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Chapter 4:
Functional Anatomy of
Prokaryotic and Eukaryotic
Cells
Prokaryote
Pre-nucleus
Eukaryote
True nucleus
• One circular chromosome,
not in a membrane
• Paired chromosomes, in
nuclear membrane
• No histones
• Histones bound to DNA
• No membrane-bound
organelles
• Membrane-bound
organelles
• Complex cell walls
• Simpler cell walls
• Binary fission
• Mitosis
(peptidoglycan in bacteria)
(polysaccharide)
Prokaryotic Cells: Morphology
• Average size:
0.2 -2.0 µm in diameter
2.0-8.0 µm in length
• Basic shapes/morphologies:
Coccus (spherical)
Bacillus* (rod-shaped)
Coccobacillus
Spiral
Prokaryotic cells: Arrangements
Pairs: diplodiplococci
diplobacilli
Chains: streptostreptococci
streptobacilli
Clusters: staphylostaphylococci
Prokaryotic cells:
Structures external to the cell wall
Prokaryotic cell structures:
Glycocalyx
• Capsule: Glycocalyx firmly
attached to the cell wall
• Sticky outer coat
• Polysaccharide and/or polypeptide
composition
Figure 4.6a
• Aids in attachment of cell to a
substrate
• Helps prevent dehydration
• Impairs phagocytosis (host
defense mechanism)
http://lecturer.ukdw.ac.id/dhira/BacterialStructure/SurfaceStructs.html
Prokaryotic cell structures:
Flagella
• Cellular propellers
• Three basic parts
• Filament: Made of
chains of flagellin
protein
• Hook
• Basal body: anchor
to the cell wall and
membrane
• Rotation in the basal
body propels the cell
Figure 4.8
Prokaryotic cell structures: Flagella
Flagella Arrangement
( flagella at both poles)
(tuft from one pole)
(flagella distributed over the entire cell)
Figure 4.7
Prokaryotic cell structures: Flagella
Motility
Taxis: movement toward
or away from a stimulus
-chemotaxis
-phototaxis
Figure 4.9
Prokaryotic cell structures:
Flagella
Motile E. coli with flourescently-labelled flagella from
the Roland Institute at Harvard
Prokaryotic cell structures:
Axial Filaments
• Axial filaments=
endoflagella
• Spirochete movement
• Anchored at one end of a
cell
• Contained within an
outer sheath
• Rotation causes cell to
move
• Spiral/corkscrew motion
Figure 4.10a
Prokaryotic cell structures:
Fimbriae and Pili
• Composed of protein
pilin
• Fimbriae allow
attachment to
surfaces/other cells
• Few to hundreds
per cell
• Pili are used to
transfer DNA from one
cell to another
• Longer, 1-2 per cell
Figure 4.11
Prokaryotic cells:
The cell wall
Prokaryotic cell structures:
Cell Wall
• Main functions of the cell wall
• Prevents osmotic lysis
• Helps maintain cell shape
• Point of anchorage for flagella
• Contains peptidoglycan (in bacteria)
Prokaryotic cell structures: Cell Wall
Peptidoglycan (or murein)
Macromolecular network:
• Polymer of a repeating disaccharide unit (backbone)
• Backbones linked by polypeptides
Figure 4.13a
Prokaryotic cell structures:
Gram-positive Cell Walls
Gram-positive cell wall
• Thick PG layer; rigid structure
• Teichoic acids:
• Lipoteichoic acid links PG to plasma membrane
• Wall teichoic acid links PG sheets
• Polysaccharides & teichoic acids are cellular antigens
Prokaryotic cell structures:
Gram-negative Cell Walls
Gram-negative
cell wall
• Thin PG layer
• Surrounded by an outer membrane
• Protection from phagocytes, some antibiotics
• Periplasm (contains PG, degradative enzymes, toxins)
• Lipopolysaccharide (LPS)
• O polysaccharide antigen
• Lipid A is called endotoxin
• Porins (proteins) form channels through membrane
Figure 4.13b, c
Prokaryotic cell structures:
Cell Walls
Gram-positive
Gram-negative
cell walls
cell walls
• Thick peptidoglycan
• Thin peptidoglycan
• Teichoic acids
• No teichoic acids
• Outer membrane
• Lipopolysaccharide
• Porins
Gram stain mechanism
• Step 1: Crystal violet (primary stain)
• Enters the cytoplasm (stains) both cell types
• Step 2: Iodine (mordant)
• Forms crystals with crystal violet (CV-I complexes)
that are too large to diffuse across the cell wall
• Step 3: Alcohol wash (decolorizer)
• Gm +: dehydrates PG, making it more impermeable
• Gm -: dissolves outer membrane and pokes small
holes in thin PG through which CV-I can escape
• Step 4: Safranin (counterstain)
• Contrasting color to crystal violet
Prokaryotic cell structures: Cell Wall
Atypical Cell Walls
• Mycoplasma
• Smallest known bacteria
• Lack cell walls
• Sterols in plasma membrane protect from lysis
• Acid-fast cells (Mycobacterium and Nocardia genera)
• Mycolic acid (waxy lipid) layer outside of PG resists
typical dye uptake
• Archaea
• Wall-less, or
• Walls of pseudomurein (altered polysaccharide and
polypeptide composition vs. PG)
Prokaryotic cell structures: Cell Wall
Damage to Cell Walls
• Lysozyme attacks disaccharide bonds in peptidoglycan
• Penicillin inhibits peptide cross-bridge formation in
peptidoglycan
• Bacteria with weakened cell walls are very
susceptible to osmotic lysis
Prokaryotic cells:
Structures internal to the cell wall
Prokaryotic cell structures:
Plasma Membrane
• Phospholipid bilayer
• Proteins
• Fluid Mosaic Model
• Membrane is as viscous as olive oil
• Proteins move to function
• Phospholipids rotate and move laterally
Figure 4.14b
Prokaryotic cell structures:
Plasma Membrane
Main function: selective barrier
• Selective permeability allows passage of select
molecules
• Small molecules (H2O, O2, CO2, some sugars)
• Lipid-soluble molecules (nonpolar organic)
Prokaryotic cell structures:
Plasma Membrane
Movement across membranes:
Passive Processes
• Passive processes do not require energy (ATP)—
involves movement down a concentration gradient
• Simple diffusion: Movement of a solute from an
area of high concentration to an area of low
concentration
• Facilitated diffusion: Solute combines with a
transporter protein to move down its gradient
• Osmosis: Diffusion of water down its gradient
• Diffusion continues until the solute is evenly
distributed (state of equilibrium)
Prokaryotic cell structures:
Plasma Membrane
• Osmosis: Movement of water across a selectively permeable
membrane from an area of higher water concentration to
an area of lower water concentration
• Water moving down its concentration gradient
Figure 4.18
Prokaryotic cell structures:
Plasma Membrane
Three types of osmotic solutions:
Isotonic solution
[sol]solution = [sol]cell
Hypotonic solution*
[sol]solution < [sol]cell
Osmotic lysis
[sol]cell = concentration of solute inside the cell
Hypertonic solution
[sol]solution > [sol]cell
Plasmolysis
Figure 4.18c-e
Prokaryotic cell structures:
Plasma Membrane
Movement across membranes:
Active Transport Processes
• Active transport of substances requires a transporter protein
and ATP
• Solute movement
up/against its
concentration
gradient
• Important when
nutrients are scarce
Prokaryotic cell structures:
Other Internal Structures
• Cytoplasm: substance inside plasma membrane
• 80% water, contains mainly proteins, carbohydrates,
lipids, inorganic ions and low-molecular weight
compounds
• Chromosomal DNA: single circular string of doublestranded DNA attached to the plasma membrane
• Located in the “nucleoid” area of the cell
• Plasmids: small, circular, extrachromosomal DNA
• Genes encoded typically not required for survival under
normal conditions
Prokaryotic cell structures:
Other Internal Structures
• Ribosomes: machinery for protein synthesis
(translation)
• Tens of thousands of ribosomes per cell
Complete 70S ribosome
Prokaryotic cell structures:
Other Internal Structures
Inclusions: Reserve deposits
Type:
Contents:
• Metachromatic granules
(volutin)
•Phosphate reserves (for ATP
generation)
• Polysaccharide granules
•Energy reserves
• Lipid inclusions
•Energy reserves
• Sulfur granules
•Energy reserves
• Carboxysomes
•Ribulose 1,5-diphosphate
carboxylase for CO2 fixation
• Gas vacuoles
•Protein covered cylinders
• Magnetosomes
•Iron oxide
(destroys H2O2)
Prokaryotic cell structures:
Other Internal Structures
Endospores
• Specialized resting cells (metabolically inactive)
• Resistant to desiccation, heat, chemicals
• Can remain dormant for thousands of years
• Bacillus, Clostridium genera only (Gram-positive)
• Sporulation: Endospore formation
• Triggered by deficiency of a key nutrient
• Germination: Return to vegetative state
• Triggered by physical/chemical
damage to endospore’s coat
http://qlab.com.au
Stained pus from a mixed anaerobic infection
www.textbookofbacteriology.net
Functional Anatomy of Eukaryotic Cells
Figure 4.22
Functional Anatomy of Eukaryotic Cells:
Flagella and Cilia
• Contain cytoplasm, enclosed by plasma membrane
• Move in a wavelike motion
Figure 4.23
Functional Anatomy of Eukaryotic Cells:
Flagella and Cilia
Figure 4.23a, b
Functional Anatomy of Eukaryotic Cells:
Cell Walls and Glycocalyx
• Cell walls
• Plants, algae, fungi
• Polysaccharide; simpler than prokaryotic cell walls
• Glycocalyx
• Carbohydrates extending from animal plasma
membrane
• Anchored to cell membrane
• Strengthens surface, aids in attachment
Functional Anatomy of Eukaryotic Cells:
Plasma Membrane
Similar to prokaryotic PM structure and function:
• Phospholipid bilayer
• Selective permeability
• Peripheral proteins
• Passive transport processes
• Integral proteins
• Active transport processes
EXCEPT, they contain
• Sterols (complex lipids, help strengthen membrane)
• Site for endocytosis (phagocytosis and pinocytosis)
Functional Anatomy of Eukaryotic Cells:
Cytoplasm
• Cytoplasm
Substance inside plasma
membrane and outside nucleus
• Cytoskeleton
Microfilaments,
intermediate filaments,
microtubules
• Contains organelles
Specialized functions
(nucleus, ER, Golgi complex,
mitochondria, lysosomes,
ribosomes)
Functional Anatomy of Eukaryotic Cells:
Ribosomes
• Larger, denser than prokaryotic
• Eukaryotic ribosomes: 80S
Prokaryotic ribosomes: 70S
• Membrane-bound pool
(attached to ER)
• Free pool (in cytoplasm)
Functional Anatomy of Eukaryotic Cells:
Nucleus
• Storage for almost whole
cell’s genetic information
• Enclosed by nuclear
envelope
• Proteins bound to DNA
(histones and nonhistones)
Figure 4.24
Functional Anatomy of Eukaryotic Cells:
Mitochondrion
• Contains DNA and ribosomes
(70S)
• Double membrane
• Inner membrane folds:
cristae
• Portion inside of inner
membrane: matrix
• Proteins involved in
respiration and ATP
production in cristae and
matrix
• Chloroplasts: enzymes for lightgathering necessary for
photosynthesis
Figure 4.27
Endosymbiotic Theory
• Theory on evolution of eukaryotic cells’ organelles
• Prokaryotes: 3.5-4 byo
• Eukaryotes: ~2.5 byo
• Mitochondria and chloroplasts share properties with prokaryotes
• Reproduce independently of cell
• Size/shape
• Circular DNA
• Their ribosomes are 70S