1. Functional Anatomy of Prokaryotic and Eukaryotic Cells
Chapter 4:
Functional Anatomy of Prokaryotic and Eukaryotic Cells

2. Prokaryote Eukaryote One circular chromosome, not in a membrane
Pre-nucleus
True nucleus
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

3. Prokaryotic Cells: Morphology
Average size: µm in diameter
µm in length
Basic shapes/morphologies:
Coccus (spherical)
Bacillus* (rod-shaped)
Spiral
bacteria could fit head-to-head in 1 mm
Coccobacillus

4. Prokaryotic cells: Arrangements
Pairs: diplo diplococci diplobacilli
Chains: strepto- streptococci streptobacilli
Clusters: staphylo-staphylococci

5. Structures external to the cell wall
Prokaryotic cells:
Structures external to the cell wall

6. Prokaryotic cell structures: Glycocalyx
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)
Figure 4.6a

7. 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
Flagella=propellers
Flagellin chains form helix around hollow core
Basal body: rod inserted into 2-4 rings—4 in Gm- cells, 2 in Gm+ cells (inner pair)
Figure 4.8

8. Prokaryotic cell structures: Flagella
Flagella Arrangement
( flagella at both poles)
(tuft from one pole)
(flagella distributed over the entire cell)
Figure 4.7

9. Prokaryotic cell structures: Flagella Motility
Taxis: movement toward or away from a stimulus
-chemotaxis
-phototaxis
Tumbles—reversal of rotation direction
-taxic stimuli detected by receptors in or just under the cell wall
Figure 4.9

10. Prokaryotic cell structures: Flagella
Motile E. coli with flourescently-labelled flagella from the Roland Institute at Harvard

11. 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
-axial filament structure similar to flagella structure
Figure 4.10a

12. 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
-both structures: composed of protein pilin arranged helically around a central core
Transfer of DNA=conjugation
Figure 4.11

13. Prokaryotic cells:
The cell wall

14. 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)
Cell wall protects the plasma membrane and cytosol from adverse changes in the outside environment
-osmotic lysis is rupture of the cell when the water pressure inside the cell is greater than that outside the cell

15. Prokaryotic cell structures: Cell Wall Peptidoglycan (or murein)
Macromolecular network:
Polymer of a repeating disaccharide unit (backbone)
Backbones linked by polypeptides
-repeating disaccharide unit, joined by polypeptideslattice/network that surrounds/protects the cell
Figure 4.13a

16. Prokaryotic cell structures: Gram-positive Cell Walls
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
-teichoic acids-alcohol and phosphate, impart (-) charge, regulate cation mvmt into/out of cell
-periplasm-gel-like fluid betw outer membrane and plasma membrane
-porins-channel proteins that allow nutrients to reach the cell (sugars, proteins/aas, nucleotides)
-penicillin interferes with the peptide cross-bridge formation, weakening cells and making them susceptible to lysis
-Gm(-)—due to less peptidoglycan, more susceptible to mechanical breakage
-strong (-) charge provides barrier to host defenses (phagocytosis and complement, enzymes) and antibiotics

17. 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
Figure 4.13b, c

18. Gram-positive cell walls Gram-negative cell walls
Prokaryotic cell structures: Cell Walls
Gram-positive cell walls
Gram-negative cell walls
Thick peptidoglycan
Teichoic acids
Thin peptidoglycan
No teichoic acids
Outer membrane
Lipopolysaccharide
Porins
-mycolic acid-waxy lipid outside of peptidoglycan that prevents uptake of dyes, including those used in Gram stain, so will normally stain Gm-

19. 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

20. 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)
-mycoplasmas-smallest known bacteria
-archaea-if wall present, does NOT contain peptidoglycan

21. 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
-lysozyme from some eukaryotic cells, also tears, mucus, saliva
-L-forms (Proteus genus) form spontaneously or inrt penicillin or lysozyme—can return to the walled state

22. Structures internal to the cell wall
Prokaryotic cells:
Structures internal to the cell wall

23. 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
-peripheral v. integral prtns—whether or not you have to disrupt the membrane to remove them
Figure 4.14b

24. 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)

25. 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)
-passive diffusion processes-solute moves down concentration gradient until evenly distributed (i.e. equilibrium)

26. 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

27. Prokaryotic cell structures: Plasma Membrane
Three types of osmotic solutions:
Isotonic solution
Hypotonic solution*
Hypertonic solution
[sol]solution = [sol]cell
[sol]solution < [sol]cell
[sol]solution > [sol]cell
-usually medium is hypotonic in relation to cytoplasmic solutes, so when cell wall is disrupted by antibiotics, osmotic lysis
Osmotic lysis
Plasmolysis
[sol]cell = concentration of solute inside the cell
Figure 4.18c-e

28. 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
-active translocation necessary when nutrients are in low concentration
-group translocation, specific to prokaryotes=transported substance is chemically altered during transport so that it is no longer permeable to plasma membrane and cannot exit the cell

29. 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 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

30. Prokaryotic cell structures: Other Internal Structures
Ribosomes: machinery for protein synthesis (translation)
Tens of thousands of ribosomes per cell
-70S=complete bacterial ribosome (S=Svedberg units, refering to relative rate of sedimentation during ultra-high-speed cent.)
-some antibiotics target prokaryotic ribosomes, but do no affect eukaryotic host ribosomes
Complete 70S ribosome

31. Prokaryotic cell structures: Other Internal Structures
Inclusions: Reserve deposits
Type:
Metachromatic granules (volutin)
Polysaccharide granules
Lipid inclusions
Sulfur granules
Carboxysomes
Gas vacuoles
Magnetosomes
Contents:
Phosphate reserves (for ATP generation)
Energy reserves
Ribulose 1,5-diphosphate carboxylase for CO2 fixation
Protein covered cylinders
Iron oxide (destroys H2O2)
-’energy reserves’=substances that can be broken down by the cells in order to generate energy
-gas vacuoles-bouyancy

32. 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
-”resting”=not metabolically active

33. Stained pus from a mixed anaerobic infection

34. Functional Anatomy of Eukaryotic Cells
Figure 4.22

35. Functional Anatomy of Eukaryotic Cells: Flagella and Cilia
Contain cytoplasm, enclosed by plasma membrane
Move in a wavelike motion
Figure 4.23

36. Functional Anatomy of Eukaryotic Cells: Flagella and Cilia
Figure 4.23a, b

37. Functional Anatomy of Eukaryotic Cells: Cell Walls and Glycocalyx
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

38. 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

39. 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)

40. 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)

41. 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

42. 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

43. Endosymbiotic Theory
Theory on evolution of eukaryotic cells’ organelles
Prokaryotes: byo
Eukaryotes: ~2.5 byo
Mitochondria and chloroplasts share properties with prokaryotes
Reproduce independently of cell
Size/shape
Circular DNA
Their ribosomes are 70S