functional anatomy of prokaryotic and eukaryotic cells lecture 2
TRANSCRIPT
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Functional Anatomy of Prokaryotic and Eukaryotic Cells
Lecture 2
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Sca
le o
f Mic
robe
s
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Comparing Prokaryotic and Eukaryotic Cells
Common features:DNA and chromosomesCell membraneCytosol and Ribosomes
Distinctive features: ?
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Eukaryotic CellEukaryotic Cell(protist, animal)(protist, animal)
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EukaryoEukaryo
Eukaryotic CellEukaryotic Cell(plant)(plant)
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Differences Between Cell Types
Prokaryotic Cell Eukaryotic Cell
Single circular chromosome
Multiple linear chromosomes
Chromosome found in a cytoplasmic region called the nucleoid.
Chromosomes found in a membrane-bound nucleus.
No internal membranes
Some infolded plasma membrane
Extensive network of internal membranes Specialized areas called organelles
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Prokaryotes
One circular chromosome, not membrane bound
No histones No organelles Peptidoglycan cell walls Binary fission
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Size and Shape of Prokaryotic Cells
Average size: 0.2 -1.0 µm 2 - 8 µm
Three basic shapes
1. Bacillus, 2. Coccus, 3. Spirals (Vibrio,
Spirillum, Spirochete)
Most monomorphic, some pleomorphic
Variations in cell arrangements (esp. for cocci)
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Rod-Shaped Bacteria
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Spherical Bacteria
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Spiral-Shaped Bacteria
Spi
roch
ete:
Bor
reli
a bu
rgdo
rfer
i
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Cell Arrangement Pairs: Diplococci,
diplobacilli
Clusters: Staphylococci
Chains: Streptococci, streptobacilli
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Cytoplasm and Internal Structures
Location of most biochemical activities Nucleoid: nuclear region containing DNA
(up to 3500 genes). Most bacterial chromosomes are circular
Plasmids: small, nonessential, circular DNA (5-100 genes); replicate independently
Ribosomes (70S vs. 80S)
Inclusion bodies: granules containing nutrients, monomers, Fe compounds (magnetosomes)
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Prokaryotic CellProkaryotic Cell
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Closed Circular Chromosome
Also Plasmids, which are smaller, circular
pieces of DNA.
Plasmids usually encode
expendable functions, e.g.,
antibiotic resistance.
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Ribosomes: Sites of Translation
On order of 10,000 per cell!
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Internal Structures: Cell MembraneAnalogous to eukaryotic cell membrane: Phospholipid bilayer with proteins (Fluid mosaic
model) Permeability barrier (selectively permeable) Diffusion, osmosis and transport systems
Different from eukaryotic cell membrane: Role in Energy transformation (electron transport
chain for ATP production)
Damage to the membrane by alcohols, quaternary ammonium (detergents), and polymyxin antibiotics causes leakage of cell contents.
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Sim
ple
Diff
usio
n --
Osm
osis
solute molecules/ions
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Cyt
opla
smic
Mem
bran
e
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Pro
tein
-Med
iate
d T
rans
port
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Act
ive
Tra
nspo
rt
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Cell Wall
Rigid for shape & protection prevents osmotic lysis
Consists of Peptidoglycan (murein) polymer of two disaccharide subunits N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
Linked by polypeptides with tetrapeptide side chain attached to NAM
Fully permeable to ions, aa, and sugars (Gram positive cell wall may regulate movement of cations)
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Gram + Cell Wall
Thick layer of peptidoglycan
Negatively charged teichoic acid on surface
Thin peptidoglycan No teichoic acids Outer membrane
Gram – Cell Wall
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Gram-positive Cell Wall
Fig 4.13
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Gram-negative Cell WallLipid A of LPS acts as endotoxin; O antigens for typing, e.g., E. coli O157:H7
Gram neg. bacteria are less sensitive to medications because outer membrane acts as additional barrier.
LPS layer = outer layer of outer membrane
(protein rich gel-like fluid)
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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
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Atypical Bacteria: Mycoplasmas
Lack cell walls
Instead, have cell membrane which incorporates cholesterol compounds (sterols), similar to eukaryotic cells
Cannot be detected by typical light microscopy
This EM shows some typically pleomorph mycoplasmas, in this case M. hyorhinis
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Acid-fast Cell Walls
Genus Mycobacterium and Nocardia
mycolic acid (waxy lipid) covers thin peptidoglycan layer
Do not stain well with Gram stain use acid-fast stain
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Damage to 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.
L forms are wall-less cells that swell into irregular shapes.
Protoplasts and spheroplasts are susceptible to osmotic lysis.
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External Structures located outside of cell wall
Flagella Axial filaments Fimbriae Pili Glycocalyx
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Glycocalyx Many bacteria secrete external surface layer
composed of sticky polysaccharide (EPS), polypeptide, or both
A capsule is neatly organized A slime layer is unorganized and loose Allows cells to attach key to biofilms
Prevents phagocytosis virulence factor
E.g.: B. anthracis, S. pneumoniae, S. mutans
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Flagellum – Flagella Anchored to wall and membrane Number and placement determines if
atrichous, monotrichous, lophotrichous, amphitrichous, or peritrichous
Allows for move toward or away from stimuli: Chemotaxis (phototaxis and magnetotaxis)
Flagella proteins are H antigens (e.g., E. coli O157:H7)
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Fla
gella
r A
rran
gem
ents
also “atrichous”
e.g., E. coli
Polar Flagellum
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Axial Filaments Endoflagella In spirochetes Anchored at one end
of a cell Rotation causes cell
to move
Fimbriae allow attachment
Pili are used to transfer DNA from one cell to another
Fimbriae and Pili
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Fimbriae
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Endospores
Dormant, tough, non-reproductive structure; germination vegetative cells
Spore forming genera: __________
Resistance to UV and radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants
Relationship to disease
Sporulation: Endospore formation
Germination: Return to vegetative state
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