Functional Anatomy of Prokaryotic and Eukaryotic Cells Chapter 4 Functional Anatomy of Prokaryotic and Eukaryotic Cells

Prokaryotic Cells Comparing Prokaryotic and Eukaryotic Cells Learning objective: compare and contrast overall cell structure of prokaryotes and eukaryotes. Comparing Prokaryotic and Eukaryotic Cells Prokaryote comes from the Greek words for prenucleus. Eukaryote comes from the Greek words for true nucleus.

Prokaryote Eukaryote Cell membrane Cytoplasm One circular chromosome, not in a membrane No histones No organelles Peptidoglycan cell walls Binary fission Cell membrane Cytoplasm Paired chromosomes, in nuclear membrane Histones Organelles Polysaccharide cell walls Mitotic spindle

Average size: 0.2 -1.0 µm  2 - 8 µm (1 x 10-6 m) Learning objective: Identify the three basic shapes of bacteria. Average size: 0.2 -1.0 µm  2 - 8 µm (1 x 10-6 m) Are unicellular and most multiply by binary fission Basic shapes: COCCUS BACILLUS SPIRAL

Arrangements Pairs: diplococci, diplobacilli Clusters: staphylococci Chains: streptococci, streptobacilli

Arrangements of cocci: Can be determined by division of planes.

Arrangements of bacilli:

Arrangements of spiral bacteria:

Double-stranded helix formed by Bacillus subtilis. Bacillus cells often remain attached to each other, forming extended chains.

Unusual shapes (Prokaryotes) Star-shaped Stella Square Haloarcula (halophilic archaea – salt-loving) Most bacteria are monomorphic (single shape) A few are pleomorphic (many shapes) Figure 4.5

Learning objective: Describe the structure and function of the glycocalyx, flagella, axial filaments, fimbriae, and pili. Prokaryote cell

Glycocalyx Outside cell wall Usually sticky A capsule is neatly organized A slime layer is unorganized & loose glycocalyx Extracellular polysaccharide (EPS) allows cell to attach Capsules prevent phagocytosis Protects against dehydration or loss of nutrients. Figure 4.6a, b

Flagella Long filamentous appendages of a filament, hook, and basal body Outside cell wall Made of chains of flagellin Attached to a protein hook Anchored to the wall and membrane by the basal body Figure 4.8

Flagella Arrangement Four arrangements of flagella: Figure 4.7

Motile Cells Rotate flagella to run or tumble Move toward or away from stimuli (positive and negative taxis) Flagella H proteins are antigens (e.g., E. coli O157:H7)

Motile Cells A Proteus cell swarming may have 1000+ peritrichous flagella. (from all sides) Figure 4.9

Axial Filaments (endoflagellum) Endoflagella In spirochetes Anchored at one end of a cell Rotation causes cell to move Figure 4.10a

Fimbriae and Pili Are short, thin appendages Fimbriae of this E. Coli cell allow attachment (velcro). Cell is beginning to divide. Pili are used to transfer DNA from one cell to another Figure 4.11

Learning objectives: Compare/contrast cell walls of gram-positive bacteria, gram-negative bacteria, archaea, and mycoplasmas. Differentiate between protoplast, spheroplast, and L form. Cell Wall Prevents osmotic lysis (protects against changes in water pressure) Made of peptidoglycan (in bacteria = NAG+NAM+amino acids) – penicillin interferes with production of peptidoglycan Contributes to disease capability and site of action of some antibiotics. Figure 4.6a, b

Peptidoglycan (murein) Polymer of disaccharide N-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM) Linked by polypeptides The small arrows denote where penicillin interferes with linkage of peptidoglycan rows. Figure 4.13a

Gram positive vs. gram negative cell walls Figure 4.13b, c

Gram-positive cell walls Gram-negative cell walls Thick peptidoglycan Teichoic acids (alcohol+phosphate) In acid-fast cells, contains mycolic acid (waxy lipid) – allows them to be grouped into medically significant types. Thin peptidoglycan (subject to mechanical breakage) No teichoic acids Outer membrane: Evades phagocytosis Barrier to certain anti-biotics

Gram-Positive cell walls Teichoic acids: Lipoteichoic acid links to plasma membrane Wall teichoic acid links to peptidoglycan May regulate movement of cations (+ charge) Polysaccharides provide antigenic variation (identification) Figure 4.13b

Gram-Negative Outer Membrane Lipopolysaccharides, lipoproteins, phospholipids. Forms the periplasm between the outer membrane and the plasma membrane. Protection from phagocytes, complement (30+ liver proteins that protect host), antibiotics. O polysaccharide antigen, e.g., E. coli O157:H7. Lipid A is an endotoxin. Porins (proteins) form channels through membrane to pass other molecules

Gram-Negative Outer Membrane Figure 4.13c

Gram Stain Mechanism Crystal violet-iodine (CV-I) crystals form in cell combining with peptidoglycan Gram-positive Alcohol dehydrates peptidoglycan CV-I crystals do not leave Gram-negative Alcohol dissolves outer membrane and leaves holes in peptidoglycan CV-I washes out

Atypical Cell Walls Mycoplasmas (Genus) Lack cell walls Sterols in plasma membrane Archaea Wall-less, or Walls of pseudomurein (lack NAM and D amino acids, peptidoglycan)

Damage to Cell Walls Lysozyme digests disaccharide in peptidoglycan (gram+ cell walls destroyed, gram- damaged, resulting in spheroplast). Spheroplast is a wall-less Gram-positive cell. Penicillin inhibits peptide bridges in peptidoglycan. Protoplast is a wall-less cell. L forms are wall-less cells that swell into irregular shapes (gram+ and -). Protoplasts and spheroplasts are susceptible to osmotic lysis.

Plasma (cytoplasmic) Membrane Learning objectives: Describe the structure, chemistry, and functions of prokaryotic plasma membrane. Define simple diffusion, facilitated diffusion, osmosis, active transport, and group translocation. Figure 4.14a

Plasma Membrane – Fluid Mosaic Model Selectively permeable Phospholipid bilayer Peripheral proteins Integral proteins Transmembrane proteins Figure 4.14b

Fluid Mosaic Model Membrane is as viscous as olive oil. Proteins move to function Phospholipids rotate and move laterally Figure 4.14b

Plasma Membrane Carry enzymes for metabolic reactions: nutrient breakdown, energy production, photosynthesis Selective permeability allows passage of some molecules Enzymes for ATP production Photosynthetic pigments on foldings called chromatophores or thylakoids Damage to the membrane by alcohols, quaternary ammonium (detergents) and polymyxin antibiotics causes leakage of cell contents.

Movement Across Membranes High to low concentration: Movement may be passive (no energy expenditure – diffusion or facilitated diffusion): Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration. (ions move until equilibrium reached) Facilitative diffusion: Solute combines with a transporter protein in the membrane.

Movement Across Membranes Figure 4.17

Movement Across Membranes Osmosis (always involves water): Movement of water across a selectively permeable membrane from an area of high water concentration to an area of lower water. Osmotic pressure The pressure needed to stop the movement of water across the membrane. Figure 4.18a

Osmosis Figure 4.18c-e

Movement Across Membranes Low to high concentration (against gradient) – cell must expend energy: Active transport of substances requires a transporter protein and ATP. Group translocation of substances requires a transporter protein and PEP. (phospheonolpyruvic acid)

Cytoplasm Cytoplasm is the fluid substance inside the plasma membrane (water, inorganic and organic molecules, DNA, ribosomes, and inclusions) Figure 4.6a, b

Nuclear Area Learning objectives: Identify functions of the nuclear area, ribosomes, and inclusions. Nuclear area (nucleoid) – contains single long, continuous, double-stranded DNA called bacterial chromosome. Bacteria can contain plasmids – circular DNA Figure 4.6a, b

Ribosomes = rRNA + proteins Sites of protein synthesis (rRNA) – free floating, not tied to endoplasmic reticulum as in eukaryotes. Figure 4.6a

Ribosomes The letter S refers to Svedberg units = relative rate of sedimentation. Because of differences in prokaryotic and eukaryotic ribosomes, the microbe can be killed by antibiotics while eukaryotic host cell is unaffected. Figure 4.19

Inclusions Metachromatic granules (volutin) Phosphate reserves FUNCTION Metachromatic granules (volutin) Polysaccharide granules Lipid inclusions Sulfur granules Carboxysomes Gas vacuoles Magnetosomes Phosphate reserves Energy reserves Ribulose 1,5-diphosphate carboxylase for CO2 fixation Protein covered cylinders Iron oxide (destroys H2O2)

Iron-oxide inclusions in some gram-negative bacteria that act like magnets.

Endospores Resting cells formed for survival Learning objective: Describe the functions of endospores, sporulation, and endospore germination. Resting cells formed for survival Sporulation: Endospore formation Resistant to desiccation, heat, chemicals Bacillus, Clostridium Germination: Return to vegetative state

Endospores tend to form under conditions of stress.

Eukaryotic Cells Comparing Prokaryotic and Eukaryotic Cells Prokaryote comes from the Greek words for prenucleus. Eukaryote comes from the Greek words for true nucleus.

Eukaryotic Flagella and Cilia Prokaryotic flagella rotate, eukaryotic flagella wave Euglena (evolutionary building block)

Flagella and Cilia Flagella are few and long (motility), cilia are numerous and short (motility and move substances along cell surface) Microtubules Tubulin 9 pairs + 2 arrangements Figure 4.23c

Cell Wall and Glycocalyx Learning objective: Compare and contrast prokaryotic and eukaryotic cell walls and glycocalyxes. Cell wall Plants, algae, some fungi contain cellulose Carbohydrates Cellulose, chitin (fungal), glucan & mannan (yeast) Glycocalyx surround animal cells (strength, attachment to other cells) Carbohydrates extending from animal plasma membrane Bonded to proteins and lipids in membrane

Plasma Membrane Phospholipid bilayer in both p. and e. cells Learning objective: Compare and contrast prokaryotic and eukaryotic plasma membranes. Phospholipid bilayer in both p. and e. cells Peripheral proteins Integral proteins Transmembrane proteins Sterols Glycocalyx carbohydrates not found in p. cells except Mycoplasma bacteria

Plasma Membrane Selective permeability allows passage of some molecules Simple diffusion Facilitative diffusion Osmosis Active transport Endocytosis Phagocytosis: Pseudopods extend and engulf particles (solids) Pinocytosis: Membrane folds inward bringing in fluid and dissolved substances (liquids)

Eukaryotic Cell Cytoplasm Substance inside plasma membrane and outside nucleus Cytosol Fluid portion of cytoplasm Cytoskeleton Microfilaments, intermediate filaments, microtubules Cytoplasmic streaming Movement of cytoplasm throughout cells Learning objectives: Define organelle. Describe the functions of the nucleus, endoplasmic reticulum, ribosomes, Golgi complex, lysosomes, vacuoles, mitochondria, chloroplasts, peroxisomes, and centrosomes.

Organelles Specialized membrane-bound structure in cytoplasm: Nucleus Contains chromosomes (DNA) ER Transport network, ribosomes Golgi complex Membrane formation and protein secretion Lysosome Digestive enzymes Vacuole Brings food into cells and provides support Mitochondrion Cellular respiration (ATP) Chloroplast Photosynthesis (70S ribosomes) Peroxisome Oxidation of fatty acids; destroys H2O2

Eukaryotic Cell Not membrane-bound: Ribosome Protein synthesis (translation) Centrosome Consists of protein fibers and centrioles Centriole Mitotic spindle formation

Eukaryotic Nucleus Figure 4.24

Endoplasmic Reticulum Rough ER contains ribosomes – site of protein translation Smooth ER performs various functions: Synthesizes phospholipids, fats, steroids In liver: glucose release and detoxify toxins Creates vesicles Figure 4.25

Ribosomes 80S Membrane-bound Attached to ER Free In cytoplasm 70S In chloroplasts and mitochondria

Golgi Complex Golgi complex modifies, sorts, and packages proteins received from the ER; discharges proteins via exocytosis; replaces portions of the plasma membrane; and forms lysosomes (digestive enzymes). Figure 4.26

Lysosomes (digestive enzymes) Figure 4.22b

Vacuoles (storage of toxins, food, water) Figure 4.22b

Mitochondrion (furnace of the cell) Site of the Krebs Cycle, which produces the energy currency of the cell - ATP Figure 4.27

Chloroplast Structure similar to mitochondria – the reverse side of respiration: C6H12O6 + O2 = H2O + CO2 + ATP Photosynthesis: H2O + CO2 + sun = C6H12O6 + O2 Figure 4.28

Endosymbiotic Theory Learning objective: Discuss evidence that supports the endosymbiotic theory of eukaryotic evolution. Mitochondria and chloroplasts resemble bacteria in size and shape as do their ribosomes These organelles contain circular DNA like prokaryotes and can reproduce apart from their host cell Figure 10.2