Download Chapter 4 Powerpoint (Cellular Structure and

1
4.1 Cellular Level of
Organization
• Detailed study of the cell began in the 1830s
• A unifying concept in biology
• Originated from the work of biologists Schleiden
and Schwann in 1838-39
• Cell Theory:
 All organisms are composed of cells
 All cells come only from preexisting cells
 Cells are the smallest structural and functional unit of
organisms
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Sizes of Living Things
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
0.1 nm
1 nm
10 nm
100 nm
1
m
10
m
100
m 1 mm
1 cm
0.1 m
1m
10 m
100 m 1 km
protein
chloroplast
amino
acid
plant and
animal
cells
rose
mouse
frog egg
virus
most bacteria
human egg
ant
ostrich
egg
atom
blue whale
human
electron microscope
light microscope
human eye
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Cell Size
• Cells range in size from one millimeter down to
one micrometer
• Cells need a large surface area of plasma
membrane to adequately exchange materials.
• The surface-area-to-volume ratio requires that
cells be small
 Large cells - surface area relative to volume
decreases
 Small cells – larger surface area to volume ratio is
advantageous for exchanging molecules
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Microscopy Today: Compound
Light Microscope
• Light passed through specimen
• Focused by glass lenses
• Image formed on human retina
• Max magnification about 1000X
• Resolves objects separated by 0.2 mm, 500X
better than human eye
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Compound Light Microscope
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
85 µm
amoeba, light micrograph
eye
ocular lens
light rays
objective lens
specimen
condenser lens
light source
a. Compound light microscope
© Robert Brons/Biological Photo Service
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Microscopy Today: Transmission
Electron Microscope
• Abbreviated T.E.M.
• Electrons passed through specimen
• Focused by magnetic lenses
• Image formed on fluorescent screen
 Similar to TV screen
 Image is then photographed
• Greater magnification than Compound Light
Microscope
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Transmission Electron
Microscope
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
200 nm
pseudopod segment, transmission electron
micrograph
electron source
electron beam
electromagnetic
condenser lens
specimen
electromagnetic
objective lens
electromagnetic
projector lens
observation screen
or
photographic plate
b. Transmission electron microscope
© M. Schliwa/Visuals Unlimited
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Microscopy Today: Scanning
Electron Microscope
• Abbreviated S.E.M.
• Specimen sprayed with thin coat of metal
 Electron beam scanned across surface of specimen
 Metal emits secondary electrons
• Emitted electrons focused by magnetic lenses
• Image formed on fluorescent screen
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Scanning Electron
Microscope
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
500 µm
amoeba, scanning electron micrograph
electron gun
electron beam
electromagnetic
condenser
lenses
scanning coil
final
condenser
lens
secondary
electrons
specimen
electron
detector
TV
viewing
screen
c. Scanning electron microscope
© Kessel/Shih/Peter Arnold, Inc.
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4.2 Prokaryotic Cells
• Lack a membrane-bound nucleus
• Structurally smaller and simpler than eukaryotic
cells (which have a nucleus).
• Prokaryotic cells are placed in two taxonomic
domains:
 Bacteria
 Archaea
• Live in extreme habitats
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The Structure of Prokaryotes
• Extremely small: 1–1.5 μm wide and 2–6 μm long
• Occur in three basic shapes:
 Spherical coccus,
 Rod-shaped bacillus,
 Spiral spirillum (if rigid) or spirochete (if flexible).
• Cell Envelope includes:
 Plasma membrane - lipid bilayer with imbedded and peripheral
protein
 Cell wall - maintains the shape of the cell and is strengthened by
peptidoglycan
 Glycocalyx - layer of polysaccharides on the outside of the cell
wall
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The Structure of
Prokaryotes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
spirillum
spirochete
bacillus
coccus
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Prokaryotic Cytoplasm and
Appendages
• Cytoplasm
 Semifluid solution
• Bounded by plasma membrane
• Contains water, inorganic and organic molecules, and enzymes
 Nucleoid is a region that contains the single, circular DNA
molecule
 Plasmids are small accessory (extrachromosomal) rings of DNA
• Appendages
 Flagella – provide motility
 Fimbriae – small, bristle-like fibers that sprout from the cell
surface
 Conjugation pili – rigid tubular structures used to pass DNA
from cell to cell
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The Structure of Prokaryotes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Ribosome:
site of protein synthesis
Inclusion body:
stored nutrients for
later use
Mesosome:
plasma membrane
that folds into the
cytoplasm and
increases surface area
Fimbriae:
hairlike bristles that
allow adhesion to
the surfaces
Conjugation pilus:
elongated, hollow
appendage used for
DNA transfer to other
bacterial cells
Nucleoid:
location of the bacterial
chromosome
Plasma membrane:
sheath around cytoplasm
that regulates entrance
and exit of molecules
Cell wall:
covering that supports,
shapes, and protects cell
Glycocalyx:
gel-like coating outside
cell wall; if compact, called
a capsule; if diffuse, called
a slime layer
Flagellum:
rotating filament present
in some bacteria that
pushes the cell forward
Escherichia coli
© Howard Sochurek/The Medical File/Peter Arnold, Inc.
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4.3 Introducing Eukaryotic
Cells
• Cells contain:
 Membrane-bound nucleus that houses DNA
 Specialized organelles
 Plasma membrane
• Much larger than prokaryotic cells
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Origin of Organelles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Original
prokaryotic cell
DNA
1. Cell gains a nucleus by the
plasma membrane invaginating
and surrounding the DNA
with a double membrane.
Nucleus allows specific functions
to be assigned, freeing up cellular
resources for other work.
2. Cell gains an endomembrane
system by proliferation
of membrane.
Increased surface area allows
higher rate of transport of
materials within a cell.
3. Cell gains mitochondria.
aerobic
bacterium
Ability to metabolize sugars in
the presence of oxygen enables
greater function and success.
mitochondrion
4. Cell gains chloroplasts.
Ability to produce
sugars from sunlight
enables greater
function and success.
chloroplast
Animal cell
has mitochondria,
but not chloroplasts.
photosynthetic
bacterium
Plant cell
has both mitochondria
and chloroplasts.
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Eukaryotic Cells: Organelles
• Eukaryotic cells are compartmentalized
 They contain small structures called organelles
• Perform specific functions
• Isolates reactions from others
• Two classes of organelles:
 Endomembrane system
• Organelles that communicate with one another
– Via membrane channels
– Via small vesicles
 Energy related organelles
• Mitochondria and chloroplasts
• Independent and self-sufficient
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Animal Cell Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
mitochondrion
chromatin
nucleolus
nuclear
envelope
Plasma membrane:
outer surface that
regulates entrance and
exit of molecules
endoplasmic
reticulum
protein
2.5 µm
phospholipid
Nucleus: command center of cell
• Nuclear envelope: double
membrane with nuclear pores
that encloses nucleus
Cytoskeleton: maintains
cell shape and assists movement
of cell parts:
• Chromatin: diffuse threads
containing DNA and protein
• Nucleolus: region that produces
subunits of ribosomes
Endoplasmic reticulum:
protein and lipid metabolism
• Microtubules: protein
cylinders that move
organelles
• Intermediate filaments:
protein fibers that provide
stability of shape
• Rough ER: studded with
ribosomes that synthesize
proteins
• Actin filaments: protein
fibers that play a role in
cell division and shape
• Smooth ER: lacks
ribosomes, synthesizes
lipid molecules
Centrioles*: short
cylinders of microtubules
Peroxisome: vesicle
that is involved in
fattyacid metabolism
Centrosome: microtubule
organizing center that
contains a pair of centrioles
Ribosomes:
particles that carry
out protein synthesis
Lysosome*: vesicle that
digests macromolecules
and even cell parts
Vesicle: small membranebounded sac that stores
and transports substances
Polyribosome: string of
ribosomes simultaneously
synthesizing same protein
Mitochondrion: organelle
that carries out cellular respiration,
producing ATP molecules
Cytoplasm: semifluid
matrix outside nucleus
that contains organelles
Golgi apparatus: processes, packages,
and secretes modified proteins
*not in plant cells
© Dr. Dennis Kunkel/Visuals Unlimited
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Plant Cell Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
peroxisome
mitochondrion
nucleus
ribosomes
central vacuole
plasma membrane
cell wall
chloroplast
1 µm
Nucleus: command center of cell
Central vacuole*: large, fluid-filled
sac that stores metabolites and
helps maintain turgor pressure
• Nuclear envelope: double membrane with
nuclear pores that encloses nucleus
• Nucleolus: produces subunits of ribosomes
Cell wall of adjacent cell
• Chromatin: diffuse threads containing
DNA and protein
• Nuclear pore: permits passage of
proteins into nucleus and ribosomal
subunits out of nucleus
Middle lamella:
cements together the
primary cell walls of
adjacent plant cells
Ribosomes: carry
out protein synthesis
Chloroplast*: carries
out photosynthesis,
producing sugars
Centrosome:
microtubule organizing
center (lacks centrioles)
Granum*: a stack
of chlorophyllcontaining thylakoids
in a chloroplast
Endoplasmic
reticulum : protein
and lipid metabolism
• Rough ER: studded
with ribosomes that
synthesize proteins
Mitochondrion: organelle
that carries out cellular
respiration, producing
ATP molecules
• Smooth ER: lacks
ribosomes, synthesizes
lipid molecules
Microtubules: protein cylinders
that aid movement of organelles
Peroxisome: vesicle that
is involved in fatty acid
metabolism
Actin filaments: proteinfibers
that play a role in cell division
and shape
Golgi apparatus: processes,
packages, and secretes
modified proteins
Cytoplasm: semifluid matrix outside
nucleus that contains organelles
Plasma membrane: surrounds
cytoplasm, and regulates entrance
and exit of molecules
Cell wall*: outer surface that shapes,
supports, and protects cell
*not in animal cells
© Newcomb/Wergin/Biological Photo Service (FIRST USE)
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4.4 The Nucleus and
Ribosomes
• The Nucleus
 Command center of cell, usually near center
 Separated from cytoplasm by nuclear envelope
• Consists of double layer of membrane
• Nuclear pores permit exchange between nucleoplasm &
cytoplasm
 Contains chromatin in semifluid nucleoplasm
• Chromatin contains DNA of genes, and proteins
• Condenses to form chromosomes
– Chromosomes are formed during cell division
 Dark nucleolus composed of rRNA
• Produces subunits of ribosomes
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Anatomy of the Nucleus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
nuclear
envelope
nucleolus
Nuclear envelope:
inner membrane
outer membrane
nuclear pore
nuclear
pore
chromatin
nucleoplasm
phospholipid
(Bottom): Courtesy Ron Milligan/Scripps Research Institute; (Top right): Courtesy E.G. Pollock
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Ribosomes
• Are the site of protein synthesis in the cell
• Composed of rRNA
 Consists of a large subunit and a small subunit
 Subunits made in nucleolus
• May be located:
 On the endoplasmic reticulum (thereby making it
“rough”), or
 Free in the cytoplasm, either singly or in groups,
called polyribosomes
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Function of Ribosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nucleus
1. mRNA is first copied from a gene,
and then it exits the nucleus through
a pore complex. A ribosome attaches
and begins protein synthesis,
producing a signal peptide.
mRNA
DNA
ribosome
mRNA
signal peptide
nuclear
pore
ribosomal
subunits
2. Signal recognition particle
(SRP) binds to signal peptide
and temporarily halts protein
synthesis.
signal recognition
particle (SRP)
receptor
Cytoplasm
3. SRP binds to
receptor (purple);
a channel opens;
SRP leaves and
allows protein
synthesis to
resume; as
polypeptide is
synthesized it is
simultaneously
fed into ER.
Lumen of ER
Endoplasmic
reticulum (ER)
ER membrane
mRNA
SRP
enzyme
4. An enzyme removes
the signal peptide from
the growing polypeptide.
5. Ribosomal subunits
and mRNA break away.
The polypeptide remains
in the ER an`d folds into
a functional protein.
protein
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4.5 The Endomembrane
System
• Series of intracellular membranes that
compartmentalize the cell
• Restrict enzymatic reactions to specific
compartments within cell
• Consists of:
 Nuclear envelope
 Membranes of endoplasmic reticulum
 Golgi apparatus
 Vesicles
• Several types
• Transport materials between organelles of system
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Endoplasmic Reticulum
• A system of membrane channels and saccules (flattened vesicles)
continuous with the outer membrane of the nuclear envelope
• Rough ER
 Studded with ribosomes on cytoplasmic side
 Protein anabolism
• Synthesizes proteins
• Modifies and processes proteins
• Smooth ER




No ribosomes
Synthesis of lipids
Site of various synthetic processes, detoxification, and storage
Forms transport vesicles
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Endoplasmic Reticulum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ribosomes
Nuclear envelope
rough
endoplasmic
reticulum
smooth
endoplasmic
reticulum
0.08 µm
© R. Bolender & D.Fawcett/Visuals Unlimited
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The Golgi Apparatus
• Golgi Apparatus
 Consists of flattened, curved saccules
 Resembles stack of hollow pancakes
 Modifies proteins and lipids
• Receives vesicles from ER on cis (or inner face)
• Packages them in vesicles
• Prepares for “shipment” and packages them in
vesicles from trans (or outer face)
• Vesicular Transport
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Golgi Apparatus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
secretion
transport saccules
vesicle
transport
vesicles
trans face
cis face
Golgi apparatus
Nucleus
0.1µm
Courtesy Charles Flickinger, from Journal of Cell Biology 49:221-226, 1971, Fig. 1 page 224
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Lysosomes
• Membrane-bound vesicles (not in plants)
 Produced by the Golgi apparatus
 Contain powerful digestive enzymes and are highly
acidic
• Digestion of large molecules
• Recycling of cellular resources
• Some genetic diseases
 Caused by defect in lysosomal enzyme
 Lysosomal storage diseases (Tay-Sachs)
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Endomembrane System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Consumption
Secretion
5. Secretion
plasma
membrane
4. Secretory vesicle
fuses with the plasma
membrane as secretion
occurs.
Incoming vesicle
brings substances
into the cell that are
digested when the
vesicle fuses with a
lysosome.
enzyme
3. Golgiapparatus
modifies lipids and proteins
from the ER; sorts them
and packages them in
vesicles.
Lysosome
Contains digestive enzymes
that breakdown worn-out
cell parts or substances
entering the cell at the
plasma membrane.
protein
2. Transport vesicle
shuttles proteins to
various locations such as
the Golgi apparatus.
Transport vesicle
shuttles lipids to various
locations such as the
Golgi apparatus.
lipid
1. Rough endoplasmic
reticulum
synthesizes proteins and
packages them in vesicles;
vesicles commonly go to
the Golgi apparatus
Smooth endoplasmic
reticulum
synthesizes lipids and
also performs various
other functions.
ribosome
Nucleus
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4.6 Other Vesicles and
Vacuoles
• Peroxisomes
 Similar to lysosomes
• Membrane-bounded vesicles
• Enclose enzymes
 However
• Enzymes synthesized by free ribosomes in cytoplasm
(instead of ER)
• Active in lipid metabolism
• Catalyze reactions that produce hydrogen peroxide H2O2
– Toxic
– Broken down to water & O2 by catalase
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Vacuoles
• Membranous sacs that are larger than vesicles
 Store materials that occur in excess
 Others very specialized (contractile vacuole)
• Plants cells typically have a central vacuole
 Up to 90% volume of some cells
 Functions in:
• Storage of water, nutrients, pigments, and waste products
• Development of turgor pressure
• Some functions performed by lysosomes in other eukaryotes
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Plant Cell Central Vacuole
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
100 nm
© Newcomb/Wergin/Biological Photo Service
34
4.7 Energy-Related Organelles
• Chloroplasts
 Bounded by double membrane
 Inner membrane infolded
• Forms disc-like thylakoids, which are stacked to form grana
• Suspended in semi-fluid stroma
 Green due to chlorophyll
• Green photosynthetic pigment
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Chloroplasts
• Membranous organelles (a type of plastid) that serve as the site of
photosynthesis
• Captures light energy to drive cellular machinery
• Photosynthesis
 Synthesizes carbohydrates from CO2 & H2O
 Makes own food using CO2 as only carbon source
 Only plants, algae, and certain bacteria are capable of conducting
photosynthesis
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Chloroplast Structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
500 nm
outer
membrane
double
membrane
inner
membrane
grana
thylakoid
stroma space thylakoid membrane
b.
Courtesy Herbert W. Israel, Cornell University
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Mitochondria
•
Smaller than chloroplast
•
Contain ribosomes and their own DNA
•
Surrounded by a double membrane

Inner membrane surrounds the matrix and is convoluted (folds) to
form cristae.

Matrix – Inner semifluid containing respiratory enzymes
•
Break down carbohydrates
•
Involved in cellular respiration
•
Produce most of ATP utilized by the cell
38
Mitochondrion Structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
double
membrane
200 nm
outer
membrane
inner
membrane
cristae
matrix
b.
Courtesy Dr. Keith Porter
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4.8 The Cytoskeleton
• Maintains cell shape
• Assists in movement of cell and organelles
• Three types of macromolecular fibers
 Actin filaments
 Intermediate filaments
 Microtubules
• Assemble and disassemble as needed
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Actin Filaments
• Extremely thin filaments like twisted pearl
necklace
• Dense web just under plasma membrane
maintains cell shape
• Support for microvilli in intestinal cells
• Intracellular traffic control
 For moving stuff around within cell
 Cytoplasmic streaming
• Function in pseudopods of amoeboid cells
• Important component in muscle contraction
(other is myosin)
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Intermediate Filaments
• Intermediate in size between actin filaments and
microtubules
• Rope-like assembly of fibrous polypeptides
• Vary in nature
• Function:
 Support nuclear envelope
 Cell-cell junctions, like those holding skin cells tightly
together
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Microtubules
• Hollow cylinders made of two globular proteins
called a and b tubulin
• Spontaneous pairing of a and b tubulin
molecules form structures called dimers
• Dimers then arrange themselves into tubular
spirals of 13 dimers around
• Assembly:
 Under control of Microtubule Organizing Center
(MTOC)
 Most important MTOC is centrosome
• Interacts with proteins kinesin and dynein to
cause movement of organelles
43
The Cytoskeleton
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
actin
subunit
Chara
a. Actin filaments
fibrous
subunits
peacock
b. Intermediate filaments
tubulin
dimer
chameleon
c. Microtubules
a(Actin): © M. Schliwa/Visuals Unlimited; b, c(Intermediate, Microtubules): © K.G. Murti/Visuals Unlimited; a(Chara): The McGraw-Hill Companies, Inc./photo by
Dennis Strete and Darrell Vodopich; b(Peacock): © Vol. 86/Corbis; c(Chameleon): © Photodisc/Vol. 6/Getty Images
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Centrioles
• Short, hollow cylinders
 Composed of 27 microtubules
 Microtubules arranged into 9 overlapping triplets
• One pair per animal cell
 Located in centrosome of animal cells (not in plants)
 Separate during mitosis to determine plane of division
• May give rise to basal bodies of cilia and
flagella
45
Centrioles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
empty center
of centriole
one microtubule
triplet
one centrosome: one pair of centrioles
two centrosomes: two pairs of centrioles
200 nm
(Middle): Courtesy Kent McDonald, University of Colorado Boulder; (Bottom): Journal of Structural Biology, Online by Manley McGill et al. Copyright 1976 by Elsevier
Science & Technology Journals. Reproduced with permission of Elsevier Science & Technology Journals in the format Textbook via Copyright Clearance Center
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Inner Life of a Cell
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