Chapter 4:
Functional Anatomy of Prokaryotic and Eukaryotic Cells
Prokaryote Eukaryote
• One circular chromosome, not in a membrane
• No histones
• No membrane-bound organelles
• Complex cell walls (peptidoglycan in bacteria)
• Binary fission
• Paired chromosomes, in nuclear membrane
• Histones bound to DNA
• Membrane-bound organelles
• Simpler cell walls (polysaccharide)
• Mitosis
Pre-nucleus True nucleus
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) Spiral
Coccobacillus
Pairs: diplo- diplococci diplobacilli
Chains: strepto- streptococci streptobacilli
Clusters: staphylo-staphylococci
Prokaryotic cells: Arrangements
Prokaryotic cells:Structures external to the cell wall
• Capsule: Glycocalyx firmly attached to the cell wall
• Sticky outer coat
• Polysaccharide and/or polypeptide composition
• Aids in attachment of cell to a substrate
• Helps prevent dehydration
• Impairs phagocytosis (host defense mechanism)
Prokaryotic cell structures: Glycocalyx
Figure 4.6a
http://lecturer.ukdw.ac.id/dhira/BacterialStructure/SurfaceStructs.html
• 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
Figure 4.7
( flagella at both poles)
(tuft from one pole) (flagella distributed over the entire cell)
Flagella ArrangementProkaryotic cell structures: Flagella
Figure 4.9
Taxis: movement toward or away from a stimulus-chemotaxis-phototaxis
Prokaryotic cell structures: Flagella
Motility
Prokaryotic cell structures: Flagella
Motile E. coli with flourescently-labelled flagella from the Roland Institute at Harvard
• 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: Axial Filaments
• 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 cell structures: Fimbriae and Pili
Prokaryotic cells:The 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
Macromolecular network:
• Polymer of a repeating disaccharide unit (backbone)
• Backbones linked by polypeptides
Prokaryotic cell structures: Cell WallPeptidoglycan (or murein)
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
Figure 4.13b, c
Gram-negative cell wall
Prokaryotic cell structures: Gram-negative Cell Walls
• 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
• Thick peptidoglycan
• Teichoic acids
• Thin peptidoglycan
• No teichoic acids
• Outer membrane
• Lipopolysaccharide
• Porins
Gram-positive cell
walls
Gram-negative cell
walls
Prokaryotic cell structures: Cell Walls
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
• 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
Atypical 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 cell structures: Cell Wall
Damage to Cell Walls
Prokaryotic cells:Structures internal to the cell wall
• 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
Prokaryotic cell structures:Plasma Membrane
• 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)
Movement across membranes:Passive Processes
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
Osmotic lysis Plasmolysis
Figure 4.18c-e
Prokaryotic cell structures:Plasma Membrane
[sol]solution = [sol]cell [sol]solution > [sol]cell[sol]solution < [sol]cell
Isotonic solution
[sol]cell = concentration of solute inside the cell
Hypotonic solution* Hypertonic solution
Three types of osmotic solutions:
Prokaryotic cell structures:Plasma Membrane
• Active transport of substances requires a transporter protein and ATP
• Solute movement up/against its concentrationgradient
• Important when nutrients are scarce
Movement across membranes:Active Transport Processes
• 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 double-stranded 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
Prokaryotic cell structures:Other Internal Structures
Complete 70S ribosome
Prokaryotic cell structures:Other Internal Structures
Type:
• Metachromatic granules (volutin)
• Polysaccharide granules
• Lipid inclusions
• Sulfur granules
• Carboxysomes
• Gas vacuoles
• Magnetosomes
Contents:
•Phosphate reserves (for ATP generation)
•Energy reserves
•Energy reserves
•Energy reserves
•Ribulose 1,5-diphosphate carboxylase for CO2 fixation
•Protein covered cylinders
•Iron oxide (destroys H2O2)
Inclusions: Reserve deposits
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
www.textbookofbacteriology.net
Stained pus from a mixed anaerobic infection
Functional Anatomy of Eukaryotic Cells
Figure 4.22
• Contain cytoplasm, enclosed by plasma membrane
• Move in a wavelike motion
Figure 4.23
Functional Anatomy of Eukaryotic Cells: Flagella and Cilia
Functional Anatomy of Eukaryotic Cells: Flagella and Cilia
Figure 4.23a, b
• 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: Cell Walls and Glycocalyx
Functional Anatomy of Eukaryotic Cells: Plasma Membrane
Similar to prokaryotic PM structure and function:
• Phospholipid bilayer
• Peripheral proteins
• Integral proteins
EXCEPT, they contain
• Sterols (complex lipids, help strengthen membrane)
• Site for endocytosis (phagocytosis and pinocytosis)
• Selective permeability
• Passive transport processes
• Active transport processes
• 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: Cytoplasm
• 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: Ribosomes
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 light-gathering 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