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Functional Anatomy of Prokaryotic and Eukaryotic Cells

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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


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