Prokaryotic and Eukaryotic Cells

                 Prokaryote comes from the Greek words for prenucleus.

                 Eukaryote comes from the Greek words for true nucleus.

 

Prokaryote

                 One circular chromosome, not in a membrane

                 No histones

                 Binary fission

                 No organelles except ribosomes

                 Peptidoglycan cell walls if Bacteria

                 Pseudomurein cell walls if Archaea

Eukaryote

                 Paired chromosomes, in a nuclear membrane

                 Histones

                 Mitotic spindle

                 Organelles

                 Polysaccharide cell walls

 

Prokaryotic Cells: Shapes

                 Average size: 0.2 –1.0 m 2 – 8 m

                 Most bacteria are monomorphic

                 A few are pleomorphic

 

                 Bacillus (rod-shaped)

                 Coccus (spherical)

                 Spiral

             Spirillum                                      

             Vibrio                                                               

             Spirochete                                                    

 

Cell Arrangements

                 Pairs: Diplococci, diplobacilli

                 Clusters: Staphylococci

                 Chains: Streptococci, streptobacilli

 

The Structure of a Prokaryotic Cell

 

Glycocalyx

                 Outside cell wall

                 Usually sticky

                 Capsule: a neatly organized glycocalyx

                 Slime layer: unorganized and loose glycocalyx

                 Extracellular polysaccharide allows cell to attach

                 Capsules prevent phagocytosis

 

Flagella

                 Outside cell wall

                 Made of chains of flagellin

                 Attached to a protein hook

                 Anchored to the wall and membrane by the basal body

 

Motile Cells

                 Rotate flagella to run or tumble

                 Move toward or away from stimuli (taxis)

                 Flagella proteins are H antigens
(e.g., E. coli O157:H7)

 

Axial Filaments

                 Also called endoflagella

                 In spirochetes

                 Anchored at one end
of a cell

                 Rotation causes cell
to move

 

Fimbriae and Pili

                 Fimbriae allow attachment

                 Pili

             Facilitate transfer of DNA from one cell to another

             Gliding motility

             Twitching motility

 

The Cell Wall

                 Prevents osmotic lysis

                 Made of peptidoglycan (in bacteria)

 

Peptidoglycan

                 Polymer of disaccharide:

             N-acetylglucosamine (NAG)

             N-acetylmuramic acid (NAM)

 

 

 

Peptidoglycan in Gram-Positive Bacteria

                 Linked by polypeptides

 

Gram-positive Cell Wall

                 Thick peptidoglycan

                 Teichoic acids

 

Gram-negative Cell Wall

                 Thin peptidoglycan

                 Outer membrane

                 Periplasmic space

 

Gram-positive Cell Wall

                 Teichoic acids

             Lipoteichoic acid links to plasma membrane

             Wall teichoic acid links to peptidoglycan

                 May regulate movement of cations

                 Polysaccharides provide antigenic variation

 

Gram-Negative Outer Membrane

                 Lipopolysaccharides, lipoproteins, phospholipids

                 Forms the periplasm between the outer membrane and the plasma membrane

                 Protection from phagocytes, complement, and antibiotics

                 O polysaccharide antigen, e.g., E. coli O157:H7

                 Lipid A is an endotoxin

                 Porins (proteins) form channels through membrane

 

The Gram Stain Mechanism

                 Crystal violet-iodine crystals form in cell

                 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

 

Gram-Positive Cell Wall

                 2-ring basal body

                 Disrupted by lysozyme

                 Penicillin sensitive

 

Gram-Negative Cell Wall

                 4-ring basal body

                 Endotoxins

                 Tetracycline sensitive

 

Atypical Cell Walls

                 Acid-fast cell walls

             Like gram-positive cell walls

             Have waxy lipid (mycolic acid) bound to peptidoglycan

             Carbolfuchsin stains through waxy layer & wall

             Mycobacterium

             Nocardia

                 Mycoplasmas

             Lack cell walls

             Sterols in plasma membrane for protection

                 Archaea

             Wall-less or

             Walls of pseudomurein (lack NAM and D-amino acids)

 

Damage to the Cell Wall

                 Lysozyme digests disaccharide in peptidoglycan

                 Penicillin inhibits peptide bridges in peptidoglycan

                 Protoplast is a wall-less cell

                 Spheroplast is a wall-less gram-positive cell

             Protoplasts and spheroplasts are susceptible to osmotic lysis

                 L forms are wall-less cells that swell into irregular shapes

 

The Plasma Membrane

                 Phospholipid bilayer

                 Peripheral proteins

                 Integral proteins

                 Transmembrane

                 Proteins

 

Fluid Mosaic Model

                 Membrane is as viscous as olive oil

                 Proteins move to function

                 Phospholipids rotate
and move laterally

 

The Plasma Membrane

                 Selective permeability allows passage of some molecules

                 Enzymes for ATP production

                 Photosynthetic pigments on foldings called chromatophores or thylakoids

 

Chromatophores

                 In-foldings of the plasma membrane

 

The Plasma Membrane

                 Damage to the membrane by alcohols, quaternary ammonium (detergents), and polymyxin antibiotics causes leakage of cell contents

 

Movement of Materials across Membranes

                 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 in the membrane

                 Osmosis: The movement of water across a selectively permeable membrane from an area of high water to an area of lower water concentration

                 Osmotic pressure: The pressure needed to stop the movement of water across the membrane

 

Movement of Materials across Membranes

                 Through lipid layer

                 Aquaporins (water channels)

 

The Principle of Osmosis

                 Understand this concept!

 

Movement of Materials across Membranes

                 Active transport: Requires a transporter protein and ATP

                 Group translocation: Requires a transporter protein and PEP

 

Cytoplasm

                 The substance inside the plasma membrane

 

The Nucleoid

                 Bacterial chromosome

 

The Prokaryotic Ribosome

                 Protein synthesis

                 70S

             50S + 30S subunits

 

Inclusions

                 Metachromatic granules (volutin)        - Phosphate reserves

                 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)   

 

Endospores

                 Resting cells

                 Resistant to desiccation, heat, chemicals

                 Bacillus, Clostridium

                 Sporulation: Endospore formation

                 Germination: Return to veg. state

 

The Eukaryotic Cell

 

Flagella and Cilia

                 Microtubules

                 Tubulin

                 9 pairs + 2 array                                    

 

The Cell Wall and Glycocalyx

                 Cell wall

             Plants, algae, fungi

             Carbohydrates

                 Cellulose, chitin, glucan, mannan

                 Glycocalyx

             Carbohydrates extending from animal plasma membrane

             Bonded to proteins and lipids in membrane

 

The Plasma Membrane

                 Phospholipid bilayer

                 Peripheral proteins

                 Integral proteins

                 Transmembrane proteins

                 Sterols

                 Glycocalyx carbohydrates

 

The Plasma Membrane

                 Selective permeability allows passage of some molecules

                 Simple diffusion

                 Facilitative diffusion

                 Osmosis

                 Active transport

                 Endocytosis

             Phagocytosis: Pseudopods extend and engulf particles

             Pinocytosis: Membrane folds inward, bringing in fluid and dissolved substances

 

Cytoplasm

                 Cytoplasm membrane: Substance inside plasma and outside nucleus

                 Cytosol: Fluid portion of cytoplasm

                 Cytoskeleton: Microfilaments, intermediate filaments, microtubules

                 Cytoplasmic streaming: Movement of cytoplasm throughout cells

 

Ribosomes

                 Protein synthesis

                 80S

             Membrane-bound: Attached to ER

             Free: In cytoplasm

                 70S

             In chloroplasts and mitochondria

 

Organelles

                 Nucleus: Contains chromosomes

                 ER: Transport network

                 Golgi complex: Membrane formation and secretion

                 Lysosome: Digestive enzymes

                 Vacuole: Brings food into cells and provides support

                 Mitochondrion: Cellular respiration

                 Chloroplast: Photosynthesis

                 Peroxisome: Oxidation of fatty acids; destroys H2O2

                 Centrosome: Consists of protein fibers and centrioles

 

Endosymbiotic Theory

                 Know this concept in general terms