Download Extra cellular components 15

 Extra
cellular components and connections
between the cells help coordinated cellular
activities.
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1. Cell wall of plant cells
2. Extracellular matrix of animal cells
3. Intercellular Junctions
 Cell
wall is an extracellular structure of
plant cell.
 It protects the plant cell, maintain its
shape, and prevents excessive uptake
of water. On the level of whole plant the
walls of specialized cells holds the
plant up against gravity.
 Prokaryotes, fungi and some protists
also have cell walls.
 Plant
cell walls are thick structures ranging
from 10 μm to several μm.
 The chemical composition of cell wall
varies from species to species and cell type
to cell type.
 The major constituent of cell wall is
cellulose a polysaccharide molecule. form
the microfibrils which are embedded in the
matrix of other polysaccharides pectins
and proteins.
 There
are three layers of the cell wall:
 1. Primary cell wall: It is present in young
cells, relatively thin and flexible.
 2. Middle Lamella: It is present between the
primary walls of two adjacent cells. It is a
thin layer made up of sticky material
pectins. The middle lamella glues the two
adjacent cells together.
 3. Secondary wall: When the cells matures
they secrete hardening material in the cell
wall. Some cell add this material in the
primary cell wall while others secretes an
other layer of cell wall called secondary cell
wall.
 The
cell wall is interrupted by narrow pores
carrying fine strands of cytoplasm,which
interlink the contents of adjacent.They are
called plasmodesmata. They form a
protoplasmic continuum called symplast.
 Plasmodesmata consists of a canal, lined by
plasmamembrane. It has a simple or
branched tubule known as desmotubule
which is an extension of endoplasmic
reticulum.
 Secondary
wall is deposited between the
plasma membrane and primary cell wall.
 Secondary wall has several laminated layers
which are hard and protect and support the
plant cell. Wood consists of secondary cell
wall.
 Cell wall is perforated to make channels
between the two cells. These perforations
are celled plasmodesmata. The deposition of
secondary cell wall material deposited in
such a way that it makes a structure called
pit.
Animal cell lack cell walls but they have
elaborate extra cellular matrix (ECM).
 ECM consists of glycoproteins secreted by the
cell. i.e. Collagen which form strong fiber out
side the cells. Collagen accounts half of the total
proteins in the cell.
 Collagen fibers are embedded in network of
proteoglycans, a glycoprotein of another class.
Prteoglycans consists of 95% carbohydrates and
small amount of proteins. Large proteoglycan
complex can form when hundreds of
proteoglycans become non-covalently attached
to a single long polysaccharide molecule.

ECM OF ANIMAL CELL
 Some
cells are attached to ECM by other
glycoproteins, including fibronectin.
Fibronectin and other ECM protein bind to
cell surface receptor protein called integrins.
 Integrins are built inside the plasma
membrane than span the membrane and bind
on the cytoplasmic side to associated protein
attached with the microfilaments of
cytoskeleton.
 Integrins transmit changes between the ECM
and cytoskeleton thus integrate changes
occurring outside and inside the cell.
 Fibronectin
and integrins reveals an
influential role of ECM in the lives of cells.
With the help of these ECM regulates cell’s
behavior. i.e. some cell in the developing
embryo migrates along specific path ways by
matching
the
orientation
of
their
microfilaments to the grain of the fibers in
ECM.
 ECM around a cell can influence the activity
of genes in the nucleus by mechanical
(fibrinectin, integirns and microfilaments of
cytoskeleton) and chemical (changes in
proteins thus cell functions) signalling
pathways. ECM help coordinate the behavior
of all the cells within that tissue.
Many cells of plants and animals are organized
into tissues, organs and organ systems.
Neighboring cells interacts and communicate
through special patches of direct physical
contacts.
 Plants cells have Plasmodesmata: Plant cell wall
is
perforated
with
channels
called
plasmodesmata. Cytosole passes through the
plasmodesmata and connect the chemical
environments of adjacent cells. This makes the
plant a continuum.
 Water, small solutes, proteins and RNA molecules
pass freely through plasmodesmata via channels
made by fibers of cytoskeleton.
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 Animals:
Tight Junctions, Desmosomes, and
Gap Junctions.
 These three types are common in epithelial
tissue which line the internal surface of the
body.
 Tight
Junctions:
membranes
of
the
neighbouring cells are very tightly pressed
against each other, bound together by
specific proteins. Form continuous seal
around the cell.
 They prevents the extracellular leakage
across the epithelial cells.
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Desmosomes: Anchoring junctions, function like
rivets, fastening cells together into strong
sheets. Intermediate filament of cytoskeleton
are made of keratin protein anchor desmosome
into the cytoplasm.
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Gap Junctions: Communicating junctions,
provide cytoplasmic channels from one cell to
another cell. Gap junctions consist of special
proteins that surround a pore through which
ions, sugar molecules, Aas and other small
molecules may pass. Gap junctions are important
for communication between cells in many types
of tissues, including heart muscles and animal
embryos.
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