EXTRACELLULAR COMPONENTS AND
CONNECTIONS BETWEEN CELLS
HELP COORDINATE CELLULAR
ACTIVITIES
Kate Rowe, Kylina John, Jacqueline Enriquez
Content:

Cell Walls of Plants

Intercellular Junctions of Plant Cells

ECM of Animal Cells

Intercellular Junctions of Animal Cells
How the cell wall helps coordinate
cellular activity

Protects the plant cell

Maintains its shape

Prevents excessive uptake of water
Break Down of Cell Wall
1.
Primary Cell Wall
thin and flexible
2.
Middle Lamella
sticky, thin layer of pectins
3.
Secondary Cell Wall
strong durable matrix
Cell Walls of Plants
Secondary Cell Wall
Middle Lamella
Cell Membrane
Primary Cell
Wall
Intercellular Junctions in Plants
Plasmodesmata:
channels in which plant cell walls are perforated with.
Functions of plasmodesmata include:
-Allowing cytosol to pass through, which connects
cells to unify plant into one living thing.
-Water and small solutes pass from cell to cell.
-Macromolecules pass through and are transported
on cytoskeleton.
Plasmodesmata in Plant Cells
What is the extracellular matrix
(ECM)?



Something that is made by virtually all multi-cellular
organisms.
Elaborate covering outside animal cell membranes,
occupying the space between cells. It is composed of:
◦ Collagen, proteoglycans, and fibronectin, which the
cell secretes.
◦ Different from the plant extracellular matrix, which is
composed of cellulose.
Many ECM components are involved in cell-to-cell
interactions.
Components of the ECM

Collagen
◦ Most abundant glycoprotein (about half of the total protein in
the body).
◦ Forms strong fibers outside of the cell.
 Fibers are embedded in a network made of proteoglycans.

Proteoglycans
◦ Collagen fibers are embedded in a network made from
proteoglycans.
◦ Are another class of glycoproteins that consists of a small core
protein with many carbohydrate chains covalently attached.
◦ Large complexes can form when hundreds of proteoglycans
become non-covalently attached to a single long polysaccharide
molecule.
Components (cont.)

Fibronectin
◦ Glycoprotein that attaches the ECM to the cell itself.
◦ Binds to cell surface receptors called integrins, which
are built into the plasma membrane of the cell.

Integrins
◦ Cell surface receptor that connects to fibronectin,
which attaches to the ECM
◦ Span the membrane and bind on their cytoplasmic
side to associated proteins attached to microfilaments
of the cytoskeleton.
◦ Transmit’s changes between the ECM and the
cytoskeleton – it integrates changes occurring outside
and inside the cell.
Collagen
Proteoglycan
complex
EXTRACELLULAR
FLUID
Polysaccharide
molecule
Carbohydrates
Fibronectin
Core
protei
n
Integrins
Proteoglycan
molecule
Plasma
membran
e
Proteoglycan complex
Microfilaments
CYTOPLAS
M
Fig. 6-30
ECM Effect on Behavior


By communicating with a cell through integrins, the
ECM can regulate a cell’s behavior.
ECM can influence the activity of genes in the nucleus.
◦ Speculated that information probably reaches the nucleus by a
combination of chemical and mechanical signaling pathways.
 Mechanical includes fibronectin, integrins, and microfilaments of the
cytoskeleton.
 The cytoskeleton may then trigger chemical signaling pathways inside
the cell, leading to changes in the proteins being made by the cell and
therefore in its function.

The ECM may help coordinate the behavior of all the
cells within that tissue.
◦ Direct connections (intercellular junctions) between cells also
function in this coordination.
Intercellular Junctions in Animal Cells

Tight Junctions: Specific proteins bind cell
membranes which are pressed against
each other.
◦ Function: Tight Junctions prevent extracellular
fluid from leaking across epithelial cells.
Intercellular Junctions in Animal Cells

Desmonsomes: also known as “anchoring
junctions,” desmonsomes are like rivets
that fasten cells together.
◦ Desmonsomes are anchored to the cytoplasm
by filaments made of keratin proteins.
Intercellular Junctions in Animal Cells

Gap Junctions: also known as
“communicating junctions,” gap junctions
act as cytoplasmic channels between cells.
◦ Function: Each pore is surrounded by
membrane proteins which allow ions, sugars,
amino acids, and other things cells need to
pass from cell to cell.
Intercellular Junctions in Animal Cells