Download Chap 3 Cell Structure Fall 2012

Chapter 3
Cell Structure
and Function
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Processes of Life
What is the difference between a living thing
and a non living thing?
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Figure 3.1 Examples of types of cells-overview
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How are these cells similar?
Prokaryote
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Eukaryote
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External Structures of Bacterial Cells
• Two Types of Glycocalyces
– Capsule
– Composed of organized repeating units of organic
chemicals
– Firmly attached to cell surface
– May prevent bacteria from being recognized by host
– Slime layer
– Loosely attached to cell surface
– Water soluble
– Sticky layer allows prokaryotes to attach to surfaces
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Figure 3.5 Glycocalyces-overview
Glycocalyx
(capsule)
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Glycocalyx
(slime layer)
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External Structures of Bacterial Cells
• Flagella
– Are responsible for movement
– Have long structures that extend beyond cell
surface
– Are not present on all bacteria
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Figure 3.6 Proximal structure of bacterial flagella-overview
Filament
Direction
of rotation
during run
Rod
Peptidoglycan
layer (cell wall)
Protein rings
Cytoplasmic
membrane
Cytoplasm
Filament
Gram 
Outer
protein
rings
Rod
Gram 
Basal
body
Outer
membrane
Peptidoglycan
layer
Integral
protein
Inner
protein
rings
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Integral
protein
Cytoplasm
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Cell
wall
Cytoplasmic
membrane
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External Structures of Bacterial Cells
ANIMATION Flagella: Movement
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Figure 3.7 Micrographs of basic arrangements of bacterial flagella-overview
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Figure 3.8 Axial filament-overview
Endoflagella
rotate
Axial filament
Axial filament
rotates around
cell
Outer
membrane
Cytoplasmic
membrane
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Spirochete
corkscrews
and moves
forward
Axial filament
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Figure 3.10 Fimbriae
Flagellum
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Fimbria
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Figure 3.11 Pili
Conjugation pilus
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Bacterial Cell Walls
• Bacterial Cell Walls
– Provide structure and shape and protect cell from
osmotic forces
– Assist some cells in attaching to other cells or in
resisting antimicrobial drugs
– Can target cell wall of bacteria with antibiotics
– Give bacterial cells characteristic shapes
– Composed of peptidoglycan
– Scientists describe two basic types of bacterial cell
walls, Gram-positive and Gram-negative
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Figure 3.13 Comparison of the structures of glucose, NAG, and NAM-overview
Glucose
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N-acetylglucosamine
NAG
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N-acetylmuramic acid
NAM
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Bacterial Cell Walls
• Gram-Positive Bacterial Cell Walls
– Relatively thick layer of peptidoglycan
– Contain unique polyalcohols called teichoic acids
and lipotechoic acid – have a negative charge
– Appear purple following Gram staining procedure
– Up to 60% mycolic acid in acid-fast bacteria
helps cells survive desiccation
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Figure 3.15a Comparison of cell walls of Gram-positive and Gram-negative bacteria
Peptidoglycan layer
(cell wall)
Cytoplasmic
membrane
Gram-positive cell wall
Lipoteichoic acid
Teichoic acid
Integral
protein
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Bacterial Cell Walls
• Gram-Negative Bacterial Cell Walls
– Have only a thin layer of peptidoglycan
– Bilayer membrane outside the peptidoglycan
contains phospholipids, proteins, and
lipopolysaccharide (LPS)
– May be impediment to the treatment of disease
– Appear pink following Gram staining procedure
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Figure 3.15b Comparison of cell walls of Gram-positive and Gram-negative bacteria
Porin
Outer
membrane
of cell wall
Porin
(sectioned)
Peptidoglycan
layer of cell wall
Gram-negative cell wall
n
Periplasmic space
Cytoplasmic
membrane
Phospholipid layers
Lipopolysaccharide
(LPS)
O side chain
(varies In
length and
composition)
Integral
proteins
Core
polysaccharide
Lipid A
(embedded
in outer
membrane)
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Fatty acid
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Bacterial Cytoplasmic Membranes
• Structure
– Referred to as phospholipid bilayer
– Composed of lipids and associated proteins
– Fluid mosaic model describes current
understanding of membrane structure
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Figure 3.16 The structure of a prokaryotic cytoplasmic membrane: a phospholipid bilayer
Head, which
contains phosphate
(hydrophilic)
Phospholipid
Tail
(hydrophobic)
Integral
proteins
Cytoplasm
Integral
protein
Phospholipid
bilayer
Peripheral protein
Integral protein
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Bacterial Cytoplasmic Membranes
Remember the Functions???
What are they???
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Cytoplasm of Bacteria
• Cytosol – Liquid portion of cytoplasm
• Inclusions – May include reserve deposits of
chemicals
• Endospores – Unique structures produced by
some bacteria that are a defensive strategy
against unfavorable conditions
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Figure 3.23 Granules of PHB in the bacterium Azotobacter chroococcum
Polyhydroxybutyrate
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Figure 3.24 The formation of an endospore-overview
Cell wall
Cytoplasmic
membrane
DNA is replicated.
A cortex of calcium and
dipicolinic acid is
deposited between
the membranes.
DNA
Cortex
Vegetative cell
Spore coat forms
around endospore.
DNA aligns along
the cell’s long axis.
Cytoplasmic membrane
invaginates to form
forespore.
Forespore
Endospore matures:
completion of spore coat
and increase in resistance
to heat and chemicals by
unknown process.
Endospore is released from
original cell.
Cytoplasmic membrane
grows and engulfs
forespore within a
second membrane.
Vegetative cell’s DNA
disintegrates.
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Spore coat
Outer
spore coat
Endospore
Outer
spore coat
First
membrane
Second
membrane
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Cytoplasm of Bacteria
• Nonmembranous Organelles
– Ribosomes
– Sites of protein synthesis
– Cytoskeleton
– Plays a role in forming the cell’s basic shape
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Endosymbiotic Theory
• Mitochondria and chloroplasts have 70S ribosomes,
circular DNA, and two membranes. Why????
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