Transcript Prokaryotic and Eukaryotic

Chapter 3
Cell Structure
and Function
© 2012 Pearson Education Inc.
Lecture prepared by Mindy Miller-Kittrell
North Carolina State University
Cell Morphology
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3 main shapes
Rod (bacillus)
Sphere (coccus)
Spiral (spirilla)
Processes of Life
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Growth
Reproduction
Responsiveness
Metabolism—chemical reactions in the cell.
Building up and breaking down molecules.
© 2012 Pearson Education Inc.
Prokaryotic and Eukaryotic Cells: An Overview
• Prokaryotes
– Lack nucleus
– Lack various internal structures bound with
phospholipid membranes
– Are small (~1.0 µm in diameter) micrometers
– Have a simple structure
– Include bacteria and archaea
© 2012 Pearson Education Inc.
Figure 3.2 Typical prokaryotic cell
Inclusions
Ribosome
Cytoplasm
Flagellum
Nucleoid
Glycocalyx
Cell wall
Cytoplasmic membrane
Prokaryotic and Eukaryotic Cells: An Overview
• Eukaryotes
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Have nucleus
Have internal membrane-bound organelles
Are larger (10–100 µm in diameter)
Have more complex structure
Include algae, protozoa, fungi, animals, and
plants
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Figure 3.3 Typical eukaryotic cell
Nuclear envelope
Nuclear pore
Nucleolus
Lysosome
Mitochondrion
Centriole
Secretory vesicle
Golgi body
Cilium
Transport vesicles
Ribosomes
Rough endoplasmic
reticulum
Smooth endoplasmic
reticulum
Cytoplasmic
membrane
Cytoskeleton
Figure 3.4 Approximate size of various types of cells
Virus
Orthopoxvirus
0.3 m diameter
Bacterium
Staphylococcus
1 m diameter
Chicken egg
4.7 cm diameter
(47,000 m)*
Parasitic protozoan
Giardia
14 m length
*Actually, the inset box on the egg would
be too small to be visible.
(Width of box would be about 0.002 mm.)
External Structures of Bacterial Cells
• Glycocalyces
– Gelatinous, sticky substance surrounding the
outside of the cell
– Composed of polysaccharides, polypeptides,
or both
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External Structures of Bacterial Cells
• Two Types of Glycocalyces
– Capsule
– Firmly attached to cell surface
– May prevent bacteria from being recognized by host
– Slime layer
– Loosely attached to cell surface
– Sticky layer allows prokaryotes to attach to surfaces
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Figure 3.5 Glycocalyces-overview
Glycocalyx
(capsule)
Glycocalyx
(slime layer)
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 3.7 Micrographs of basic arrangements of bacterial flagella-overview
Figure 3.8 Axial filament-overview
Endoflagella
rotate
Axial filament
Axial filament
rotates around
cell
Outer
membrane
Cytoplasmic
membrane
Spirochete
corkscrews
and moves
forward
Axial filament
External Structures of Bacterial Cells
• Flagella
– Function
– Rotation propels bacterium through environment
– Rotation reversible; can be counterclockwise or
clockwise
– Bacteria move in response to stimuli (taxis—
phototaxis or chemotaxis)
– Runs
– Tumbles
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Figure 3.9 Motion of a peritrichous bacterium
Attractant
Run
Tumble
Run
Tumble
External Structures of Bacterial Cells
• Fimbriae and Pili
– Rodlike proteinaceous extensions
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External Structures of Bacterial Cells
• Fimbriae
– Sticky, bristlelike projections
– Used by bacteria to adhere to one another, to
hosts, and to substances in environment
– Shorter than flagella
– Serve an important function in biofilms
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Figure 3.10 Fimbriae
Flagellum
Fimbria
External Structures of Bacterial Cells
• Pili
– Special type of fimbria
– Also known as conjugation pili
– Longer than other fimbriae but shorter than
flagella
– Bacteria typically have only one or two per cell
– Mediate the transfer of DNA from one cell to
another (conjugation)
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Figure 3.11 Pili
Conjugation pilus
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
– Cell wall of bacteria can be targeted 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 3.12 Bacterial shapes and arrangements-overview
Bacterial Cell Walls
• Gram-Positive Bacterial Cell Walls
– Relatively thick layer of peptidoglycan
– Appear purple following Gram staining procedure
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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
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
Cytoplasmic
membrane
Phospholipid layers
Lipopolysaccharide
(LPS)
O side chain
(varies In
length and
composition)
Integral
proteins
Core
polysaccharide
Lipid A
(embedded
in outer
membrane)
Periplasmic space
Fatty acid
Comparison of Gram positive and Gram negative cells
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
Bacterial Cytoplasmic Membranes
• Function
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Energy storage
Harvest light energy in photosynthetic bacteria
Selectively permeable
Naturally impermeable to most substances
Proteins allow substances to cross membrane
Maintain concentration gradient
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Bacterial Cytoplasmic Membranes
• Function
– Passive processes
– Diffusion
– Facilitated diffusion
– Osmosis
– Active processes
– Active transport
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Figure 3.20 Effects of isotonic, hypertonic, and hypotonic solutions on cells-overview
Cells without a wall
(e.g., mycoplasmas,
animal cells)
H2O
H2O
H2O
Cell wall
Cells with a wall
(e.g., plants, fungal
and bacterial cells)
Cell wall
H2O
H2O
Cell membrane
Isotonic solution
H2O
Cell membrane
Hypertonic solution
Hypotonic solution
Cytoplasm of Bacteria
• Cytosol – Liquid portion of cytoplasm
• Endospores – Unique structures produced by
some bacteria that are a defensive strategy
against unfavorable conditions
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Cytoplasm of Bacteria
• Nonmembranous Organelles
– Ribosomes
– Sites of protein synthesis
– 70S—consists of 50S large subunit and 30S small
subunit.
– Cytoskeleton
– Plays a role in forming the cell’s basic shape
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External Structures of Archaea
• Glycocalyces
– Adhere cells to one another and inanimate objects
• Flagella
• Fimbriae and Hami
– Many archaea have fimbriae
– Some make fimbriae-like structures called hami
– Function to attach archaea to surfaces
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Figure 3.26 Archaeal hami
Hamus
Grappling
hook
Prickles
Archaeal Cell Walls and Cytoplasmic Membrane
– Most archaea have cell walls
– Do not have peptidoglycan
– Contain variety of specialized polysaccharides
and proteins
– All archaea have cytoplasmic membranes
– Maintain chemical gradients
– Control import and export of substances from the
cell
– Lipids lack phosphate (not phospholipids).
© 2012 Pearson Education Inc.
Figure 3.27 Representative shapes of archaea-overview
Cytoplasm of Archaea
– Archaeal cytoplasm similar to bacterial cytoplasm
– Have 70S ribosomes
– Fibrous cytoskeleton
– Circular DNA
– Archaeal cytoplasm also differs from bacterial
cytoplasm
– Different ribosomal proteins
– Different metabolic enzymes to make RNA
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External Structure of Eukaryotic Cells
• Glycocalyces
– Never as organized as prokaryotic capsules
– Help anchor animal cells to each other
– Provide protection against dehydration
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Eukaryotic Cell Walls
– Fungi, algae, plants, and some protozoa have
cell walls
– Composed of various polysaccharides
– Plant cell walls composed of cellulose
– Fungal cell walls usually composed of chitin.
– Algal cell walls composed of a variety of
polysaccharides.
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Eukaryotic Cytoplasmic Membranes
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All eukaryotic cells have cytoplasmic membrane
Are a fluid mosaic of phospholipids and proteins
Contain steroid lipids to help maintain fluidity
Control movement into and out of cell
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Figure 3.30 Endocytosis-overview
Pseudopodium
Cytoplasm of Eukaryotes
• Flagella
– Structure and arrangement
– Differ structurally and functionally from prokaryotic
flagella
– Function
– Do not rotate but undulate rhythmically
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Figure 3.31a Eukaryotic flagella and cilia
Flagellum
Figure 3.31b Eukaryotic flagella and cilia
Cilia
Cytoplasm of Eukaryotes
• Cilia
– Shorter and more numerous than flagella
– Coordinated beating propels cells through their
environment
– Also used to move substances past the surface
of the cell
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Cytoplasm of Eukaryotes
• Other Nonmembranous Organelles
– Ribosomes
– Larger than prokaryotic ribosomes (80S versus 70S)
– Composed of 60S and 40S subunits
– Cytoskeleton
– Extensive network of fibers and tubules
– Anchors organelles
– Produces basic shape of the cell
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