cytoplasm final

8/14/2019 Cytoplasm Final

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By

Dr Iram Iqbal

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Cells are the basic structural and

functional unit of all multicellular

organisms. Cells can be divided into two

major components:

Cytoplasm

Nucleus.

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With the L/M, Cytoplasm

generally has an even,homogenous, amorphousappearance but may showgranular, fibrillar, or

vacuolated areas.Cytoplasm containsorganellesandinclusionsin aqueous

gel called cytoplasmicmatrix,

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Organelles are living,structural componentsof cell.

Organelles aredescribed as membranous (cell

membrane limited)

non membranous.

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1. Plasma (cell)membrane

2. rER

3. sER 4. Golgi apparatus

5. Endosomes

6. Lysosomes

7. Transport vesicles8. Mitochondria

9. Peroxisomes

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1. Microtubules

2. Filaments

3. Centrioles4. Ribosomes

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MEMBRANOUS ORGANELESMEMBRANOUS ORGANELES


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Plasma membrane is alipid bilayered structurethat form the cell boundary

as well as the boundaries ofmany organelles within thecell. It is visible with TEM.

It is a dynamic structure

that actively participates inmanyphysiologic andbiochemical activitiesessential to cell function andsurvival.

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When plasma membrane is

properly fixed, sectioned,

stained and viewed on edge with

TEM, it appears as two electrondense layers separated by an

intermediate, electron lucent

(non staining) layer.

Total thickness is about 8 10

nm.

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PROTIENS PHOSPHOLIPIDS

CHOLESTEROL

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Integralmembrane

proteins Peripheral

membraneproteins

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PRESENT ON ONESIDE OF

MEMBRANE

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Inserted inmembrane

Some entirelyextend throughmembrane

Perform many

importantfunctions

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Integral membrane proteins can be visualized with thespecial tissue preparation technique offreeze fracture.

Usually the P-face display more particles ,thusmore protein ,than the E-face.

E face

P-face


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Micro domains of plasma membrane known as lipid rafts

control the movement and distribution of proteins within lipid

bilayers.

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Localized regions with in the plasmamembrane contain high concentration ofcholesterol and glycosphingolipids.Theseregions are called lipid rafts.

Owing to high concentration ofcholesterol andthe presence of longer, highly saturated fattyacid chain, the lipid raft area is thicker andexhibits less fluidity than the plasmamembrane.

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Lipid rafts contain a verity ofintegral andperipheral membrane proteins involved incell signalling.

They can be viewed as signalling platforms floating in the ocean of lipids.

Signal transduction in lipid rafts occurs

more rapidly and efficiently because ofclose proximity of interacting proteins.

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Integral membrane proteins have important

functions in cell metabolism, regulation andintegration.

Six broad categories of membrane proteins have

been defined in terms of their function:1. Pumps

2. Channels

3. Receptor proteins

4. Linker proteins

5. Enzymes

6. Structural proteins

Integral membrane proteins move within lipid

bilayers of membrane

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TRANSPORT IONS serve totransport certain ions suchas Na + actively acrossmembrane.

Also transport metabolicprecursor ofmacromolecules, such assugar and amino acid across

membrane either bythemselves or linked throughNa+ pump.

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Allow Passage ofsmall ions and

molecules,andwater across theplasma membranein either direction

i.e ,passivediffusion

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For recognition and

binding of substances

to the outer surface of

plasma membrane

Like hormonal

stimulation and

antibody recognition

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Anchor theintracellularcytoskeleton to theextracellular

matrix.e.g,family ofintegrins that linkcytoplasmic actinfilament to a

extracellular matrixprotein

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Protineous

structures which

have specific roles

in ion pumping and

digestion

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Found in epithelialcells

Formjunctionalcomplexes withneighbouring cells

Visualized by

freeze fracturemethod.

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Carrierproteins

Channelproteins

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Some substances (fat-soluble and small uncharged molecules cross the plasmamembrane by simple diffusion down theirconcentration gradient.

All other molecules require membranetransport proteins to provide them withindividual passage across the plasma

membrane.

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Carrier proteins Channel proteins Transfer small water-

soluble molecules.

They are highly selectiveoften transporting only onetype of molecules.

After binding to a moleculedesignated for transport,the carrier proteinundergoes a series of

conformational changesand releases the moleculeson the other side of themembrane.

Also transfer small,water solublemolecules. Channel

proteins createhydrophilic channelsthrough the plasmamembrane thatregulate the transport

of the molecules.They are ion selective

and are regulated onthe basis of the cell'sneeds

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VESICULAR TRANSPORTprocess that

involves configurational changes in the

plasma membrane & also provides for the

transfer of molecules b/w different cellularcompartments

It maintains the integrity of plasma

membrane

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EXOCYTOSIS ENDOCYTOSIS

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Processes of vesiculartransport in whichsubstances

enter the cell aretermed as endocytosis

Uptake of fluid andmacromolecules during

endocytosis dependson three differentmechanisms

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PHAGOCYTOSIS

PINOCYTOSIS RECEPTOR MEDIATED

ENDCYTOSIS

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PHAGOCYTOSIS Also called cell eating It is ingestion of

large particles, such

as cell debris,bacteria and otherforeign materials

In this nonselectiveprocess large

vesicles(250nm)called phagosomesare produced

Best seen in

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PINOCYTOSIS Also called cell

drinking Is the nonspecific

ingestion of fluidand small proteinmolecules via small

vesicles usuallyamaller than150nmin diameter.

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This is areceptormediatedmechanismthat allowsselectedmolecules toenter the cell.

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IMG Code

more

http://med

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Exocytosis is the processby which a vesicle moves

from the cytoplasm to the

plasma membrane,where

it discharges its contents tothe extra cellular space.

Two general pathways of

exocytosis:

Constitutive pathway

Regulated secretory pathway

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These are the membraneenclosed compartments inthe cytoplasm, associated

with all the endocytoticpathways Endosomes can be

viewed either as stablecytoplasmic organelles or

as transient structuresformed as the result ofendocytosis.

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Endosomes destined tobecome lysosomesreceive newlysynthesized lysosomalenzymes

Early and lateendosomes differin theircellular localization,

morphology and state ofacidification andfunction.

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Early endosomes are restricted to portion of

cytoplasm near the cell membrane wherevesicles originating from the cell membranefuse.

Large number of vesicles originating in

early endosome travell to deeper structuresin the cytoplasm called late endosomes.

The late endosomes mature into lysosomes.

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Major function of earlyendosomes is to sort andrecycle proteins

internalized byendocytotic pathways.

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Early endosomes Late endosomes

Found in moreperipheral cytoplasm

Have a tubovesicularstructure.

Lumen is subdivided into cisternae PH 6.2 - 6.5

Found near the Golgiapparatus and thenucleus.

More complex structureand often exhibit

onionlike internalmembrane.

PH 5.5

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Lysosomes are smallmembrane boundorganelles that contain avariety of acid hydrolases.

Ribosomes are composedof two different sizedsubunits.

The RNA molecules of

both subunits aresynthesized in side thenucleus.


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Their numerous proteins are synthesized in the

cytoplasm and then enter the nucleus and associate

with rRNA .

Subunits then leave the nucleus via nuclear pores, to

enter the cytoplasm and participate in protein synthesis.

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They constitute anintracellular digestivesystem capable of breaking

down material originatingboth outside and within thecell.

Great variety ofappearances or

pleomorphism.

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Usually range from 0.2 0.4

um in diameter. Have a unique membrane that is

resistant to hydrolytic digestionoccurring in their lumen.

Lysosomal membrane has anunusual phospholipid structurethat contain cholesterol and aunique lipid called lyso-

phosphatidic acid which play an

important role in restricting theactivity of hydrolytic enzymesdirected against the membrane.

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Found in all cells excepterythrocytes but arenumerous particularly

in:Macrophages

Neutrophils

Hepatic cells

Cells of Proximal tubuleof kidney

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Identified by

Electron

cytochemistry Divided into main

groups:1.Primary lysosomes2.Secondary lysosomes

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Newly formedlysosomes that havepinched of from

golgi cisternae Contain all enzymes

that are used in celldigestion

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Formed by fusion ofprimary lysosomeswith the structurethat contains materialto be digested

Also called

phagosome.digestivevacuole orautophagic vacuole

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Hydrolytic breakdown of the contents of thelisosomes often produced a debris-likedvacule called a Residual body.which mayremain for the entire life eg residual bodies

are a normal feature of the cell aging

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Normal feature ofcell aging

Debris filled vacuole

Produced by breakdown of contents ofsecondary lysosomes

Found as age pigmentor lipofusin pigment

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Depending on the nature of digested material, threedifferent pathways deliver material for intracellular

digestion in lysosomes:

1.Extra cellular large particles .. Phagosome and

Phagolysosome.

2.Extra cellular small particles ..Endocytotic pathway.

3.Intracellular particles .. autophagy

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With TEM, RERappears as a series ofinterconnected,

membrane limitedflattened sacs calledcisternae, with particlesstudding the external

surface of membrane(ribosomes).

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Basophilic component of cytoplasm,


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p p y p

ergastoplasm-----the areas of cytoplasm that stain

blue with basic stains

. Ergastoplasm indicates i.e. that component ofcytoplasm involved in protein synthesis..


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Protein synthesis systemof the cell consists ofrERand ribosomes

The particles calledribosomes are attachedto the membrane ofeRE by ribosomaldocking proteins

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Membrane of reticulumenclose an intracellularcompartment thatsegregates newlysynthesized products.

Its main function issynthesis of a secretory

protein

Synthesis ofphospholipids Glycosylation of

glycoprotiens

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On E/M, appear as small, dense particles of about

15 20 nm in diameter, roughly spherical but

irregular, and each is formed by two subunits, one

large and one small.

Responsible forcytoplasmic basophilia and they

contain RNA andprotein.Are sites where amino acids are incorporated into

peptides and proteins i.e. site of protein synthesis

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Found in all cells except mature erythrocytes.

May be attached to granular endoplasmic reticulum

or may lie free within general cytoplasm.

Polysomes or polyribosomes----a cluster ofribosomes along a single strand of mRNA that is

engaged in the synthesis of protein.

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Ribosomes are the sites where mRNA is translated

into protein.

Proteins destined fortransport (secretory,membrane, and lysosomal) are synthesized on

polyribosomes bound to rER .

whereas proteins not destined for transport (for

intracellular use) are synthesized on free

polyribosomes in cytosol.

Ribosomes are numerous in rapidly growing and

dividing cells.

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SER is an irregularnetwork of membrane

bounded channels that

lacks ribosomes on itssurface, which makes itappear smooth.

SER consists ofshort

anastomosing tubules

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Membranes are 6 7 nmthick, and a tubular lumenof about 50 nm.

May exhibit distinctcytoplasmic eosinophilia.

Tubular elements mayconnect directly with rERand indirectly with golgiapparatus via smallvesicles.

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Cells with large

amount of SER may

exhibit distinctcytoplasmic

eosinophiliawhen

viewed under L/M.

Biochemically similarto RER but lacks

ribosome docking

proteins


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Abundant in cells that function in lipid metabolism,

cells that synthesize and secrete steroids (e.g.adrenocortical cells and testicular cells of leydig,progesterone secreting cells of corpus luteum ofovary).

Lipid and steroid metabolism Glycogen metabolism Membrane formation and recycling Synthesis of phospholipids of all cell membrane Drug detoxification Muscle contraction and relaxation (specialized

form,sarcoplasmic reticulum)

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Well developed in secretory cells and does notstain with H & E.

May be visible by L/M as either a positive ornegative imageAfter routine H & E stains, in cells with intensely

basophilic cytoplasm such as osteoblasts &

plasma cells, golgi apparatus is indicated as apale, clear area. This is negative imageAfter silver impregnation or prolonged exposureto osmium tetra oxide, it is seen as darkly stainingnetworkof stacked, flattened, membrane limitedsacs orcisternae and tubular extensions embeddedin a networkof microtubules near MTOC-----Positive image

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Small vesicles involved

in vesicular transport

are seen in associated

with cisternae.

Regions:

Cis golgi network

(CGN)Trans golgi network

(TGN)

Medial golgi


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It is active in cells:

That secrete protein by exocytosis

In cells that synthesize large amounts of membrane andmembrane associated proteins such as nerve cells.

It functions in post translational modification,

storing andpackaging of proteins.

It is involved in membrane flow , in transport andconcentration of secretory materials and their

release from the cells, in synthesis of certain

secretory products, particularly glycoproteins and

mucopolysacchrides and probably in lysosome

formation

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Basolateralplasmamembrane

Apical plasma

membrane Endosomes or

Lysosomes

Apical

cytoplasm

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Are membrane boundorganelles and lie free

within cytoplasm. Display avariety of shapes includingspheres, rods, elongatedfilaments and even coiledstructures.

Present in all cells exceptRBSs and terminalkeratinocytes

Abundant in cells that

generate large amounts ofenergy.

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Each mitochondria isbounded by two unitmembranes

Inner membrane showsfolds called cristae toincrease the surface area

The space b/w inner andouter membrane iscontinuous with theinterstitial space withineach crista

The inner mitochondrialmembrane surrounds thelarge intercristal space ofmitochondrial matrix.

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Outer mitochondrialmembrane 6 7 nm thick smooth

membrane Contains many anion

channels

Possess receptors forproteins andpolypeptides

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Inner mitochondrialmembraneThinnerthan outer oneArranged in cristaeRich inphospholipids

Cardiolipin, which makes themembrane impermeable toionsThe internal membrane andcristae are coated with smallparticles called elementary

particles orglobular units

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These have special heads 9-10 nm in diameter

attached to inner mitochondrial membrane by a

narrow 5nm long stalk

Enzymes ofphosphorylation and electron transfer

system are located either on elementary particles

or within the inner mitochondrial membrane that

form cristae

Enzymes ofKreb,s cycle lies in mitochondrial matrix

The matrix also contain calcium salts, organic

crystals, glycogen, and RNA, DNA,

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1. Performing the oxidative reactions of therespiratory electron transport chain

2. Synthesizing ATP3. Regulating transport of metabolites into

and out of the metrix.

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Intermembranousspace

Contain specific

enzymes that use ATPgenerated in innermitochondrialmembrane (e.g.creatine kinase,adenylate kinase andcytochrome C)

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Store house for energy, metaboliteswithin the cell are utilized by Kreb,scitric acid cycle and energy released is

captured through oxidativephosphorylation. thus ATPs are formedwhich are high energy compound.

Involved in fatty acid B oxidation.

Source ofelectron for electron

transport chainStore Ca++ and other divalent andtrivalent cations.

Synthesis ofsteroid hormons

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Small (0.5 m in dia.)membrane boundedspherical organelles

containing oxidativeenzymes (particularlycatalases and otherperoxidases)

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Abundant in liverand kidney cells,but found in most

other cells Do not contain

hydrolases

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Oxidative enzymes areperform a variety of

detoxification

processes. oxidation of fatly

acids is also a majorfunction of

peroxisosomes

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These are nonbranchingand rigid hollow tubes

of proteinthat can rapidly disassemble in one

location and reassemble in another.

In general, they grow from MTOC located nearnucleus and extend toward the cell periphery.

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The region of the cell containing thecentrioles and pericentriolar material iscalled MTOC or Centrosome.

The MTOC is the region where most

microtubules are formed and from whichthey are directed to specific destinationswithin the cell.

The structures present in MTOC are cilia,

basal bodies and centrosomes

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Development of MTOC itself depend onpresence ofcentrioles.

When centrioles are missing MTOCsdisappear ,and formation of microtubules is

severely impaired.

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Complex structureof tubulin

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These are elongated polymeric structures


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composed of equal parts of tubulinand tubulin.Under appropriate conditions tubulinsubunits polimerize to formmicrotubules

Microtubulesgrow from tubulin ringwithin the MTOC that serve asnucleation sites for each microtubule.

Each microtubule possesses a minus(non-growing) endand aplus (growing)end.

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Polymerization and depolymerization are

in equilibrium.

Length of microtubules changes

dynamically as tubulin dimers are added or

removed in a process of dynamic

instability.

These can be visualized in L/M and are

involved in intracellular transport and cell

motility

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The figure shows the 3-dimensional

view of a microtubule being formed. Thetubulin molecules are the bead likestructures and combine to form longhollow, dynamic polymers, microtubules

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In general, microtubules are found in:

Cytoplasm (where they originate from MTOC)

Cilia and flagella(where they form axoneme and its

anchoring basal body).

Centrioles and mitotic spindle.

Elongation processes of cells(such as those in growing

axons)

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Microtubules are involved in numerous essential


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Microtubules are involved in numerous essential

cellularfunctions:

Intracellular vesicular transportAttachment of chromosomes to the

mitotic spindle and their movement

during mitosis and meioses.Cell elongation and movement.

Maintenance of cell shape, particularly

its asymmetry.

Movement of cilia and flagella

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Movement of intracellular organelles is

generated by molecular motor proteins(associated with microtubules)Dyneins

Kinesins

Both dyneinsand kinesins are involved inmitosis and meiosis. In these activities,

dyneinsmove the chromosome along the

microtubules of the mitotic spindle.Kinesinsare simultaneously involved in

movement of polar microtubule.

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Present in virtually all celltypes.

Abundant and may constitute20% of total protein of somenon muscle cells.

Similar to tubulin in

microtubules actin moleculesalso assemble spontaneously

by polymerization into alinear helical array to formfilaments 6 8 nm in

diameter. Thinner, shorterand more

flexible than microtubules.

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G actin (globular actin),free actin molecule in the

t l


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cytoplasm

F actin (filamentous actin) polymerized actin of

the filamentPlus or barbed end,fast growing end

Minus or pointed end. slow growing end

Polymerization of actin filaments requires K+, Mg2+,

ATP

Control and regulation of polymerization process

depends on:

Local concentration of G actinInteraction ofactin binding proteins (ABPs)

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Anchorage and movement of membraneprotein

Formation of the structural core of

microvilliLocomotion of cells

Extension of cell processes

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Play a supporting orgeneral structural role.

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Intermediate

filaments are

formed from non

polar and highly

variable

intermediatefilament subunits


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These rope like

filaments are called

intermediate becausetheir diameter is 8 10

nm (intermediate

between actin filaments

and microtubules).

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Characterized by a highly

variable central rod shapeddomain with strictlyconserved globular domainsat either end.

Although various classes of

intermediate filaments differin the amino acid sequenceof rod shaped domain andmay show variation inmolecular weight, they all

share a homogenous regionthat is important in filamentself assembly.

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Usually found in close

proximity to thenucleus, partially

surrounded by golgi

apparatus and

associated with a

zone of amorphous,

dense pericentriolar

material

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Centrioles represent the

focal point around which

the MTOC assembles.

Visible in L/M, arepaired short, rod like

cytoplasmic cylinders

built from nine

microtubule triplets.

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Arranged at right

angle to each other

but are not

connected with one

another

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The dominant feature of

centrioles is the cylindricalarray of triplet microtubuleswith associated proteins.

TEM reveals that each rod

shaped centriole is about 0.2m long and consists ofninetriplets of microtubules thatare orientedparallel to the

long axis of organelle andrun in slightly twistedbundles.

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Functions ofthecentrioles can beorganized into

two catagories. Basal body

formation

Mitotic spindle

formation


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The core structure of

the cilium is composed

of a complex set of

microtubules consisting

oftwo central

microtubules

surrounded by ninemicrotubules doublets.

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One of the important function ot the centriole is toprovide basal body. Which are necessary for theassembly of cilia and flagella.

Basal bodies are formed by the replication ofcentrioles and give rise to multiple precentrioles . Each precentriole migrate to appropriate site on

the surface of the cell where it become a basalbody.

The basal body act as a organizing center forcilium

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Microtubules grow upward from the basalbody,pushing the cell membraneoutward,and alongated to form themature cilium.

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Inclusions contain products of

metabolic activity of the cell

and consist largely ofpigment

granules, lipid droplets and

glycogen. Lipofuscin

Hemosiderin

Glycogen

Lipid inclusions (fat droplets)

Crystalline inclusions

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Lipofuscin, is con glo me rate of lipid,metalsand organic molecules that accumulate within


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the cell as a result of oxidative degradation ofmitochondria and lysosomal digestion.

Hemosiderin , it is most likely formed by theindigestible residues of hemoglobin,and its

presence is related to phagocytosis of RBCs.

Glycogen, is highly branched polymer usedas a storage material for glucose.

Fat droplets, are nutritive inclusion thatprovide energy for cellular metabolism.

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Hemosiderin inside macrophages


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Glycogen in liver cells

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Lipid droplets


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They aresurrounded bymembrane

Usually present inapical portion ofcell

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A concentrated aqueous solution containingmolecules of different sizes and shape( e.g,electrolytes, metabolites ,RNA andsynthesized proteins)

The cytoplasm matrix is the site ofphysiological processes that arefundamental to cell's existence (proteinsynthesis, breakdown of nutrients)

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The network provides a structuralsubstratum on which cytoplasmic reactionsoccur.

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Text and Atlas of Histology by Michael H. Ross, 5th

edition.

Text book of Histology by Leeson Leeson Paparo, 5th

edition.

Image Results --------www.google.com

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