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 PlantsSecondary Cell Wall Cell

Membrane

Primary Cell WallMiddle Lamella

Intercellular Junctions in PlantsPlasmodesmata: 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 ECMCollagen

◦ 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.

Fig. 6-30

EXTRACELLULAR FLUID

Collagen

Fibronectin

Plasmamembrane

Micro-filaments

CYTOPLASM

Integrins

Proteoglycancomplex

Polysaccharidemolecule

Carbo-hydrates

Coreprotein

Proteoglycanmolecule

Proteoglycan complex

ECM Effect on BehaviorBy 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