Chapter 4
Comparing Prokaryotic and
Eukaryotic Cells
Prokaryotic vs. Eukaryotic Cells
•
Prokaryotic cells
ü No nucleus
ü No organelles
ü Cell walls composed
of peptidoglycan
ü Reproduce asexually via
binary fission
ü One circular chromosome
ü DNA not associated with
histones
Eukaryotic cells
Nucleus
Membrane--bound
Membrane
organelles
Simple cell walls
composed of cellulose
or chitin
Cell division via mitosis
Linear chromosomes
DNA associated with
histone proteins at
times
Prokaryotic Cells
ØSize:
ØLength= 2 to 8 um
ØDiameter= .2 to 2 um
ØMorphology:
ØCocci
ØBacilli
ØSpiral
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Arrangements
Ø Common bacterial arrangements
Ø Diplo
Ø Strepto
Ø Staphylo
Ø Tetrads
Ø Sarcinae
Note: some bacteria are pleomorphic
( have many different shapes)
Bacterial Arrangements
Structures External to
the Prokaryotic Cell Wall
1) GlycocalyxGlycocalyx-sticky, gelatinous substance
that surrounds bacterial cells
Ø
Ø
Ø
Made of polysaccharide or polypeptide or both
Mainly produced inside cell and excreted to
cell surface
Three forms:
a) Capsule
b) Slime layer
c) EPS (extracellular
(extracellular polysaccharide)
* ExampleExample- Streptococcus mutans (teeth)
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More structures outside bacterial cell wall
2) Flagella-long, filamentous appendage
used for locomotion
Four flagella arrangements:
a) Monotrichous-1 flagella
b) Amphitrichous-1 flagella at each
end of the cell
c) Lophotrichous-2 or more flagella at one
end of the cell
d) Peritrichous-many flagella surround
entire cell
Motility
•
•
•
Most spiral bacteria are motile
About ½ of bacilli are motile
Most cocci are nonnon-motile
Advantages of motility:
1) TaxisTaxis-movement towards or away
from stimulus
a) chemotaxis
b) phototaxis
c) aerotaxis
More structures outside
bacterial cell wall
3) Axial filaments: provide means
of motility in spirochetes
a) movement resembles
corkscrew
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More structures outside
bacterial cell wall
4) Fimbriae and Pili
a) FimbriaeFimbriae-short, numerous
hairlike appendages used for
attachment, not motility
*found mainly in Gram (–
(–) microbes
b) PiliPili-long, thin appendage
*usually 1 or 2 per cell
*function*function-join cells to allow transfer
of DNA from cell to cell
Cell Wall
Ø Complex, semisemi-rigid structure
composed primarily of peptidoglycan
Ø Functions:
Ø cell shape
Ø attachment point for flagella
Ø prevent cell lysis due to greater water
pressure inside cell vs outside cell
Ø used to differentiate bacterial cell types
Ø site of action for some antibiotics
Cell Wall Structure
•
PeptidoglycanPeptidoglycan-backbone made of
repeating dissacharide units linked
with polypeptide crossbridges
a) Disaccharide portion made of NAG and
NAM (both monosaccharides)
monosaccharides)
ü
ü
NAG=NNAG=N- acetylglucosamine
NAM=NNAM=N-acetylmuramic acid
b) CrossbridgeCrossbridge-made of numerous amino
acid molecules(peptides)
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Bacterial Cell Wall Structure
Gram (+) Cell Walls
• Contain thick layer of peptidoglycan
• Techoic acidsacids-ROH & P
a) cell growth, prevent cell lysis,
lysis, antigenic
specificity
b) Two types:
*lipoteichoiclipoteichoic-links peptidoglycan layer to
cell membrane
*wall*wall-links peptidoglycan layer only
• NAG & NAM
• Tetrapeptide side chains
• Amino acid crossbridges
Gram + Cell Wall
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Gram ((-) Cell Walls
• Thin peptidoglycan layerlayer-more
susceptible to damage
• NAG & NAM
• Tetrapeptide side chains
• Amino acid crossbridges
• NO TECHOIC ACIDS
• 2nd Outermembrane
Gram – Cell Walls
Outermembrane of Gram
(-) Cell Wall
• Made of lipopolysaccharides (LPS),
lipoproteins, and phospholipids
• Contains porins
• 2nd outermembraneoutermembrane-Characteristics:
– Lipid AA-endotoxin (causes fever/shock)
– O polysaccharidepolysaccharide-Antigen
• Function:
– Evade phagocytosis
– Barrier to antibiotics, dyes, digestive
enzymes
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Bacterial Cell Wall
Damage
• Chemically unique from any
other animal cell structure
• Target for drugs that attack and
kill bacteria with harming host
cell
– Selective Toxicity= kills microbe
but doesn’t harm host
– Many antibiotics directed at cell
wall synthesis
Damage to Cell Wall
Continued…
• Lysozyme
– Digestive enzyme that damages
bacterial cell walls
– Found in tears and saliva
– Attacks bond between NAM & NAG
– Works best on Gram (+) cells
– If cell wall not complete, water
rushes in and LYSIS occurs
Structures Internal to
Cell Wall
1) Plasma (Cell) Membrane
a) thin membrane enclosing
cytoplasm
b) Composed of double layer of
phospholipid and proteins
c) Fluid Mosaic Model
* substances move freely
within membrane
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Cell Membrane
Components
1) Phospholipid bilayer
– Polar heads (made of phosphate
and glycerol)
*hydrophilic (loves water)
– Nonpolar tails (made of fatty acids)
*hydrophobic (water hating)
Cell Membrane Components Continued
2) Proteins: Two types:
a) PeripheralPeripheral-located only on the edge of
inner or outer surface of membrane
*Easily removed
*Function*Function-support, act as enzymes
b) IntegralIntegral-extends all the way through
bilayer
*Difficult to remove
*Function*Function- act as channels that allow
substances to move in/out of cell
Cell membrane structure
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Functions of Cell
Membrane
1) BarrierBarrier-selectively permeability
determines what molecules
pass through membrane
a) large(protein, starch, etc.)
don’t pass through easily
b) small (H2O, O2, CO2) pass
through easily
Movement of Materials
Across Cell Membranes
• Two types of processes:
1) PassivePassive-high to low
concentration (no energy used)
a) ExamplesExamples-osmosis, simple
diffusion, facilitated diffusion
2) ActiveActive-low to high
concentration (uses energy)
a) ExamplesExamples-active transport
Passive Processes
1) Simple diffusiondiffusion-molecules/ions move from area
of high to low concentration until they are evenly
distributed (equilibrium)
– ExamplesExamples-O2 and CO2
2) OsmosisOsmosis-water molecules move from high to low
concentration
3) Facilitated diffusiondiffusion-substance being
transported needs assistance from a plasma
membrane protein (transporter protein)
- ExampleExample-glucose
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Principles of Osmosis
Active Processes
1) Active TransportTransport-transporter
proteins move substances
across cell membrane while
using energy (ATP)
Cell Membrane
Functions Continued
2) Secrete exoenzymes that
breakdown nutrients to provide
energy
a) ExamplesExamples-amylase & lipase
3) ETS found here
4) Cell wall synthesis enzymes
located here
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Antimicrobial Agents
• Antiseptics and Disinfectants
– Often disrupt cell membrane and
cause cell death (membrane lysis)
lysis)
Cytoplasm
• Substance located within cell
membrane
– 80% water (other(other-protein, carbs,
carbs,
lipids, inorganic ions)
– Thick, elastic, semitransparent
– Contains DNA and ribosomes
Nuclear Area (nucleoid
(nucleoid))
• Contains 1 single, long, circular
ds DNA (called ccDNA)
ccDNA)
*Function*Function-carries all info
required for cell structure &
function
*plasmids also in nucleoid
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Prokaryote structure
Plasmids
• Small, circular, extraextra-chromosomal
DNA
• 5-100 genes
• Carry genes for antibiotic resistance,
synthesis of enzymes, and
production of toxins
• Transferred from 1 bacteria to
another
• Replicate independently from ccDNA
Ribosomes
• Site of protein synthesis
• Two subunitssubunits-each made of
protein and ribosomal RNA
– Prokaryotic: 70 S (50 S & 30 S)
– Eukaryotic:
Eukaryotic: 80 S (60 S & 40 S)
*S (Svedberg
(Svedberg unit)unit)-function of size,
weight, and shape
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Prokaryotic ribosome
Selective Toxicity
• Some antibiotics aimed at 70S
ribosome of bacterial cells
*Streptomycin*Streptomycin-attach to 30S
subunit and disrupt protein
synthesis
*Erythromycin*Erythromycin-attach of 50 S
subunit and interferes with
protein synthesis
Inclusions
• Reserve deposits found in
prokaryotic cytoplasm
Examples:
a) lipidlipid-fat
b) gas vacuolesvacuoles-buoyancy
c) polysaccharidepolysaccharide-starch
d) metachromaticmetachromatic-inorganic
phosphate (create ATP)
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Endospores
• Formed by some bacteria to survive
harsh environmental conditions (dry,
extreme temp, pH, salinity,
chemicals)chemicals)-viable for up to 7500 yrs!
• CryptobioticCryptobiotic-no metabolic activity
• Survive boiling up to 20 hours
– Vegetative cellscells-killed above 70C
• Found in Gram + only
-Bacillus and Clostridium genera
Eukaryotic Cell
Organelles
• NucleusNucleus-contains genetic
material (DNA)
• NucleolusNucleolus-inside nucleusnucleusproduces ribosomal RNA
(ribosome component)
• Golgi bodybody-modify, sort,
package, and transport proteins
(shipping/receiving area of cell)
Eukaryotic cell
organelles (continued)
• Endoplasmic reticulum (E.R.)
– Membraneous network connecting cell
and nuclear membrane
– Function= surface for chemical
reactions, transportation network, stores
chemical molecules
– Two types:
• sERsER-smoothsmooth-no ribosomes (lipid synthesis)
• rERrER-roughrough-ribosomes (protein synthesis)
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Eukaryotic cell
organelles (continued)
• RibosomesRibosomes-protein synthesis
– 80 S
• LysosomesLysosomes-store degradative
enzymes
• MitochondriaMitochondria-site of ATP production
– Contain 70 S ribosomes
– Circular chromosome
– Replicate on its own (binary fission)
Eukaryotic cell
organelles (continued)
• ChloroplastsChloroplasts-house chlorophyll
and enzymes needed for
photosynthesis
– 70 S ribosome
– Circular chromosome
– Replicate on its own (binary
fission)
Evolution of Eukaryotes
• Endosymbiotic Theory
ü States that mitochondria and
chloroplasts were once freefree-living
prokaryotes that were engulfed by
amoebaamoeba-like eukaryotic cells
ü Evidence
*same size/shape as bacteria
*70 S ribosome
*circular chromosome
*reproduce independently (binary fission)
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