Lecture 15.3

• Cells that are close and fr apart must communicate to survive.
• Extracellular matrix (ECM) is a wall that forms just beyond the plasma membrane.
• The ECM helps define cell shape, attaches cells to eachother, and acts as a first defence.
• the cell wall in plants prevents cells from lysing (bursting).
• There are three types of cell junctions in Animals: Tight, Adhesion, and Gap junctions.
• In tight junctions the membrane proteins of two ajacent cells stich together. (can loosen)
• In adhesion junctions, desmosomes form secure adhesions like tacs.
• In gap junctions adjacent cells are connected with channels to allow small molecules to flow through.
• The plant cell walls prevent direct interactions between cells.
• Plant cells are connected by gabs in their cell walls called plasmodesmata.
• Plant cells can transport molecules through two pathways: symplast - pathway through shared cytoplasm

  Apaplast - pathway through extracellular space (i.e. cell wall)
• Cells use signaling molecules such as neurotransmitters and hormones to communicate.
• Both neurotransmitters and hormones must bind to the receptors on the target cell.
• Only cells with an appropriate signal receptor will respond to a particular signaling molecule.
• Lipid soluble signaling molecules diffuse across plasma membranes.
• Lipid insoluble signaling molecules do not diffuse across plasma membranes.
• Signal receptors are dynamic (number may change).
• Signal receptors can be blocked (beta blockers)