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Functional Anatomy of Prokaryotic and Eukaryotic Cells

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Title: Functional Anatomy of Prokaryotic and Eukaryotic Cells


1
  • Chapter 4
  • Functional Anatomy of Prokaryotic and Eukaryotic
    Cells

2
Prokaryote Eukaryote
True nucleus
Pre-nucleus
  • Paired chromosomes, in nuclear membrane
  • Histones bound to DNA
  • Membrane-bound organelles
  • Simpler cell walls (polysaccharide)
  • Mitosis
  • One circular chromosome, not in a membrane
  • No histones
  • No membrane-bound organelles
  • Complex cell walls (peptidoglycan in bacteria)
  • Binary fission

3
Prokaryotic Cells Morphology
  • Average size 0.2 -2.0 µm in diameter
  • 2.0-8.0 µm in length
  • Basic shapes/morphologies

Coccus (spherical)
Bacillus (rod-shaped)
Spiral
Coccobacillus
4
Prokaryotic cells Arrangements
  • Pairs diplo- diplococci
    diplobacilli
  • Chains strepto- streptococci streptobacilli
  • Clusters staphylo-staphylococci

5
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
http//lecturer.ukdw.ac.id/dhira/BacterialStructur
e/SurfaceStructs.html
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

Figure 4.8
8
Prokaryotic cell structures Flagella
Flagella Arrangement
( flagella at both poles)
(flagella distributed over the entire cell)
(tuft from one pole)
Figure 4.7
9
Prokaryotic cell structures FlagellaMotility
Taxis movement toward or away from a
stimulus -chemotaxis -phototaxis
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

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

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)

15
Prokaryotic cell structures Cell
WallPeptidoglycan (or murein)
  • Macromolecular network
  • Polymer of a repeating disaccharide unit
    (backbone)
  • Backbones linked by polypeptides

Figure 4.13a
16
Prokaryotic cell structures Gram-positive Cell
Walls
Gram-positive cell wall
  • 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

17
Prokaryotic cell structures Gram-negative Cell
Walls
Gram-negative cell wall
  • 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
Prokaryotic cell structures Cell Walls
Gram-positive cell walls
Gram-negative cell walls
  • Thin peptidoglycan
  • No teichoic acids
  • Outer membrane
  • Lipopolysaccharide
  • Porins
  • Thick peptidoglycan
  • Teichoic acids

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 WallAtypical
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)

21
Prokaryotic cell structures Cell WallDamage 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

22
Prokaryotic cells Structures internal to the
cell wall
23
Prokaryotic cell structuresPlasma Membrane
  • Phospholipid bilayer
  • Proteins
  • Fluid Mosaic Model
  • Membrane is as viscous as olive oil
  • Proteins move to function
  • Phospholipids rotate and move laterally

Figure 4.14b
24
Prokaryotic cell structuresPlasma 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 structuresPlasma 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)

26
Prokaryotic cell structuresPlasma 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 structuresPlasma Membrane
Three types of osmotic solutions
Hypotonic solution
Isotonic solution
Hypertonic solution
solsolution solcell
solsolution lt solcell
solsolution gt solcell
Osmotic lysis
Plasmolysis
solcell concentration of solute inside the
cell
Figure 4.18c-e
28
Prokaryotic cell structuresPlasma Membrane
Movement across membranes Active Transport
Processes
  • Active transport of substances requires a
    transporter protein and ATP
  • Solute movement
    up/against its

    concentrationgradient
  • Important when
    nutrients are scarce

29
Prokaryotic cell structuresOther 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 structuresOther Internal
Structures
  • Ribosomes machinery for protein synthesis
    (translation)
  • Tens of thousands of ribosomes per cell

Complete 70S ribosome
31
Prokaryotic cell structuresOther 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
  • Energy reserves
  • Energy reserves
  • Ribulose 1,5-diphosphate carboxylase for CO2
    fixation
  • Protein covered cylinders
  • Iron oxide (destroys H2O2)

32
Prokaryotic cell structuresOther 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 endospores coat

33
Stained pus from a mixed anaerobic infection
http//qlab.com.au
www.textbookofbacteriology.net
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
  • Cell walls
  • 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 cells 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 3.5-4 byo
  • Eukaryotes 2.5 byo
  • Mitochondria and chloroplasts share properties
    with prokaryotes
  • Reproduce independently of cell
  • Size/shape
  • Circular DNA
  • Their ribosomes are 70S

44
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