E XTRACELLULAR C OMPONENTS AND C ONNECTIONS B ETWEEN C ELLS H ELP C OORDINATE C ELLULAR A CTIVITIES 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 Cell Membrane Primary Cell Wall Middle Lamella

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.

Fig EXTRACELLULAR FLUID Collagen Fibronectin Plasma membran e Micro- filaments CYTOPLAS M Integrins Proteoglycan complex Polysaccharide molecule Carbo- hydrates Core protei n Proteoglycan molecule Proteoglycan complex

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