BIOL 1411 1st Edition Lecture 7Outline of Last Lecture 1. Finish up last lecture on organelles2. Function of cellular membranes3. Membrane structureOutline of Current Lecture 1. More cell membrane functions and details2. Transporting substances through membrane3. DiffusionCurrent Lecture- Tight junctions: prevent leaking between cells- Desmosomes: act as spot welds- Gap junctions: allow communication- Cells also attach to an extracellular matrixo Extracellular structures are secreted outside of plasma membraneo In eukaryotes, extracellular structures have a prominent fibrous macromolecules in a gel-like mediumo 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 matrixo Integrin Links ECM and cytoskeleton Transmembrane protein that binds to the matrix outside epithelial cells, and to actin filaments inside the cellsThese 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 membraneo Selective permeabilityo Passive transport Movement by diffusion, no outside energy required Concentration gradient is the driving force- Simple diffusiono Directly across the phospholipid bilayer- Facilitated diffusiono 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 allowion passage, gate opens when protein is stimulated to change shape. Aquaporins (forwater)o Active transport Movement against concentration gradient Via protein pump that required ATP energy - Diffusion rateo Complex solutions, the diffusion varies between all individual soluteso Physical factors  Diameter of the molecules or ions Electrical charge Temp of the solution Concentration gradiento 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