.14)
• Contain both hydrophobic and hydrophilic components
• Fatty acids point inward to form hydrophobic
environment; hydrophilic portions remain exposed to
external environment or the cytoplasm
© 2015 Pearson Education, Inc. Figure 2.14
Fatty acids
Phosphate
Ethanolamine
Fatty acids
Hydrophilic
region
Hydrophobic
region
Hydrophilic
region
Glycerophosphates
Fatty acids
Glycerol
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2.7 Membrane Structure
• Cytoplasmic membrane (Figure 2.15)
• 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
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Phospholipids
6–8 nm
Integral
membrane
proteins
Hydrophilic
groups
Hydrophobic
groups
Phospholipid
molecule
Out
In
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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
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2.7 Membrane Structure
• Archaeal membranes
• Ether linkages in phospholipids of Archaea
• Bacteria and Eukarya that have ester linkages in
phospholipids
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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
© 2015 Pearson Education, Inc. Figure 2.18
Functions of the cytoplasmic membrane
Permeability barrier:Prevents leakage and functions as agateway 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
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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
© 2015 Pearson Education, Inc. Figure 2.20
Out In
R~
2
3
Transported
substance
P
P
ATP ADP + Pi
Simple transport:
Driven by the energy
in the proton motive
Force (H+ gradient)
Group translocation:
Chemical modification
of the transported
substance driven by
phosphoenolpyruvate
ABC transporter:
Binding
proteins are involved
and energy comes
from ATP.
1
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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
© 2015 Pearson Education, Inc. Figure 2.21
© 2015 Pearson Education, Inc.
IV. Cell Walls of Bacteria and Archaea
• 2.10 Peptidoglycan
• 2.11 LPS: The Outer Membrane
• 2.12 Archaeal Cell Walls
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2.10 Peptidoglycan-the Wonder Wall
• Species of Bacteria separated into two groups
based on Gram stain reaction
• Gram-positives and gram-negatives have different
cell wall structure (Figure 2.24)
• Gram-negative cell wall
• Two parts: LPS and peptidoglycan
• Gram-positive cell wall
• One part: peptidoglycan
© 2015 Pearson Education, Inc. Figure 2.24
© 2015 Pearson Education, Inc.
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
© 2015 Pearson Education, Inc. Figure 2.27
Peptidoglycan
cable
Teichoic acid Peptidoglycan Lipoteichoic
acid
Cytoplasmic membrane
Wall-associated
proteinTeichoic acid
and
Lipoteichoic
acid-
Structural-
linkers and
stiffeners
Wall proteins
may be
enzymes,
receptors or
attachment
molecules
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2.10 Peptidoglycan
• Prokaryotes that lack cell walls
Mycoplasmas
• Group of pathogenic bacteria
Species of Archaea
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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 replaces most of phospholipids in outer half of outer
membrane (Figure 2.29)
• Endotoxin: the toxic component of LPS
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O-specific
polysaccharideCore polysaccharide
Lipid A Protein
Lipopolysaccharide
(LPS)
Phospholipid
Porin
Lipoprotein
8 nm
Out
Cell Wall or
Envelope
Outer
membrane
Periplasm
Cytoplasmic
membrane
Peptidoglycan
In
Figure 2.29
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2.11 LPS: The Outer Membrane
• Periplasm: space located between cytoplasmic
and outer membranes (Figure 2.29)
• Contents have gel-like consistency
• Houses many proteins
• Porins: channels for movement of hydrophilic
low-molecular-weight substances
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2.12 Archaeal Cell Walls
• Some Archaea have cell walls, some do not
• When present, walls are different from Bacterial
cell walls
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2.12 Archaeal Cell Walls
• S-Layers
• Most common cell wall type among Archaea but may
also be found in Bacteria
• Consist of protein or glycoprotein
• Network of proteins/glycoproteins attached to outer
surface of plasma membrane
• Has openings or “pores”
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2.12 Archaeal Cell Walls
• No peptidoglycan (no Wonder Wall)
• Typically no outer membrane
• Pseudomurein aka pseudopeptidoglycan
• Polysaccharide similar to peptidoglycan
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V. Other Cell Surface Structures and Inclusions
• 2.13 Cell Surface Structures
• 2.14 Gas Vesicles
• 2.15 Endospores
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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
• External to cell
• In Gram + and –
• Not part of LPS outer membrane
© 2015 Pearson Education, Inc. Figure 2.32
Cell Capsule
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2.13 Cell Surface Structures• Fimbriae
• Filamentous protein (curlin, adhesin) structures for
attachment
• Enable organisms to stick to surfaces
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2.13 Cell Surface Structures
• Pili
• Filamentous protein (pilin) structures
• Typically longer than fimbriae
• Facilitate genetic exchange between cells (conjugation)
• Some types are involved in motility.
© 2015 Pearson Education, Inc. Figure 2.34
Virus-
covered
pilus
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2.14 Gas Vesicles
• Gas vesicles
• Confer buoyancy in
planktonic cells
• Spindle-shaped, gas-filled
structures made of protein
• Impermeable to water
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2.16 Endospores
• Endospores
• Highly differentiated cells resistant to heat, harsh
chemicals, and radiation
• “Dormant” stage of bacterial life cycle.
• may persist for decades in environment (soil)
• Ideal for dispersal via wind, water, or animal gut
• Present only in some gram-positive bacteria
© 2015 Pearson Education, Inc. Figure 2.42
© 2015 Pearson Education, Inc.
VI. Microbial Locomotion
• 2.17 Flagella and Swimming Motility
• 2.18 Gliding Motility
• 2.19 Chemotaxis and Other Taxes
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2.17 Flagella and Swimming Motility
• Flagella: structures that assists in swimming
• Different arrangements: (a) peritrichous, (b) polar,
(c) lophotrichous
• Helical organization
• Very different from a eukaryotic flagellum
© 2015 Pearson Education, Inc. Figure 2.48
Peritrichous Polar Lophotrichous
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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
© 2015 Pearson Education, Inc. Figure 2.51
15–20 nm
Filament
Flagellin
L
P
MS
HookOuter
membrane
(LPS)
L
Ring
P
Ring
Rod
PeptidoglycanPeriplasm
MS Ring
Basal
body
C Ring
Cytoplasmic
membrane
Fli proteins
(motor switch)
Mot proteinMot protein
45 nm
Rod
MS Ring
C Ring
Mot
protein
+ + + + + + + +
− − − − − − − −
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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
• Gliding proteins
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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
© 2015 Pearson Education, Inc.