BIOL 1411 1st Edition Lecture 7 Outline of Last Lecture 1 Finish up last lecture on organelles 2 Function of cellular membranes 3 Membrane structure Outline of Current Lecture 1 More cell membrane functions and details 2 Transporting substances through membrane 3 Diffusion Current Lecture Tight junctions prevent leaking between cells Desmosomes act as spot welds Gap junctions allow communication Cells also attach to an extracellular matrix o Extracellular structures are secreted outside of plasma membrane o In eukaryotes extracellular structures have a prominent fibrous macromolecules in a gel like medium o Functions Holds cell together in tissues Contributes to properties of bone cartilage skin etc Acts as a filter of materials passing through different tissues Orients cell movements in development and tissue repair Plays a role in chemical signaling o Cell membranes can adhere to extracellular matrix o Integrin Links ECM and cytoskeleton Transmembrane protein that binds to the matrix outside epithelial cells and to actin filaments inside the cells These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Binding is noncovalent and reversible to facilitate cell movement Membranes are constantly forming transforming fusing and breaking down Substances transporting across a cell membrane o Selective permeability o Passive transport Movement by diffusion no outside energy required Concentration gradient is the driving force Simple diffusion o Directly across the phospholipid bilayer Facilitated diffusion o Across a membrane via channel or carrier proteins Carrier protein Membrane proteins that act as channels binds to transported solutes to speed rate through bilayer Example sugar transporters Note Polar and charged solutes cannot diffuse directly across membrane Channel proteins Integral membrane proteins that form a central pore lined with polar amino acids Solute streams down the gradient Examples gated ion channels open to allow ion passage gate opens when protein is stimulated to change shape Aquaporins for water o Active transport Movement against concentration gradient Via protein pump that required ATP energy Diffusion rate o Complex solutions the diffusion varies between all individual solutes o Physical factors Diameter of the molecules or ions Electrical charge Temp of the solution Concentration gradient o Without barriers only these factors will affect diffusion o Rate is rapid across short distances diameter of cell o Diffusion across a membrane Permeability of phospholipid bilayer affects rate Steroid molecules rapid rate Small protein slow rate