Cytoplasm Final
Transcript of 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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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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S ll i l i l d
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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
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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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