Chapter 4: Functional Anatomy of Prokaryotic & Eukayotic Cellss

Key Functions fo Cells

• A boundary that keeps the cellular contents separate from the external environment but allows for the transfer of some substances into and out of the cell. 

• Replication of DNA 

• Synthesis of cellular components 

• The ability to obtain energy through metabolic processes 

Prokaryote

• One circular chromosome, not in a membrane 

• No histones 

• No organelles 

• Bacteria: peptidoglycan cell walls 

• Archaea: pseudomurein cell walls 

• Divides by binary fission 

  • Smaller (1-10 mm) 

    • Simpler in structure 

  • DNA concentrated in nucleoid region, which is not separated from rest of cell by a membrane 

  • DNA is found as a single, circular chromosomes 

    • Lacks most organelles 

    • Rigid cell wall found outside outer wrapper (cell membrane) 

Eukaryote

• Paired chromosomes, in nuclear membrane 

• Histones 

• Organelles  

• Polysaccharide cell walls, when present  

• Divides by mitosis 

  • Larger (10-100 mm) 

    • More complex structure 

  • Nucleus enclosed by membrane  

    • Contains many types of organelles 

    • DNA found in several linear chromosomes 

    • Rigid cell wall found only surrounding plant and fungal cells 

The Size, Shape and Arrangement of Bacterial Cells 

• Average size: 0.2 to 2.0 Mm diameter x 2 to 8 Mm length 

• Most bacteria are monomorphic (single shaped) 

• A few are pleomorphic (many shapes) 

Spiral

• Vibrio 

• Spirillum 

• Spirochete 

Cocci

• Clusters: staphylococci 

• Chains: streptococci 

• Group of four: tetrads 

• Cubelike groups of eight: sarcinae 

Bacilli

• Pairs: diplococci, diplobacilli 

• Chains: streptobacilli 

• Groups of four: tetrads 

• Cubelike: groups of eight: sarcinae 

Prokaryotic Cell Structure

It is composed of

• Glycocalyx

  • External to the cell wall 

• Viscous and gelatinous 

• Made of polysaccharide and/or polypeptide 

  • Capsule

  • Slime Layer

Glycocalyx of Prokaryotic Cell

• Term to describe substances that surround bacterial cells 

Capsule

• If substance is organized and firmly attached to cell wall 

• Function

  • Prevents drying out or desiccation 

  • Allows bacteria to adhere to various surfaces 

    • Streptococcus mutants – enamel on teeth to cause dental carries 

    • Klebsiella pneumoniae – attaches to respiratory tract 

    • Streptococcus pneumoniae – causes pneumonia  

  • Contribute to Virulence of bacteria by preventing phagocytosis by WBC’s 

Slime Layer

• If substance is unorganized and loosely attached to cell wall 

Flagella Stucture

• (Singular flagellum) are cellular appendages that consist of three parts:

  • Made of protein flagellin 

  • A filament that rotates for movement 

  • A hook where the filament attaches 

  • A basal body that anchors the hook to the cell 

    • The arrangement of the hook/basal body articulation allows the hook with its filament to rotate 360 degrees. 

Flagellar Arrangment

• Atrichous: no flagella 

• Peritrichous: many around 

• Monotrichous: only one 

• Lophotrichous: multiple at one end 

• Amphitrichous: at both ends 

Axial Filaments

• Are modified flagella that occur in spirochetes 

• Flexible spirals 

Flagella Function

• It allow bacteria to move toward or away from stimuli (taxis) 

• It rotate to “run” or “tumble” 

• The proteins are H antigens and distinguish among serovars  

Chemotaxis

• Directed movement 

• In response to a chemical  

• Through a specific chemoreceptor

• Movement to a chemical = chemoattractant (ex: sugar & amino acids) 

• Movement away from chemical = chemorepellent (toxic substances) 

Archaella

• The motility structure 

• Made of glycoproteins acrihellins 

• Anchored to the cell 

• It (singular: archlaellum) rotate like flagella 

Fimbriae of Prokaryotic cell

• Hairlike appendages that allow for attachment  

• a few-hundreds

• Main function is attachment

Pili

• Involved in motility (gliding and twitching motility)  

• Conjugation pili involved in DNA transfer from one cell to another 

• typically 1 or 2 only and longer

Peptidogylcan

• Polymer of a repeating
  disaccharide in rows:

  • N-acetylglucosamine (NAG)

  • N-acetylmuramic acid
    (NAM)

  • Rows are linked by polypeptides

Gram-Positive Cell Walls

• 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 

• High susceptibility to penicillin, Disrupted by lysozyme, and Produce exotoxins

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.coli) 

  • Lipid A is an endotoxin embedded in the top layer 

• Porins (proteins) form channels through membrane 

Lipopilysaccharide

• Lipid A 

  • The culprit for fever (endotoxin) 

  • Highly conserved 

• Core sugar 

  • Conserved 

• Sugar chain of varying length (O-antigen, “ohne Hauch”, used for typing)

Cell Walls and the Gram Stain Mechanism 

• Crystal violet-iodine crystals form inside 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; cells are colorless 

  • Safranin added to stain cells 

Acid-fast cell walls 

• Like gram-positive cell walls 

• Waxy lipid (mycolic acid) bound to peptidoglycan 

• Mycobacterium 

• Nocardia 

• Stain with carbolfuchsin 

Atypical Cell Walls

• Acid-fast cell walls

• Mycoplasmas 

  • Lack cell walls  

  • Sterols in plasma membrane 

• Archaea 

  • Wall-less, or 

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

 

Damage to the Cell Wall

• Lysozyme hydrolyzes bonds in peptidoglycan 

• Penicillin inhibits peptide bridges in peptidoglycan 

• Protoplast is a wall-less gram-positive cell 

• Spheroplast is a wall-less gram-negative cell  

  • Protoplast and spheroplasts are susceptible to osmotic lysis 

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

The Plasma (Cytoplasmic) Membrane 

• Phospholipid bilayer that encloses the cytoplasm 

• Peripheral proteins on the membrane surface 

• Integral and transmembrane proteins penetrate the membrane

Prokaryotic Cell Membrane 

• Also called inner membrane (no nucleus) 

• Double phospholipid layer with proteins (often glycoproteins) 

• Lipids differ from eukaryotic cell membranes 

  • No sterols (exception: Mycoplasma steal sterols from host) 

• Protection toward outside 

• Containment of cytoplasmic material 

• Selective uptake of molecules 

• Site of energy production in many species 

• Target of some antibiotic (ex: polymyxin B) and disinfectants (ex: alcohols)  

Structure of Prokaryotic Plasma Membrane

• Fluid mosaic model 

  • Membrane is as viscous as olive oil 

  • Proteins move freely for various functions 

  • Phospholipids rotate and move laterally 

  • Self-sealing 

• It selective permeability allows the passage of some molecuels, but not others 

• Contain enzymes for ATP production 

• Some membranes have photosynthetic pigments on folding called chromatophores 

Function of Prokaryotic Cell Membrane

• Selective barrier (selectively permeable) 

• ETS is located here 

• Enzymes for cell wall synthesis 

• If photosynthesis, enzymes are located on membranous structures called thylakoids 

• Mesosomes – invagination of cell membrane to DNA 

• Secretes exoenzymes 

  • Amylases 

  • Lipases 

  • peptidases 

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 

Osmosis

• Is the diffusion of water across a semi-permeable membrane. Environment surrounding cells may contain amounts of dissolved substances (solutes) that are 

Isotonic

• Equal concentration of a solute inside and outside of cell 

Hypertonic

• A higher concentration of solute

• Cell shrinks, water leaves out of cell

Hypotonic

• A lower concentration of solute.

• Water will always move toward a hypertonic environment

• Cell swells, water moves into the cell

Prokaryotic Cytoplasm 

• 80% water 

• Contains primarily proteins (enzymes), carbohydrates, lipids, inorganic ions, many low molecular weight compounds 

• Thick, aqueous semitransparent, and elastic 

Prokaryotic Nucleoid 

• Bacterial Chromosome 

• Contains the essential genetic information 

• Circular double-stranded DNA stabilized by histone-like proteins (not by histones) 

• No nuclear envelope!! 

• Cell division by binary fission 

Prokaryotic Plasmids 

• Small circular double-stranded DNA that can multiply independently  

• Not essential under normal physiological conditions 

• Contain additional genes often involved in pathogenesis 

  • Virulence factors 

  • Antibiotic resistance 

  • Toxic metal resistance 

• Copy number varies (a few hundreds) 

  • Can be exploited for recombinant proteins production 

Prokaryotic Ribosomes

• 70S ribosomes (30S + 50S subunit) (they lose proteins mass) 

  • S = Svedberg unit (sedimentation rate upon centrifugation) 

  • Smaller than eukaryotic ribosome 

  • Sediment differently 

• Consist of proteins and ribosomal RNA 

• Site of protein synthesis 

• Contain 16S rRNA on 30S subunit 

• 16S = Important for classification and identification

Selective Toxicity 

• Some antibiotics are aimed at the 70S ribosomes of bacterial cells 

• Streptomycin, Neomycin, Erythromycin, and Tetracycline work by inhibiting protein synthesis by disrupting the 70S ribosome 

Inclusions

• Metachromatic granules (volutin) - phosphate reserves 

• Polysaccharide granules – energy reserves 

• Lipid inclusions – energy reserves 

• Sulfur granules – energy reserves 

• Carboxysomes – RuBis-CO enzyme (most abundant cell) for CO2 fixation during photosynthesis 

• Gas vacuoles – protein covered cylinders that maintain buoyancy (floating, bacteria cells)  

• Magnetosomes – iron oxide inclusions; destroy H2O2 

Bacterial Endospores

• Sporulation is a complex process 

• Triggered under unfavorable conditions (no water or nutrients) 

• Very low water content 

• Spore is multilayered  

• Resistance through spore coat (protein layer) 

• Can survive thousands of years 

• Germination is triggered under favorable conditions 

• Clostridium sp., Bacillus sp. 

 

Endospores

• formed under periods of environmental stress

• Only found in Gram (+) Bacteria 

• Bacillus (aerobic – needs oxygen) 

  • Bacillus cereus 

  • Bacillus anthracis 

• Clostridium (anaerobic – no oxygen) 

  • Clostridium tetani (norovirus tetanus – lock jaw syndrome) 

  • Clostridium botulinum (caused by canned food, no oxygen) (Botox is botulinum) 

  • Clostridium perfringens (caused gangrene = no oxygen no blood flow)  

Flagella in Eukaryotic Cells

• Projections used for locomotion or moving substances along the cell surface 

• It is a long projections; few in number 

• Cilia – short projections; numerous 

• Both consist of microtubules made of the protein tubulin 

• Microtubules are organized as 9 pairs in a ring, plus 2 microtubules in the center  

• Allow flagella to move in a wavelike manner 

Cell Wall of Eukaryotic Cells

• Found in plants, algae, and fungi 

• Made of carbohydrates (cellulose = plants, chitin = fungi, glucan and mannan = yeasts) 

Glycocalyx

• Carbohydrates bonded to proteins (glycoprotein) and lipids (glycolipid) in the plasma membrane 

• Found in animal cells 

Plasma (Cytoplasmic) Membrane of Eukaryotic Cells

• Similar in structure to prokaryotic cell membranes 

  • Phospholipid bilayer 

  • Integral and peripheral proteins 

• Differences in structure 

  • Sterols – complex lipids 

  • Carbohydrates – for attachments and cell to cell recognition 

• Similar in function to prokaryotic cell membranes 

  • Selective permeability 

  • Simple diffusion, faciliated diffusion, osmosis, active transport 

• Differences in function 

  • Endocytosis – phagocytosis and pinocytosis  

  • Phagocytosis: pseudopods extend and engulf particles (brings in cells) 

  • Pinocytosis: membrane folds inward, bringing in fluid and dissolved substance (brings in molecules) 

 

Eukaryotic Cell Cytoplams

• Substance inside the plasma and outside the nucleus 

• Cytosol: fluid portion 

• Cytoskeleton: made of microfilaments and intermediate filaments; give shape and support 

• Cytoplasmic streaming: movement of the cytoplasm throughout a cell 

Ribosomes of Eukaryotuc Cell

• Sites of protein synthesis 

• 80S 

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

  • Membrane-bound: attached to endoplasmic reticulum 

  • Free: in cytoplasm 

• 70S 

  • In chloroplasts and mitochodria 

Eukaryotic Cell Nucleus

• Double membrane structure (nuclear envelop) that contains the cell’s DNA 

• DNA is complexed with histone proteins to form chromatin 

• During mitosis and meiosis, chromatin condenses into chromosomes 

Endoplasmic Reticulum of Eukaryotic Cell

• Folded transport network 

• Rough ER: studded with ribosomes; site of proteins synthesis 

• Smooth ER: no ribosomes; synthesizes cell membranes, fats, and hormones 

Golgi Complex of Eukaryotic Cell

• Transport organelle 

• Modifies protein from the ER 

• Transports modified proteins via secretory vesicles to the plasma membrane 

Lysomes

• Vesicles formed in the Golgi complex 

• Contain digestive enzymes 

Vacuoles 

• Cavities in the cell formed from the Golgi complex 

• Bring food into cells; provide shape and storage 

Mitochondria of Eukaryotic Cell

• Double membrane 

• Contain inner folds (cristae) and fluid (matrix) 

• Involved in cellular respiration (ATP production) 

  • 70 S Ribosomes 

  • Circular chromosomes  

  • Replicate on their own 

Chlorplasts

• Locations of photosynthesis 

• Contain flattened membranes (thylakoids) that contain chlorophyll 

  • 70 S Ribosomes 

  • Circular chromosomes 

  • Replicate on their own 

Peroxisomes

• Oxidize fatty acids, destroy H2O2 

Centrosomes 

• Networks of protein fibers and centrioles  

• Form the mitotic spindle; critical role in cell division 

Eukaryotic Ribosomes 

• 80S ribosomes (40S + 60S) 

  • Bigger than prokaryotic ribosome 

  • Sediment differently 

• Consist of proteins and ribosomal RNA 

• Site of protein synthesis 

  • Contain 18S rRNA subunits  

  • Important for identification 

The Evolution of Eukaryotes 

• Life arose as simple organisms 3.5 to 4 billion years ago 

• First eukaryotes evolved 2.5 billion years ago 

• Endosymbiotic theory 

  • Larger bacterial cells engulfed smaller bacterial cells, developing the first eukaryotes 

  • Ingested photosynthetic bacteria became chloroplasts 

  • Ingested aerobic bacteria became mitochondria