The document provides information about cell structure and organelles. It discusses that the cell is the basic structural and functional unit of life, and can be unicellular or multicellular. It describes eukaryotic and prokaryotic cells, and notes that human cells fall under the category of eukaryotic cells. The document then focuses on cell membrane structure, including the fluid mosaic model. It discusses various cell organelles like mitochondria, endoplasmic reticulum, Golgi apparatus, and lysosomes and their structure and functions.

1. CELL
Department of Physiology
NIMT
SANJOG BAM

2. Introduction
• Cell is the structural and functional unit of the life.
• Presence of cell wall in plant kingdom.
• Multi cellular and unicellular organism.
• Unicellular: amoeba, plasmodium, Bacteria, viruses , yeast (fungi
kingdom)etc
• Prokaryotic cells: protozoa, paramecium, bacteria, virus etc[histone is not present in DNA,
no mitosis & meiosis]
• Eukaryotic cell: euglena, mammal cells, fungi, plant kingdom, all warm and cold bodies
animal etc
• Multicellular:
– vertebrates (mammals, reptiles, birds, amphibian, pisces etc)
– invertebrates all cold bodies organism.
• We human {Homo sapiens} falls under mammals.
• In human body cells are well organized so, that we can earn our livelihood.
• Cells ultimately lead to form the system, hence due different system’s
peculiar coordination makes human body.
• Within human body, there are different kinds of cells classified.
• Reproductive cells and somatic/vegetative cells
• Within somatic cells again we can classify on the basis of different things like
blood cells, bone cells , cell for vision, hair cells, skin cells etc

3. Multicellular
Euglena, unicellular
Eukaryotic cell structure

4. • Cell consist membrane like structure covering fluid in
them
• Membrane is the plasma membrane/cell membrane
and it contains fluid with different cell organelles.
• Cell membrane is one of the biomembranes.
• Cell membrane is the phospholipid bilayer consisting
proteins, lipid, carbohydartes, cholestrol.
• The hydrophobic effect and solvent entropy provide
the driving force for the formation of lipidbilayer.
• Two models were mention:
– Sandwitch model
– Fluid mosaic model

5. The Davson–Danielli (1935) model predominated until Singer and
Nicolson advanced the fluid mosaic model in 1972.

6. Fluid mosaic model
• Looks like ice berg of proteins, lipid, carbohydrate, cholesterol, floating on the sea
of phospholipid.
• It’s the dynamic structure.
• Fluidity in nature, cholesterol:phospholipid determines the fluidity of the
membrane.
• The degree of unsaturation determines the fluidity of the membrane.
• Within the plane of the membrane, one molecule of phospholipid can move
several µm per second.
• Hydrophobic tails i.e lipid aligned facing towards each other.
• Hydrophilic phosphate head facing towards ECF(Extracellular fluid) compartment
and ICF(Intracellular fluid) compartment.
• 7-10 nm in thickness
• Protein:
– Integral protein
– Peripheral protein
• Extrinsic protein
• Intrinsic protein

7. Effect of temperature
• In membrane, fatty acids chains highly aligned or ordered
to provide a rather stiff structure.
• As the temperature increases, hydrophobic side chains
undergo a transition from the ordered state which is more
like gel or crystalline to a disordered state, taking on a more
liquid like or fluid arrangement.
• The temperature at which the structure undergoes the
transition from order to disordered(melts) is called the
transient temperature.
• As fluidity increases, the lateral mobility of integral protein
also increases.
• Membrane consist at least one unsaturated fatty acid with
at least one cis bond.

8. Additional special features of some
membrane.
• The following two structure which currently drawn
attention are:
– Lipid rafts:
• They are dynamic areas of the exoplasmic leaflet of the lipid bilayers
enriches in cholesterol and sphingolipids.
• They are involved in signal transduction and possibly other processes
– Caveolae:
• Derived from lipid rafts.
• Many of the caveolae contain special protein called caveolin-1.
• By electron miscroscope, they look like flask-shaped indentations of
the cell membranes.
• Also takes part in signal transduction
• Protein detected in caveolae include various components of signalling
system e.g: the insulin receptor and G-proteins, folate receptor and
endothelial nitric oxide synthase(eNOS).

9. Special characteristics of RBCs
membrane
• Integral proteins: two major integral proteins
– Glycophorin:
• Glycoproteins(oligosaacchrides)
• 60% carbohydrate by weight
• The oligosaccharides bound to glycophorin are linked to serine, threonine and
aspargine residues.
• 130 amino acid residues.
• One RBC consist about 6 *10^5 glycophorin molecule
• Some of the oligosaccarides of glycophorins are the M and N blood group
antigen.
• Other carbohydrates of glycophorin are the sites for influenza virus attachment.
– Band 3 protein
• Dimeric, 93000MW, polypeptide chain of the dimer is thought to traverse about
dozen time.
• Bothe C and N terminals of protein are towards cystolic side of the membrane.
• N-terminal residues extend into the cytosol and interact with components of the
cytoskeleton
• While blood going through lungs ,this proteins act as bicarbonate ion/ chloride
ion exchanger; bicarbonate ion outside.

10. Peripheral of RBCs membrane
• The inner face of the RBC membranes is laced with a network of
proteins called cytoskeleton that stablizes the membrane, hence
resulting biconcave shape. Daimeter:7-8µm
• Peripheral proteins for stability of RBC:
– Spectrin
• Α α chain(240,000 MW) &β(220,000MW). dimer
• Fibrous protein where these chains are twisted/coiled with each other. 100nm
long & 5nm breadth
• These dimers are linked through short chains of actin molecule and band 4, 1
proteins to form tetramer(2α & 2β) polypeptides.
– Actin
• In RBC and other non muscular cells, it is the component of cytoskeleton.
• Consist 5*10^5 molecules per RBC
• Only 20 actin molecules polymerise to form short actin filament.
– Ankyrin and Band 4, 1 proteins
• In network none of above proteins including band4 &1 are directly attached to
membrane.
• That network of proteins is instead attached with ankyrin(MW 200,000), Two
domains.
• One binds with spectrin and other N terminal region of band-3

12. Hereditary spherocytosis and hereditary
elliptocytosis.
• Inherited genetic abnormalities of rbc
• Abnormal shape
• Spherical in spherocytosis & ellipsoidal in
elliptocytosis.
• Increase osmotic fragilty, increase hemolysis,
anemia and jaundice
• Due to mutation in the genes coding proteins of
the membrane.
• Increament in mean corpusles volume(MCV).

13. Integral protein
• Also called trans-membrane protein.
• Act as the ion channels & other things ions
pump
• Channels for polar substrate.
• Act as the receptor and enzymes.
• Act as the carrier protein.
• Antigenic function. Blood group antigens.

14. Membrane carbohydrates
• In glycocalyx, Oligosaccharides that are covalently linked to
membrane proteins to form glycoproteins or lipid forming
glycolipids.
• Glycocalyx loosely covers external membrane surface, serves as
protective coat.
• Due to negativity of carbohydrates, negative particles like protein
molecule from another cells gets repelled.
• Some trans-membrane glycoproteins like selectin recognize and
bind with specific oligosaccrides of other cells, temprorary cell-to-
cell adhesion.
• Such temporary adhesion occurs between neutrophils and
endothelial cells at the site of inflammations.
• Strong cell adhesion is formed by integral proteins i.e integrin
• Some carbohydrates molecule serves as a receptor.

15. Peripheral proteins
• Intrinsic protein:
– Serves as enzymes
– Anchor proteins for cytoskeleton and other
microfilaments that maintain cell shape.
• Extrinsic protein:
– cell adhesion molecule(CAMs)
– Anchor with other cells and basal lamina
– They can be removed with disrupting the
membrane.

16. Function of cell membrane
• Maintains a constant and distinctive
intracellular environment, act as barrier,
semipermeable membrane.
• Maintains cell volume.
• In neurons and muscles cells, maintains the
potential gradient between ECF and ICF.
• Helps in recognizing foreign cells or antigens
so that they can be destroyed or phagocytes.

17. Permeability of membrane
• Selective permeability

18. Cell organelles
• Mitochondria:
– Power house of the cell.
– Consist their own genetic material.
– More in liver, cardiac cells and other that have high rate of metabolism
– Structure: membrane, cristae
– Double layer membrane:
• Outer membrane:
– continuous envelope of organelle
– Consists mostly phospholipid and cholesterol and specific protein
“porin”
– Porins makes the channels that permits substance to cross if it is MW
is less than 10,000
• Innermembrane:
– Rich in proteins, lipid: protein ratio 0.27:1., hence it is virtually
impermeable to polar and ionic substance.
– Inner membrane is folded into multiple in complete septa like
structures called cristae.
– Cristae is rich in many enzymes: cytochromes b, c1, c, a and a3,
succinate dehydrogenase, NADH dehyrogenase, electron transfering
flavo proteins, carnitine-palmitoyal transferase etc
– No. of cristae is more in resting condition and decreases in the
respiring state.

19. Mitochondrial matrix
• Enclosed by the inner membrane
• Amorphous materials fills the matrix, which
contains enzymes involved in the kreb’s critic
cycle and β-oxidation.
• Also contains several strands of DNA and also
the ribosomes and enzymes for synthesis of
proteins coded in the mitochondrial genome.

20. Functions of mitochondria
• The inner membrane contains the cytochromes of the ETC,
and associated enzymes for oxidative phosphorylation.
• Formation of ATP by ATP synthase from FADH2, NADH,
through complex five in ETC system.
• Like most components of the cell, mitochondria also has the
short life span like other organelles and are constantly
renewed.
• As they have strands of DNA, they are capable of self
replication & can make their own protein synthesis.
• mitochondrial DNA (mt DNA) has a higher rate of mutation
and less efficient repair machinery compared to nuclear
DNA.
• With advanced age, mitochondrial DNA volume, integrity and
functionality decrease due to accumulation of mutations and
oxidative damage induced by reactive oxygen species (ROS).

21. Anomalies of mitochondria
• The disease that affects mitochondrial energy
transduction is called Luft’s disease.
• The abnormality of mitochondrial genome leads to
cellular dysfunction which is manifested:
– Muscles weakness
– Degenerative lesion of brain
– High level lactic acid in blood
• Mitochondria is also affected by free radicals and in
age related degeneration.
• The oxidative stress theory of aging proposes that
mitochondria play key roles in aging by generating
reactive oxygen species (ROS)

22. Endoplasmic reticulum
• Consists of a network of anastomosing membranous
tubules, vesicles, and flattened cisternae.
• Membrane of ER is continuous with the nuclear
membrane and also connected with the Golgi
apparatus.
• Site for protein, lipid synthesis for the membrane of
the cell, organelles and secretory vesicles of the
cytoplasm.
• There are two type of ER:
– Rough ER
– Smooth ER

23. Rough ER
• Surface of ER is studded with
ribosomes.
• Granular appearance.
• In some cells like RBC, the ribosomes
lies freely in the cytoplasm.
• RER present more no. in cells which
actively involved in protein synthesis
like acinar cells of pancreases, hepatic
cells, neurons etc.
• In neurons, the Nissl granules are
modified RER
• Abundant in endocrine glands & cells
secreting digestive enzymes.
• Helps in conjugation of carbohydrates
with proteins to form glycoproteins, a
function which it shares with golgi
apparatus.

24. Smooth ER
• Ribosomes not attached or the
agranular ER.
• Concerned with lipid synthesis,
hence abundant in cells that
synthesize cholesterol, steroid
hormones and phospholipids.
• In muscles, known as sarcoplasmic
reticulum(storage of calcium ions),
these calcium released during
muscular relaxation cycle.
• Part of intracellular transport
system as it is continuous with RER
and golgi apparatus
• Site for detoxification &
neutralization of hormones and
toxic substances.

25. Golgi apparatus/golgi
complex/Dicytosomes
• Contains the unique stack of smooth surfaced compartments or cisternae that make up the Golgi
complex.
• The ER is usually and closely associate with Golgi complexes, which contain flattened , fluid filled Golgi
sacs.
• Each golgi complex has the proximal or Cis or a medial compartment and distal or trans or lateral
compartment.
• Cis /proximal is for receveing peptides newly synthesized in ER , via transfer vesicles..
• Post-translation modification of the proteins takes place in the Golgi lumen between cis & trans
compartment which involves covalent attachment including glycosylation, phosphorylation etc
• Recent evidence suggests strongly that the complex server as unique sorting device that recevies newly
synthesized proteins, all containing signal or transit peptides from RER.
• It is interesting to note that those proteins with no signal or trans peptides are automatically rejected ,
further those peptides remains as the cytoplasmic proteins.
• Packaging of the proteins and primary lysosomes(synthesize in RER), modification of enzymes.
• In the tra ns/ distal, they release proteins via modified membranes called secretory vesicles like
neurotransmitter vesicles in neuron, peptide enzymes containing vesicles. these formed vesicles also of
three types known till now.
– Small clear vesicles : acetyl choline
– Large clear vesicles: catecholamines,steriod hormones
– Large dense vesicles: peptide hormones
• Lysosomal enzymes are formed in Golgi complex.

26. Lysosomes
• large irregular structure, single membrane bound spherical
organelles that contain a variety of hydrolytic enzymes
meant for intracellular cytoplasmic for digestion.
• 250-750µm in diameter,
• More than 40 different lysosomal enzymes (lysozymes)
have been isolated.
• Interior of pH near 5, acidic due to proton ATPase pump.
• Lysosomes are found in almost all cell except RBC, where as
it is abundant in neutrophils and macrophages.
• Acid phosphatase , marker for lysosomal activity in tissue.
• In granulocytes, lysosomes appear as cytoplasmic granules.
• In death of the cells, lysosomal bodies disintegrate
releasing hydrolytic enzymes in cytoplasm , due to this cell
undergoes autolysis. There fore it is also called “suicidal
bags.”

27. Types of lysosomes
Lysosomes
-Primary lysosome
-Golgi hydrolase vesicles
-Referred as Storage vacuoles
Secondary lysosomes
- These lysosomes fused with
endosomes(like phagosome),
hence called endolysomes.
Tertiary lysosome
(phagolysosomes/
autophagosomes)
- formed by fusion of
phagocytic vacoules
with primary lysosomes
Newly formed
-enzymes inactive stage
Primary lysosomes fused with
Endosomes.
Enzymes are active.
Contains degraded product
after phagocytosis
-NO enzymatic activity

28. • During the process of phagocytosis, the
phagosome formed through cytoplasmic
pseudopodia containing foreign bodies,
further it gets fused with primary lysosomes
forming phagolysosome.
• Lysosomal enymes later digest the foreign
particles, there for lysosomes are known as
autophagosomes.

29. Function of lysosomes
• Acts as a digestives system of the cell.
• Help in phagocytosis.
• Engulf worn out components of the cell.
• Acts as suicidal bag/ autolysis.
• Acrosome, located on the head of the
spermatozoa is the specialized lysosomes,
with hydrolytic enzymes activity acrosomes
helps in penetration of ovum by sperm.

30. Lysosomal enzymes
• Proteolytic enzymes:
 Cathepsins(proteinase)
 Collagenase
 Elastase
• Nucleic acid hydrolyzing enzymes:
 Ribonucleases
 dioxyribonuclease
• Lipid hydrolysing enzymes:
 Lipases
 Phospholipases
 Fatty acyl esterase
• Carbohydrates splitting enzymes:
 α-glucosidase
 Β-galastosidase
 Hyaluronidase
 Aryl sulphatase etc
• Other enzymes:
 Acid phosphatase(marker)
 Catalase( anto oxidant enzymes) etc

31. Clinical related to lysosomes
• In gout, urate crystals are phagocytosed by
lysosomes which were deposited on the joint
,mostly toes joint. Crystal cause physical
damage to lysosomes, causing release of
enzymes producing inflammations and
arthrites.

32. Peroxisomes
• Similar to that of lysosomes but different chemical composition.
• Small spherical organelles, about 0.5µm diameter, also denoted as
microbodies.
• Formed through budding or division of SER.
• Referred as subcellular respiratory organelles. But they don’t have
energy coupled ETC system.
• It contains oxidases (enzymes producing H2O2), which promotes
lipid peroxidation( long chain fatty acid) forming acetyl coA &H2O2,
rather than hydrolase.
• Catalase that liberates oxygen from H2O2, thus protects tissue from
oxidative stress (OS). Hence , increased catalase activity is one of
the marker of OS
• They consume small amount oxygen, but its not for ATP formation.
• They carry out oxidation reactions in which toxic hydrogen peroxide
is formed, which is destroyed by the catalase.
• With the help of peroxins, the protein chaperons, various proteins
with specific signals are directed to peroxisomes
• The alcohol, a person drinks is mainly detoxified by the peroxisomes
of the liver cells.

33. • The enzyme AGAT[alanine glycoxalic acid transferase] is only found in
peroxisome, which catalysis the formation glycoxalic acid from glycine,
along with transformation of pyruvate to alanine[amino tranformation
rexn]
• Recently, it has been shown that hepatic peroxisomes have an unusually
active β-oxidative systems capable of oxidising long chain fatty acids (C16
to ≥C18).
• Oxidation first step is unique as it is catalyzed by a flavo protein, an acyl
Co-A oxidase.

34. Clinical related to peroxisomes
• Zellweger syndrome:
– Mutation of genes coding for peroxins or peroxisomal
enzymes.
– Neurological impairment, accumulation of very long chain
fatty acids(VLCFA)
– Abnormalities in synthesis of bile acids and marked
reduction of plasmalogens.
– Child usually dies within a year
• Brown-Schilder’s diseases:
– Insufficient oxidation of VLCFA by peroxisomes.
– Autosomal recessive diseases manifest with progressive
degeneration of liver, kidney and brain.
• Primary hyperoxaluria:
– Defective peroxisomal metabolism of glycosylate derived
from glycine.

35. Nucleus
• Contains more than 95% of the cell’s DNA and is the control
centre of the eukaryotic cell. Site for DNA replication and
RNA transcription of DNA
– Nuclear envelope
• double membrane structure, separates the nucleus from the cytosol.
– Nuclear pore complexes
• Embedded in the nuclear envelope
• Controls the movement of proteins and RNAs into cytoplasm
– Chromatin
• Dense mass of the coiled DNA
• Stained darkly with certain dyes
– Nucleolus
• Second dense mass closely associated with the inner envelope
• Non-membranous and consists RNA polymerases, RNAase, ATPase and
other , but not DNA polymerase
• Major site where ribosome subunits assembled
• Site of synthesis of ribosomal RNA (r-RNA)
– Nucleoplasm
• Cytosol of nucleus
• Contains various enzymes such as DNA polymerases, and RNA
polymerases, for m-RNA and t-RNA synthesis.

36. Centrioles or centrosome
• Centrosomes is formed from two centrioles.
• These are short cylinder called “centrioles”, which are visible during
cell division.
• They are located at each pole near the nucleus and are so arranged
such that they are at right angles to each other within amorphous
pericentrioles material.
• Tubules in group of three(triplets) run longitudinally in the walls of
the centrioles, through which chromosomes movement takes place.
• There are nine of these triplets spaced at regular intervals around
the circumference.
• The subunits of microtubules in centrosome are Ꝩ-tubulins.
• Centrosomes are microtubule-organizing centre (MTOCs)
• Regulate chromosomes during cell division.
• Centrosomes duplicate themselves and move toward opposite pole
(mitotic spindles) to monitor process during the cell division

37. Cross-section of
centrosome.

38. CYTOSKELETON
• From many years, biochemist have considered the
cytosol a compartment containing soluble enzymes,
metabolites and salts in an aqueous but gel like
environment.
• It allows the cell to change their shape and permits its
movement.
• Studies now supports the idea that this compartment
contains actually a complex network fine structures
mention below:
• Microtubules
• Microfilament
• Intermediate filament

39. CYTOSKELETON
• Microtubules:
– Long hollow structure, approx. 25 nm in diameter including the wall
of thickness.
– Inner cavity diameter of microtubule is around 15nm.
– the structures are made primarily by self assembly of the
heterodimers, tubulin having MW:50000 & interaction with GTP
facilitates microtubule formations.
– Tubulin is a globular protein have two subunit.α & β tubulin closely
packed in the helical manner. Except tubulin in centrioles has Ꝩ-
tubulin.
– α & β tubulin subunits forms heterodimer that aggregate to make the
tubular structure or protofilament of stacked ring.
– Each stacked ring in microtubule usually contains 13 protofilaments.

40. • Tubulin subunits has one unique property of disassembly and assembly, hence microtubules
forms the dynamic cytoskeletal framework of the cell.
• Microtubules are polar in nature, with assembly predominating “+ve” end disassembly
predominant “–ve” end, and also are heat liable or sensitive with cold condition favouring
disassembly.
• The structure or tracts on which chromosomes, mitochondria and secretion granules move
from of the one site to another site within the cell.
• In cell with cilia and flagella, microtubules extend into these structure.
• Kinesin and dynein are microtubules-based motor molecules or acts as the cargo.
• Role in assembly and disassembly of the spindles that move chromosomes during during
mitosis.
 Also provide internal structure to the sell and helps in maintenance of shape of the
RBC.
 As they seems to associate with the inner face of plasma membrane, they may be
involved in transmitter signals.
 many studies have been done and still going on regarding the role of microtubules
that it is associate which cancer cells.
• Drugs had been made against/ related to microtubules formation acting (drugs for
cancer cells).
– Eg: cytotoxic anti cancer drugs like vincristine & vinblastine promote disassembly of
microtubules.
– Drug paclitaxel binds with microtubules and stablizes them against depolymerizations.
Apart from that this chemotherapeutic agent prevents the formation of mitotic spindle.
– Colchicine(anti- gout) inhibits microtubule assembly.

41. • Microfilament:
– All eukaryotic cells consist microfilament.
– Long solid fibres/filaments, 4-6 nm diameter
– Comprises the contractile protein actin and are responsible for the cell motion.
– Actin in a globular form is G-actin, which is the unpolymerized actin subunits.
– Actin is the most common cell protein that account for 15% of total protein in the cell.
– Globular actin subunits polymerize to from the filamentous actin,(F-actin).
– Both polymerization and depolymerization occurs simultaneously every time where
polymerization occurs at one end depolymerization at another end of filament.
– Linked to inner face of the membrane and, through F-actin fibers attach to various
cytoskeletal structures and interact with membrane bound proteins.
– Exhibits contractile phenomena within cytoplasm, phagocytosis, secretion, transport.
– It help platelets to change and move the granule from interior of cytoplasm to
canaliculi for release chemical(release reaction of platelets).
– These structure may be involved in the generation of force for internal cell motion.
And also these filamentous actin helps in movement of chromosome & cell division.
– Motion changes the dynamic structure, membrane along with cell organelles position
through the waves of fluid in cytoplasm.
– Actin filament interacts with integrin receptors to form focal adhesion complexes
(FAC). FAC serve as a point of traction with the surface over which cell pulls itself.
– Well-developed microfilaments in muscles cells, in platelets than other cells.
• The developed contractile system in platelets consist of microtubules and
extensive network microfilaments.
• In the cells with micro villi on their epithelial surface , microfilament extend into
the microvilli.

42. Intermediate filament
• These are filamentous structure made up of various subunits.
• Average diameter of these filaments varies from 8 to 14 nm.
• Proteins of these filaments are cell specific, so used as the cellular
marker.
• For e g: cytokeratin is the marker of epithelial cells, whereas vimentin
is the marker of fibroblast
• Functions:
– connects the nuclear membrane to the cell membrane and other bio
membranes within the cell.
– Integrate the organelles within the cytoplasm of the cell.
– They provide network of additive skeletal support to the cell, as to
resist the pressure on the membrane
– in the absence of microfilaments, cell easily rupture by external
pressure.
– Blister formation in skin is common in humans when intermediate
filaments are absence or abnormal.

43. Cell adhesion molecules (desmogleins and cadherins) in desmosomes.

44. Microtubule Intermediate filament microfilament
Shape Long, non-branching Tubular hollow Double stranded helical
arrangement
diameter 25nm 10 nm 7 nm
Basic
protein
units
tubulin Various proteins Actin
Location in
cell
-mitotic spindle
- Core of cilia
-Extend across
cytoplasm connecting
desmosome and
hemidesmosome.
- The nuclear lamina
- In skin epithelium as
keratin
- Forms a network
adjacent to cell.
- Core of microvilli
- Contractile elements of
muscles.
Major
function
Provides network for
movement of
organelles.
Movement of cilia
Provide mechanical
strength and link cell
together.
Essential element of
contractile element of
muscles.

45. Motor molecular
• Helps in the movement of various cell parts, proteins and
organelles within the cell cytoplasm.
• They are 100kDa ATPases.
• Two domains: the domain attaches the cargo(cells parts to
be moved) and other domain attaches with microtubules or
actin filament
• The domain attaches with microtubules or actin is the head
part that contains ATPase for providing energy for
transportation within the cell.
• Motor molecules can be broadly divided in two categories.
– Microtubules based molecular motors
– Actin-based motor molecule

46. • Microtubule based motor molecules:
– Make movement of molecules along the microtubules, they are kinesin
& dynein
– Kinesin:
• Convention kinesin is a double headed molecule that transports its
cargo toward the negative terminal of microtubules., but sometimes
kinesin heads toward positive.
• One head attaches to microtubule and other head with the cargo.
• Involved in cell division such as mitosis and meiosis.
– Dynein:
• Double head molecules & molecules are of two types:
– Cytoplasmic dynein: function similar like convention kinesin, cargo moves
toward the negative terminal of microtubules.
– Axonemal Dynein: cilia & flagella consist dynein, thus are responsible
beating cilia and flagella.
• Actin-based motor molecules
• Movement of molecule along the actin filaments.
• These are myosin I-V ,however there are 18 types of myosin.
• Myosin-: contractile protein, contraction of intestinal villi, cell migration.

47. Junctional complexes & intercellular
junctions
• Cells are associated into tissues by various means
• Cells in tissue usually held together by extracellular matrix.
• In connective tissue such as fibroblasts, cartilage and bones,
extracellular matrix is abundant, therefore cells are sparsely
distributed.
• In muscles, muscle fibres are held together by cell-cell adhesions
• In epithelial tissue of skin, and basement membrane of tubular
structure and cavities such as alimentary tract, renal tubules, and
urinary bladder.
• These tissue has the intercellular junction where cells bound tightly
together.
• Intercellular junctions are of two types:
– Tight junctions
– Anchoring junction
• Cell to cell anchoring junction: desmosome, Zonula adherens
• Cell to basal lamina anchoring junctions: Hemidesmosome, Focal adhesion
– Gap junction

48. Tight junction
• Also called zonula occludens.
• Found in Epithelium of GI tract, nephron,
urinary tract, BBB, Blood-placental barrier,
hepato-biliary tract, choroid plexus etc
• Neighbouring cell’s membrane fused together
that obliterates the intercellular space close to
their apical margin.
• Made up of ridges, half of which is contributed
by both neighbouring cells and each half tightly
bound.
• They contains ion, water channels that make
them selectively permeable, though the
degree of leakiness varies in different
epithelia.
• Membrane proteins for making tight junction
belongs to three main families:
– Occludin
– Junctional adhesion
molecules(JAMs)
– claudins
• Many cystolic side proteins are attached to it.

49. • Serves as the selective permeability barrier, as macro
molecules pass through the epithelial cell as vesicles
(vesicular transport)
• Presence of leaky channels, where small size water
soluble molecules are permitted through tight
junction.eg: Na+ pass fairly in gut while it passage is nill in
urinary bladder.
• Osmolality gradient across the epithelium regulates the
permeability of tight junction, paracellular transport.
• In brain, this junctions between astrocytes and cerebral
endothelial cells of blood vessels provides effective BBB.
• In ciliary bodies, they form blood-aqueous barrier
between the cells of inner non-pigmented epithelium.
Functions of Tight junction

50. Gap junction
 Are also called Nexus, intercellular
space ranging from 25 to 3nm
 Made up of peculiar trans membrane
proteins known as connexons, which
further consists six identical subunits
called connexin.
 Connexin surrounds the aqueous
channel(aqua porins) of both cell
membranes become a continuous one,
that allows substances to pass directly
into one to another cell without going
ECF
 Connexons from the membrane of two
adjacent cells are lined up with one
another.
 Electrical synapses, so physiological
syncytium.
 Chemical messengers and hormones
passes through gapjunctions.
 Permit organic solutes eg: sugar, aa
with MW≤ 1000

52. Anchoring junctions
• Cell-cell anchoring junction: Desmosome & Zona
adherens.
• Desmosomes:
• the junction characterized by focal thickening of two
adjacent cell membrane, the thickened area consist dense
layer of proteins towards on the cytoplasmic side
membrane.
• Thickened both area membrane is separated by
25nm.{approx}
• Intermediary filaments are attached to the thickened areas.
• The intercellular space contains filamentous cell adhesion
materials such as desmogleins and cadherins.
• Zonula Adherens:
• Located below the tight junction.
• Major site of attachment for microfilaments
• Cadherins are present in the intercellular space at this
junction.

53. Cell to Basal Lamina Anchoring Junctions
Hemidesmosomes:
 Appearance look like a half desmosome
 Microfilaments are attached to it intracellularly.
 Contains cell adhesion material i.e Integrins
Focal Adhesions:
 Connects cell to basal lamina.
 Intra-cellularly they are associated with actin filament, therefore they assist in cell
movement.

54. System of binding of cells
• Two types:
• Extracellular binding:
– Many of CAMs bind to membrane proteins called laminins.
– Laminins are cross-shaped large membrane molecules that
have multiple receptor domains on ECF.
– CAMS bind to these extracellular receptor domains.
– Laminins are found also in skeletal muscle fibers associated
with dystrophin inside the muscle cell. Mutation on
dystrophin protein causes muscles dystrophy[genetic
inherited disease] or its absence causes destablization of
myocytes in muscular tissues or proceed to apoptosis of
myocytes.
• Intracellular binding:
– CAMs pass through the cell membrane to expose into the
interior of the cell and attach with the cytoskeleton.
– Intracellular binding of CAMs with cytoskeletal structures
enhances strength of cell adhesion.

55. Types of CAMs
• Integrin: heterodimeric proteins
• IgG super family
• Cadherins: Calcium dependent molecules that
mediates homophilic binding
• Selectins: have carbohydrates binding
domains, that resemble lectin-like structure.
• desmogleins

56. Functions of CAMs
• Zip cell to cell
• Cell movement, as it attach to cytoskeletons.
• Cellular signals
• Significant role in inflammation and wound
healing.
• Prevents apoptosis.

57. THANKYOU FOR YOUR PATIENCE