Comparing Prokaryotic and Eukaryotic Cells

Flashcards comparing prokaryotic and eukaryotic cells.

Prokaryote

Comes from the Greek words for pre-nucleus.

Eukaryote

Comes from the Greek words for true nucleus.

Prokaryote

One circular chromosome, not in a membrane; No histones; No organelles; Bacteria: peptidoglycan cell walls; Archaea: pseudomurein cell walls; Divides by binary fission

Eukaryote

Paired chromosomes, in nuclear membrane; Histones; Organelles; Polysaccharide cell walls, when present; Divides by mitosis

Three basic shapes of bacteria

Bacillus (rod-shaped); Coccus (spherical); Spiral; Vibrio (comma); Spirillum (external flagella); Spirochete (endoflagella); Star-shaped; Rectangular

Arrangement of Bacterial Cells

Pairs: diplococci, diplobacilli; Clusters: staphylococci; Chains: streptococci, streptobacilli; Groups of four: tetrads; Cubelike groups of eight: sarcinae

Glycocalyx

External to the cell wall; Viscous and gelatinous; Made of polysaccharide and/or polypeptide; Capsule: neatly organized and firmly attached; Slime layer: unorganized and loose; Contribute to virulence; Capsules prevent phagocytosis; Extracellular polymeric substance helps form biofilms

Flagella

Filamentous appendages external of the cell; Propel bacteria; Made of protein flagellin; Filament: outermost region; Hook: attaches to the filament; Basal body: consists of rod and pairs of rings; anchors flagellum to the cell wall and membrane

Function of Flagella

Allow bacteria to move toward or away from stimuli (taxis); rotate to run or tumble; proteins are H antigens and distinguish among serovars (e.g., Escherichia coli O157:H7)

Axial Filaments

Also called endoflagella; Found in spirochetes; Anchored at one end of a cell; Rotation causes cell to move like a corkscrew

Fimbriae

Hairlike appendages that allow for attachment

Pili

Involved in motility (gliding and twitching motility); conjugation pili involved in DNA transfer from one cell to another

Cell Wall

Prevents osmotic lysis and protects the cell membrane; Made of peptidoglycan (in bacteria); Contributes to pathogenicity

Peptidoglycan

Polymer of a repeating disaccharide in rows: N-acetylglucosamine (NAG); N-acetylmuramic acid (NAM); Rows are linked by polypeptides

Teichoic acids

Lipoteichoic acid links cell wall to plasma membrane; Wall teichoic acid links the peptidoglycan; Carry a negative charge; Regulate movement of cations; Polysaccharides and teichoic acids provide antigenic specificity

Gram-Negative Cell Walls

Periplasm between the outer membrane and the plasma membrane contains peptidoglycan; Outer membrane made of polysaccharides, lipoproteins, and phospholipids; Protect from phagocytes, complement, and antibiotics; Made of lipopolysaccharide (LPS); O polysaccharide functions as antigen (e.g., E. coli O157:H7); Lipid A is an endotoxin embedded in the top layer; Porins (proteins) form channels through membrane

Gram-Positive Cell Walls

Thick peptidoglycan; Teichoic acids; 2-rings in basal body of flagella; Produce exotoxins; High susceptibility to penicillin; Disrupted by lysozyme

Gram-Negative Cell Walls

Thin peptidoglycan; Outer membrane; Periplasmic space; 4-rings in basal body of flagella; Produce endotoxins and exotoxins; Low susceptibility to penicillin

Gram-Positive Cell Walls and the Gram Stain Mechanism

Alcohol dehydrates peptidoglycan; CV-I crystals do not leave

Gram-Negative Cell Walls and the Gram Stain Mechanism

Alcohol dissolves outer membrane and leaves holes in peptidoglycan; CV-I washes out; cells are colorless; Safranin added to stain cells

Acid-fast cell walls

Like gram-positive cell walls; Mycobacterium; Nocardia; Stain with carbolfuchsin; Waxy lipid (mycolic acid) bound to peptidoglycan

Mycoplasmas

Lack cell walls; Sterols in plasma membrane

Archaea

Wall-less, or walls of pseudomurein (lack NAM and D-amino acids)

Lysozyme

Hydrolyzes bonds in peptidoglycan

Penicillin

Inhibits peptide bridges in peptidoglycan

Protoplast

Wall-less gram-positive cell

Spheroplast

Wall-less gram-negative cell

L forms

Wall-less cells that swell into irregular shapes

Plasma (Cytoplasmic) Membrane

Phospholipid bilayer that encloses the cytoplasm; Peripheral proteins on the membrane surface; Integral and transmembrane proteins penetrate the membrane

Fluid mosaic model

Membrane is as viscous as olive oil; Proteins move freely for various functions; Phospholipids rotate and move laterally; Self-sealing

Functions of the Plasma Membrane

Selective permeability allows the passage of some molecules, but not others; Contain enzymes for ATP production; Some membranes have photosynthetic pigments on foldings called chromatophores

Damage to the Plasma Membrane

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

Passive processes

Substances move from high concentration to low concentration; no energy expended

Active processes

Substances move from low concentration to high concentration; energy expended

Simple diffusion

Movement of a solute from an area of high concentration to an area of low concentration; Continues until molecules reach equilibrium

Facilitated diffusion

Solute combines with a transporter protein in the membrane; Transports ions and larger molecules across a membrane with the concentration gradient

Osmosis

The movement of water across a selectively permeable membrane from an area of high water to an area of lower water concentration; Through lipid layer; Aquaporins (water channels)

Isotonic solution

Solute concentrations equal inside and outside of cell; water is at equilibrium

Hypotonic solution

Solute concentration is lower outside than inside the cell; water moves into cell

Hypertonic solution

Solute concentration is higher outside of cell than inside; water moves out of cell

Active transport

Requires a transporter protein and ATP; goes against gradient

Group translocation

Requires a transporter protein and phosphoenolpyruvic acid (PEP); substance is altered as it crosses the membrane

Cytoplasm

Eighty percent water plus proteins, carbohydrates, lipids, and ions; Cytoskeleton

Bacterial chromosome (nucleoid)

Circular thread of DNA that contains the cell's genetic information

Plasmids

Extrachromosomal genetic elements; carry non-crucial genes (e.g., antibiotic resistance, production of toxins)

Ribosomes

Sites of protein synthesis; Made of protein and ribosomal RNA; 70S (Prokaryotes); 50S + 30S; 80S (Eukaryotes); 60S + 40S subunits

Metachromatic granules (volutin)

Phosphate reserves

Polysaccharide granules

Energy reserves

Gas vacuoles

Protein-covered cylinders that maintain buoyancy

Magnetosomes

Iron oxide inclusions; destroy H2O2

Endospores

Resting cells; produced when nutrients are depleted; resistant to desiccation, heat, chemicals, and radiation; produced by Bacillus and Clostridium

Sporulation

Endospore formation

Germination

Endospore returns to vegetative state

Flagella

Long projections; few in number

Cilia

Short projections; numerous

Flagella and Cilia

Consist of microtubules made of the protein tubulin; Microtubules are organized as nine pairs in a ring, plus two microtubules in the center (9 + 2 array); Allow flagella to move in a wavelike manner

Cell wall

Found in plants, algae, and fungi; Made of carbohydrates cellulose - plants, chitin - fungi, glucan and mannan - yeasts

Glycocalyx

Found in animal cells; Carbohydrates bonded to proteins and lipids in the plasma membrane

Plasma (Cytoplasmic) Membrane

Similar in structure to prokaryotic cell membranes; Phospholipid bilayer; Integral and peripheral proteins; Sterols—complex lipids; Carbohydrates—for attachment and cell-to-cell recognition

Plasma (Cytoplasmic) Membrane Function

Selective permeability; Simple diffusion, facilitated diffusion, osmosis, active transport

Phagocytosis

Pseudopods extend and engulf particles

Pinocytosis

Membrane folds inward, bringing in fluid and dissolved substances

Cytoplasm

Substance inside the plasma and outside the nucleus

Cytosol

Fluid portion of cytoplasm

Cytoskeleton

Made of microfilaments and intermediate filaments; gives shape and support

Cytoplasmic streaming

Movement of the cytoplasm throughout a cell

80S Ribosomes

Consists of the large 60S subunit and the small 40S subunit

70S

In chloroplasts and mitochondria

Nucleus

Double membrane structure (nuclear envelope) that contains the cell's DNA; DNA is complexed with histone proteins to form chromatin; During mitosis and meiosis, chromatin condenses into chromosomes

Rough ER

Studded with ribosomes; sites of protein synthesis

Smooth ER

No ribosomes; synthesizes cell membranes, fats, and hormones

Golgi Complex

Modifies proteins from the ER; Transports modified proteins via secretory vesicles to the plasma membrane

Mitochondria

Contain inner folds (cristae) and fluid (matrix); Involved in cellular respiration (ATP production)

Lysosomes

Contain digestive enzymes

Vacuoles

Bring food into cells; provide shape and storage

Peroxisomes

Oxidize fatty acids; destroy H2O2

Centrosomes

Networks of protein fibers and centrioles; Form the mitotic spindle; critical role in cell division

Chloroplasts

Locations of photosynthesis; Contain flattened membranes (thylakoids) that contain chlorophyll

Endosymbiotic theory

Larger bacterial cells engulfed smaller bacterial cells, developing the first eukaryotes; Ingested photosynthetic bacteria became chloroplasts; Ingested aerobic bacteria became mitochondria