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Chapter 3Chapter 3

Lecture OutlineLecture Outline

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Cellular Form and FunctionCellular Form and Function

Concepts of cellular structureConcepts of cellular structure Cell surfaceCell surface Membrane transportMembrane transport CytoplasmCytoplasm

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Modern Cell TheoryModern Cell Theory

All organisms composed of cells and cell All organisms composed of cells and cell products.products.

Cell is the simplest structural and functional Cell is the simplest structural and functional unit of life. unit of life.

Cells are specializedCells are specialized Cells come only from preexisting cells.Cells come only from preexisting cells. Cells of all species have many fundamental Cells of all species have many fundamental

similarities.similarities.

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Cell ShapesCell Shapes

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Cell Shapes 2Cell Shapes 2

Squamous = thin and flatSquamous = thin and flat Polygonal = irregularly angular with 4 or more Polygonal = irregularly angular with 4 or more

sidessides Cuboidal = squarishCuboidal = squarish Columnar = taller than wideColumnar = taller than wide Spheroid = roundSpheroid = round Discoid = disc-shapedDiscoid = disc-shaped Stellate = starlikeStellate = starlike Fusiform = thick in middle, tapered at endsFusiform = thick in middle, tapered at ends Fibrous = threadlikeFibrous = threadlike

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Cell SizeCell Size

Human cell sizeHuman cell size most from 10 - 15 µm in diametermost from 10 - 15 µm in diameter

nerve cell (very long) at 1 meter longnerve cell (very long) at 1 meter long

Limitations on cell sizeLimitations on cell size cell growth increases volume faster than cell growth increases volume faster than

surface areasurface area• nutrient absorption and waste removal utilize surfacenutrient absorption and waste removal utilize surface

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Cell Surface Area and VolumeCell Surface Area and Volume

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Major Constituents of CellMajor Constituents of Cell

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Cellular OrganellesCellular Organelles

Know the structure and function of the Know the structure and function of the cellular organelles as they are presented cellular organelles as they are presented at at www.cellsalive.comwww.cellsalive.com

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Pair of dark parallel lines around cell Pair of dark parallel lines around cell Defines cell boundariesDefines cell boundaries Controls interactions with other cellsControls interactions with other cells Controls passage of materials in and out Controls passage of materials in and out

of cellof cell

Plasma MembranePlasma Membrane

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Plasma MembranePlasma Membrane

Oily film of lipids with diverse proteins embedded Oily film of lipids with diverse proteins embedded in itin it

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Membrane LipidsMembrane Lipids Plasma membrane = 98% lipidsPlasma membrane = 98% lipids Phospholipid bilayerPhospholipid bilayer

75% of the lipids75% of the lipids molecular motion creates membrane fluiditymolecular motion creates membrane fluidity

CholesterolCholesterol 20% of the lipids20% of the lipids affects membrane fluidity (low concentration more rigid, affects membrane fluidity (low concentration more rigid,

high concentration more fluid)high concentration more fluid) GlycolipidsGlycolipids

5% of the lipids5% of the lipids contribute to glycocalyx (carbohydrate coating on cell contribute to glycocalyx (carbohydrate coating on cell

surface)surface)

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Membrane ProteinsMembrane Proteins

Membrane proteinsMembrane proteins 2% of the molecules in plasma membrane2% of the molecules in plasma membrane 50% of its weight 50% of its weight

Transmembrane proteinsTransmembrane proteins pass completely through membranepass completely through membrane most are glycoproteinsmost are glycoproteins

Peripheral proteinsPeripheral proteins adhere to membrane surfaceadhere to membrane surface anchored to cytoskeletonanchored to cytoskeleton

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Membrane Protein FunctionsMembrane Protein Functions Receptors, enzymes, channel proteins (gates), cell-Receptors, enzymes, channel proteins (gates), cell-

identity markers, cell-adhesion moleculesidentity markers, cell-adhesion molecules

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Membrane ReceptorsMembrane Receptors

Cell communication via chemical signalsCell communication via chemical signals receptors bind these chemicals (hormones, receptors bind these chemicals (hormones,

neurotransmitters)neurotransmitters) receptor specificityreceptor specificity

Receptor activation produces a second Receptor activation produces a second messenger (chemical) inside of the cellmessenger (chemical) inside of the cell

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Second Messenger SystemSecond Messenger System

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Second Messenger SystemSecond Messenger System

Chemical messenger (epinephrine) binds to Chemical messenger (epinephrine) binds to a surface receptora surface receptor

Receptor activates G proteinReceptor activates G protein G protein binds to adenylate cyclase which G protein binds to adenylate cyclase which

converts ATP to cAMP(2converts ATP to cAMP(2ndnd messenger) messenger) cAMP activates a kinase in the cytosol cAMP activates a kinase in the cytosol Kinases activates or inactivates other Kinases activates or inactivates other

enzymes triggering physiological changes in enzymes triggering physiological changes in cell cell

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Membrane EnzymesMembrane Enzymes

Break down chemical messengers to stop Break down chemical messengers to stop their signaling effectstheir signaling effects

Final stages of starch and protein digestion Final stages of starch and protein digestion in small intestine in small intestine

Produce second messengers (cAMP)Produce second messengers (cAMP)

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Membrane Channel ProteinsMembrane Channel Proteins

Transmembrane proteins with pores Transmembrane proteins with pores some constantly opensome constantly open gated-channels open and close in response to gated-channels open and close in response to

stimulistimuli• ligand (chemically)-regulated gates ligand (chemically)-regulated gates • voltage-regulated gatesvoltage-regulated gates• mechanically regulated gates (stretch and pressure)mechanically regulated gates (stretch and pressure)

Important in nerve signal and muscle Important in nerve signal and muscle contractioncontraction

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Membrane Carriers or PumpsMembrane Carriers or Pumps

Transmembrane proteins bind to Transmembrane proteins bind to solutes and transfer them across solutes and transfer them across membranemembrane

Pumps = carriers that consume ATPPumps = carriers that consume ATP

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Membrane Cell-Adhesion MoleculesMembrane Cell-Adhesion Molecules

Adhere cells to each other and to Adhere cells to each other and to extracellular materialextracellular material

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Membrane Cell-Identity MarkersMembrane Cell-Identity Markers

Glycoproteins form the glycocalyxGlycoproteins form the glycocalyx surface coatingsurface coating acts as a cell’s identity tagacts as a cell’s identity tag

Enables body to identify “self” from Enables body to identify “self” from foreign invadersforeign invaders

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GlycocalyxGlycocalyx

Unique fuzzy cell surface Unique fuzzy cell surface carbohydrate portions of membrane carbohydrate portions of membrane

glycoproteins and glycolipidsglycoproteins and glycolipids unique in everyone but identical twinsunique in everyone but identical twins

Functions (see Table 3.2)Functions (see Table 3.2) cell recognition, adhesion and protectioncell recognition, adhesion and protection

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Extensions of membrane (1-2Extensions of membrane (1-2m)m) Some contain actinSome contain actin FunctionFunction

increase surface area for absorptionincrease surface area for absorption• brush border brush border

milking action of actinmilking action of actin• actin filaments shorten microvilliactin filaments shorten microvilli

pushing absorbed contents down into cellpushing absorbed contents down into cell

MicrovilliMicrovilli

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Cross Section of a MicrovillusCross Section of a Microvillus

Note: actin microfilaments are found in center of each microvilli.

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CiliaCilia Hairlike processes 7-10Hairlike processes 7-10m longm long

single, nonmotile cilium found on nearly every cellsingle, nonmotile cilium found on nearly every cell Sensory in inner ear, retina and nasal cavitySensory in inner ear, retina and nasal cavity

Motile ciliaMotile cilia beat in wavesbeat in waves power strokes followed by recovery strokes power strokes followed by recovery strokes

Chloride pumps produce saline layer at cell surface. Floating mucus pushed along by cilia.

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Cross Section of a CiliumCross Section of a Cilium Axoneme has 9 + 2 Axoneme has 9 + 2

structure of microtubulesstructure of microtubules 9 pairs form basal body 9 pairs form basal body

inside the cell membrane inside the cell membrane dynein arms “crawls” up dynein arms “crawls” up

adjacent microtubule adjacent microtubule bending the ciliabending the cilia

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FlagellaFlagella

Whiplike structure with axoneme identical Whiplike structure with axoneme identical to ciliumto cilium much longer than ciliummuch longer than cilium

Tail of the sperm = only functional Tail of the sperm = only functional flagellumflagellum

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Membrane TransportMembrane Transport

Plasma membrane selectively permeablePlasma membrane selectively permeable controls what enters or leaves cellcontrols what enters or leaves cell

Passive transport requires no ATP Passive transport requires no ATP movement down concentration gradientmovement down concentration gradient filtration and simple diffusion filtration and simple diffusion

Active transport requires ATPActive transport requires ATP movement against concentration gradient movement against concentration gradient carrier mediated (facilitated diffusion and active transport)carrier mediated (facilitated diffusion and active transport) vesicular transport vesicular transport

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FiltrationFiltration

Movement of particles through a Movement of particles through a selectively permeable membrane by selectively permeable membrane by hydrostatic pressurehydrostatic pressure

ExamplesExamples filtration of nutrients from blood capillaries into filtration of nutrients from blood capillaries into

tissue fluidstissue fluids filtration of wastes from the blood in the filtration of wastes from the blood in the

kidneyskidneys

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Simple DiffusionSimple Diffusion

Net movement of particles from area of Net movement of particles from area of high concentration to area of low high concentration to area of low concentrationconcentration due to their constant, random motion due to their constant, random motion

Also known as movement down the Also known as movement down the concentration gradientconcentration gradient

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Diffusion RatesDiffusion Rates Factors affecting diffusion rate through a Factors affecting diffusion rate through a

membrane membrane temperature - temperature - temp., temp., motion of particles motion of particles molecular weight - larger molecules move slowermolecular weight - larger molecules move slower steepness of concentrated gradient - steepness of concentrated gradient - difference, difference, rate rate membrane surface area - membrane surface area - area, area, rate rate membrane permeability - membrane permeability - permeability, permeability, rate rate

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Membrane PermeabilityMembrane Permeability

Diffusion through lipid bilayerDiffusion through lipid bilayer Nonpolar, hydrophobic substances diffuse Nonpolar, hydrophobic substances diffuse

through lipid layerthrough lipid layer Diffusion through channel proteinsDiffusion through channel proteins

water and charged hydrophilic solutes diffuse water and charged hydrophilic solutes diffuse through channel proteinsthrough channel proteins

Cells control permeability by regulating Cells control permeability by regulating number of channel proteinsnumber of channel proteins

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OsmosisOsmosis

Diffusion of water Diffusion of water through a membrane through a membrane from area of more water from area of more water

to area of less waterto area of less water Aquaporins = channel Aquaporins = channel

proteins specialized for proteins specialized for osmosisosmosis

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Osmotic PressureOsmotic Pressure

Amount of hydrostatic Amount of hydrostatic pressure required to pressure required to stop osmosis stop osmosis

Osmosis slows due to Osmosis slows due to filtration of water back filtration of water back across membrane due across membrane due to to hydrostatic hydrostatic pressurepressure

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OsmolarityOsmolarity One osmole = 1 mole of dissolved One osmole = 1 mole of dissolved

particlesparticles 1M NaCl ( 1 mole Na1M NaCl ( 1 mole Na++ ions + 1 mole Cl ions + 1 mole Cl-- ions) ions)

thus 1M NaCl = 2 osm/Lthus 1M NaCl = 2 osm/L Osmolarity = # osmoles/liter of solution Osmolarity = # osmoles/liter of solution Physiological solutions are expressed in Physiological solutions are expressed in

milliosmoles per liter (mOsm/L)milliosmoles per liter (mOsm/L) blood plasma = 300 mOsm/Lblood plasma = 300 mOsm/L osmolality similar to osmolarity at osmolality similar to osmolarity at

concentration of body fluidsconcentration of body fluids

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TonicityTonicity

Tonicity - ability of a solution to affect fluid volume Tonicity - ability of a solution to affect fluid volume and pressure within a celland pressure within a cell depends on concentration and permeability of solutedepends on concentration and permeability of solute

Hypotonic solution Hypotonic solution low concentration of nonpermeating solutes (high water low concentration of nonpermeating solutes (high water

concentration) concentration) cells absorb water, swell and may burst (lyse)cells absorb water, swell and may burst (lyse)

Hypertonic solution Hypertonic solution has high concentration of nonpermeating solutes (low has high concentration of nonpermeating solutes (low

water concentration)water concentration) cells lose water + shrivel (crenate)cells lose water + shrivel (crenate)

Isotonic solution = normal saline Isotonic solution = normal saline

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Effects of Tonicity on RBCsEffects of Tonicity on RBCs

Hypotonic, isotonic and hypertonic solutions affect the fluid volume of a red blood cell. Notice the crenated and swollen cells.

3939

Carrier Mediated Transport Carrier Mediated Transport

Proteins carry solutes across cell Proteins carry solutes across cell membranemembrane

SpecificitySpecificity solute binds to a specific receptor site on solute binds to a specific receptor site on

carrier protein carrier protein differs from membrane enzymes because differs from membrane enzymes because

solutes are unchangedsolutes are unchanged Types of carrier mediated transport Types of carrier mediated transport

facilitated diffusion and active transportfacilitated diffusion and active transport

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Membrane CarriersMembrane Carriers

UniporterUniporter carries only one solute at a timecarries only one solute at a time

SymporterSymporter carries 2 or more solutes simultaneously in same carries 2 or more solutes simultaneously in same

direction (cotransport)direction (cotransport) AntiporterAntiporter

carries 2 or more solutes in opposite directions carries 2 or more solutes in opposite directions (countertransport)(countertransport)

• sodium-potassium pump brings in Ksodium-potassium pump brings in K++ and removes Na and removes Na++ from from cellcell

Any carrier type can use either facilitated Any carrier type can use either facilitated diffusion or active transportdiffusion or active transport

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Facilitated DiffusionFacilitated Diffusion Transport of solute across membrane down its Transport of solute across membrane down its

concentration gradientconcentration gradient No ATP usedNo ATP used Solute binds to carrier, it changes shape then releases Solute binds to carrier, it changes shape then releases

solute on other side of membranesolute on other side of membrane

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Active TransportActive Transport

Transport of solute across membrane up Transport of solute across membrane up (against) its concentration gradient(against) its concentration gradient

ATP energy required to change carrier ATP energy required to change carrier Examples:Examples:

sodium-potassium pumpsodium-potassium pump bring amino acids into cellbring amino acids into cell pump Capump Ca2+2+ out of cell out of cell

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Sodium-Potassium PumpSodium-Potassium Pump

Needed because NaNeeded because Na++ and K and K++ constantly leak through constantly leak through membranemembrane half of daily calories utilized for pumphalf of daily calories utilized for pump

One ATP utilized to exchange three NaOne ATP utilized to exchange three Na++ pushed out pushed out for two Kfor two K++ brought in to cell brought in to cell

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Functions of NaFunctions of Na++ -K -K++ Pump Pump Regulation of cell volumeRegulation of cell volume

““fixed anions” attract cations causing osmosisfixed anions” attract cations causing osmosis cell swelling stimulates the Nacell swelling stimulates the Na++-- KK+ + pump to pump to

ion concentration, ion concentration, osmolarity and cell swelling osmolarity and cell swelling Heat production (thyroid hormone increase # of Heat production (thyroid hormone increase # of

pumps; heat a by-product)pumps; heat a by-product) Maintenance of a membrane potential in all cellsMaintenance of a membrane potential in all cells

pump keeps inside negative, outside positivepump keeps inside negative, outside positive Secondary active transport (No ATP used)Secondary active transport (No ATP used)

steep concentration gradient of Nasteep concentration gradient of Na++ and K and K++ maintained maintained across the cell membraneacross the cell membrane

carriers move Nacarriers move Na++ with 2 with 2ndnd solute easily into cell solute easily into cell• SGLT saves glucose in kidneySGLT saves glucose in kidney

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Vesicular TransportVesicular Transport

Transport large particles or fluid droplets Transport large particles or fluid droplets through membrane in vesiclesthrough membrane in vesicles uses ATPuses ATP

Exocytosis –transport out of cell Exocytosis –transport out of cell Endocytosis –transport into cellEndocytosis –transport into cell

phagocytosis – engulfing large particlesphagocytosis – engulfing large particles pinocytosis – taking in fluid dropletspinocytosis – taking in fluid droplets receptor mediated endocytosis – taking in receptor mediated endocytosis – taking in

specific molecules bound to receptorsspecific molecules bound to receptors

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Phagocytosis or “Cell-Eating”Phagocytosis or “Cell-Eating”

Keeps tissues free of debris and infectious microorganisms.

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Pinocytosis or “Cell-Drinking”Pinocytosis or “Cell-Drinking”

Taking in droplets of ECF Taking in droplets of ECF occurs in all human cellsoccurs in all human cells

Membrane caves in, then pinches off into Membrane caves in, then pinches off into the cytoplasm as pinocytotic vesiclethe cytoplasm as pinocytotic vesicle

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TranscytosisTranscytosis

Transport of a substance across a cellTransport of a substance across a cell Receptor mediated endocytosis moves it into cell Receptor mediated endocytosis moves it into cell

and exocytosis moves it out the other side and exocytosis moves it out the other side insulin insulin

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Receptor Mediated EndocytosisReceptor Mediated Endocytosis

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Receptor Mediated EndocytosisReceptor Mediated Endocytosis

Selective endocytosisSelective endocytosis Receptor specificityReceptor specificity Clathrin-coated vesicle in cytoplasmClathrin-coated vesicle in cytoplasm

uptake of LDL from bloodstreamuptake of LDL from bloodstream

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ExocytosisExocytosis

Secreting material or replacement of plasma Secreting material or replacement of plasma membranemembrane

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The CytoplasmThe Cytoplasm

Organelles = specialized tasksOrganelles = specialized tasks bordered by membranebordered by membrane

• nucleus, mitochondria, lysosome, perioxisome, endoplasmic nucleus, mitochondria, lysosome, perioxisome, endoplasmic reticulum, and Golgi complexreticulum, and Golgi complex

not bordered by membranenot bordered by membrane• ribosome, centrosome, centriole, basal bodiesribosome, centrosome, centriole, basal bodies

Cytoskeleton Cytoskeleton microfilaments and microtubulesmicrofilaments and microtubules

InclusionsInclusions stored productsstored products

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NucleusNucleus

Largest organelle (5 Largest organelle (5 m in diameter)m in diameter) some anuclear or multinucleatesome anuclear or multinucleate

Nuclear envelope Nuclear envelope two unit membranes held together at nuclear two unit membranes held together at nuclear

porespores NucleoplasmNucleoplasm

chromatin (thread-like matter) = DNA and chromatin (thread-like matter) = DNA and proteinprotein

nucleoli = dark masses where ribosomes nucleoli = dark masses where ribosomes producedproduced

5454

Micrograph of The NucleusMicrograph of The Nucleus

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Parallel, flattened membranous sacs Parallel, flattened membranous sacs covered with ribosomescovered with ribosomes

Continuous with nuclear envelope and Continuous with nuclear envelope and smooth ERsmooth ER

Synthesis of packaged proteins (digestive Synthesis of packaged proteins (digestive glands) and phospholipids and proteins of glands) and phospholipids and proteins of plasma membraneplasma membrane

Rough Endoplasmic ReticulumRough Endoplasmic Reticulum

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Smooth Endoplasmic ReticulumSmooth Endoplasmic Reticulum

Lack ribosomesLack ribosomes Cisternae more tubular and branchingCisternae more tubular and branching Synthesis of membranes, steroids (ovary Synthesis of membranes, steroids (ovary

and testes) and lipids, detoxification (liver and testes) and lipids, detoxification (liver and kidney), and calcium storage (skeletal and kidney), and calcium storage (skeletal and cardiac muscle)and cardiac muscle)

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Smooth and Rough ERSmooth and Rough ER

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Endoplasmic ReticulumEndoplasmic Reticulum

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RibosomesRibosomes

Granules of protein and RNA Granules of protein and RNA found in nucleoli, free in cytosol and on rough found in nucleoli, free in cytosol and on rough

ERER Uses directions in messenger RNA to Uses directions in messenger RNA to

assemble amino acids into proteins assemble amino acids into proteins specified by the genetic code (DNA)specified by the genetic code (DNA)

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Golgi ComplexGolgi Complex

System of flattened sacs (cisternae)System of flattened sacs (cisternae) Synthesizes carbohydrates, packages Synthesizes carbohydrates, packages

proteins and glycoproteinsproteins and glycoproteins Forms vesiclesForms vesicles

lysosomeslysosomes secretory vesiclessecretory vesicles new plasma membranenew plasma membrane

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Golgi ComplexGolgi Complex

6262

LysosomesLysosomes

Package of enzymes in a single unit Package of enzymes in a single unit membrane, variable in shapemembrane, variable in shape

FunctionsFunctions intracellular digestion of large moleculesintracellular digestion of large molecules autophagy - digestion of worn out organellesautophagy - digestion of worn out organelles autolysis - programmed cell death autolysis - programmed cell death breakdown stored glycogen in liver to release breakdown stored glycogen in liver to release

glucose glucose

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Lysosomes and PeroxisomesLysosomes and Peroxisomes

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PeroxisomesPeroxisomes

Resemble lysosomes but contain different Resemble lysosomes but contain different enzymesenzymes

In all cells but abundant in liver and kidneyIn all cells but abundant in liver and kidney FunctionsFunctions

neutralize free radicals, detoxify alcohol, other drugs neutralize free radicals, detoxify alcohol, other drugs and toxinsand toxins

uses Ouses O2 2 , H, H22OO22 and catalase enzyme to oxidize organic and catalase enzyme to oxidize organic

moleculesmolecules breakdown fatty acids into acetyl groups for breakdown fatty acids into acetyl groups for

mitochondrial usemitochondrial use

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MitochondrionMitochondrion Double unit membraneDouble unit membrane

inner membrane folds called inner membrane folds called cristaecristae

• ATP synthesized by enzymes on ATP synthesized by enzymes on cristae from energy extracted from cristae from energy extracted from organic compoundsorganic compounds

Space between cristae called Space between cristae called matrixmatrix contains ribosomes and small, contains ribosomes and small,

circular DNA molecule (mtDNA)circular DNA molecule (mtDNA)

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EM of MitochondrionEM of Mitochondrion

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Evolution of MitochondrionEvolution of Mitochondrion

Evolved from bacteria that invaded primitive cell Evolved from bacteria that invaded primitive cell but was not destroyedbut was not destroyed

Double membrane formed from bacterial Double membrane formed from bacterial membrane and phagosomemembrane and phagosome

Has its own mtDNA Has its own mtDNA mutates readily causing degenerative diseasesmutates readily causing degenerative diseases

• mitochondrial myopathy and encephalomyopathymitochondrial myopathy and encephalomyopathy

Only maternal mitochondria inherited (from the Only maternal mitochondria inherited (from the egg)egg) sperm mitochondria usually destroyed inside eggsperm mitochondria usually destroyed inside egg

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CentriolesCentrioles

Short cylindrical assembly of microtubules (nine Short cylindrical assembly of microtubules (nine groups of three )groups of three )

Two perpendicular centrioles near nucleus form Two perpendicular centrioles near nucleus form an area called the centrosomean area called the centrosome role in cell divisionrole in cell division

Cilia formationCilia formation single centriole migrates to plasma membrane to form single centriole migrates to plasma membrane to form

basal body of cilia or flagellabasal body of cilia or flagella two microtubules of each triplet elongate to form the two microtubules of each triplet elongate to form the

nine pairs of the axoneme nine pairs of the axoneme cilium reaches full length rapidlycilium reaches full length rapidly

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CentriolesCentrioles

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CytoskeletonCytoskeleton

Collection of filaments and tubulesCollection of filaments and tubules provide support, organization and movement provide support, organization and movement

Composed ofComposed of microfilaments = actin microfilaments = actin

• form network on cytoplasmic side of plasma membrane form network on cytoplasmic side of plasma membrane called the membrane skeletoncalled the membrane skeleton

supports phospholipids and microvilli and produces cell supports phospholipids and microvilli and produces cell

movementmovement

intermediate fibersintermediate fibers• help hold epithelial cells together; resist stresses on cells; help hold epithelial cells together; resist stresses on cells;

line nuclear envelope; toughens hair and nailsline nuclear envelope; toughens hair and nails microtubulesmicrotubules

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MicrotubulesMicrotubules Cylinder of 13 parallel strands called protofilamentsCylinder of 13 parallel strands called protofilaments

(a long chain of globular protein called tubulin)(a long chain of globular protein called tubulin) Hold organelles in place; maintain cell shape; guide Hold organelles in place; maintain cell shape; guide

organelles inside cellorganelles inside cell Form axonemes of cilia and flagella, centrioles, basal Form axonemes of cilia and flagella, centrioles, basal

bodies and mitotic spindlebodies and mitotic spindle Can be disassembled and reassembledCan be disassembled and reassembled

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CytoskeletonCytoskeleton

7373

EM and Fluorescent Antibodies EM and Fluorescent Antibodies demonstrate Cytoskeletondemonstrate Cytoskeleton