Bisc160 Ch 6 9 14 2015 Cell membranes are mostly lipids Lipids phospholipids Cholesterol Proteins Carbohydrates Glycoprotein modified protein Glycolipid modified lipid Membranes are made of phospholipids Long non polar tails Polar heads o o Held together by Van der Waals forces Weak Not permanent Lots of movement Phospholipids are made in the ER and then can be pushed through golgi and vesicles to the big cell membrane Covalent bonds o New membranes are made in ER then go to golgi then to vesicles to membrane Membranes are fluid o Hypothesis proteins embedded in a membrane can diffuse freely within the membrane o o Proteins are free to move around Phospholipids move around Fluidity of membranes vary Saturated vs unsaturated fatty acids Straight chains bc single bonds saturated Bent chains bc double bonds unsaturated Cholesterol Tends to stick to saturated fatty acids Increases fluidity o A lot of saturated fatty acids not a lot of movement bc packed together tightly o A lot of unsaturated very fluid bc not packed together tightly Membrane fluidity varies with temperature Internal temp determined by habitat o o Membrane lipids of cold adapted animals will have more unsaturated phospholipids Need to be able to move things across membranes easily Proteins can be embedded in membranes Peripheral membrane proteins Interact with hydrophilic heads Lack hydrophobic parts so always interacting with polar molecules Interact partly with some parts of tails and head then go into cytosol Integral membrane proteins Not fully across membrane Transmembrane protein Goes from outside to inside of cell o o o o o o o o o o o Extend fully through bilayer Has polar end hydrophobic area then polar end Carbohydrates can be embedded in membranes Cell recognition sites Cell adhesion o o o Glycolipids and glycoproteins Membranes are fluid mosaics Membranes interact with cytoskeleton inside of cell and things on the outside Membranes have several functions bc of fluid mosaic o o Compartmentalization and organization Energy transformation Energy from carbs to ATP We need to compartments in the mitochondria Cell recognition and adhesion Signaling communication o o o Membrane transport Membranes make compartments o Allows you to do chemical reactions Membranes can link cells together o o o o Cell recognition Cell adhesion Specificity Carbohydrates help with this signaling and attaching Cells are connected to each other via cell junctions Tight junctions o o Desmosomes o Gap junctions Part 2 9 16 2015 Cell membranes are connected to the extracellular matrix o o o o Integrins Bind to extracellular matrix Bind to cytoskeleton Passive Transport Membranes transport specific materials into and out of the cell Simple diffusion moving things down the concentration gradient Diffusion through channel Facilitated diffusion o Active transport Requires ATP hydrolysis Hydrolysis the addition of water to break bonds Break ATP apart to fuel a reaction Passive transport moves substances without ATP o Requires concentration gradient High concentration on one side of membrane and low on the other o May use membrane proteins o o o o o Semi permeable o o Diffusion or facilitated diffusion Molecules in solution tend to become evenly distributed o Diffusion molecules tend to become evenly distributed o o Equilibrium same number of molecules on either side of the membrane Concentration gradient Simple diffusion occurs through the lipid bilayer Small non polar hydrophobic lipids oxygen carbon dioxide Things that can diffuse across the membrane without the help of a protein Membrane proteins may aid diffusion and active transport Channel proteins ion channels Ligand or voltage gated The way that is opens Ligand something that binds to the channel that causes a reaction to make it open Molecules can just go straight through the protein Not open all the time Carrier proteins Facilitated diffusion uses membrane proteins Stimulus molecule ligand Carrier proteins Have to bind to whatever they are transporting Binding changes shape of protein so that the molecule to can through Can see specificity here Rate of diffusion is slightly different Limited by number of carrier proteins in cell membranes Diffusion can alter water in cells Isotonic same amount o Osmosis water diffusion across membrane o Hypertonic high concentrates of solutes o o Hypotonic low concentrates of solutes o Water moves out of cell when concentration of solutes in higher outside of the cell o Water moves into the cell when concentration of solutes is higher inside the cell Osmosis moves water through channels o Aquaporin protein o Regulate how much water goes in and out of cell None of passive transport uses ATP Active transport requires energy o ATP hydrolysis o Active transport is directional Phosphorylation transfer of phosphate or breaking of phosphate bond Symport move two substances in same direction sym means same o Uniport moves a single substance in one direction o o Antiport moves two different substances in opposite directions o Co transporter symports and antiports Means moving two different substances at once Often one is moving along concentration gradient and the other against Primary active transport uses ATP directly o ATP comes in and binds to membrane o Uses ATP bc moving against concentration gradient Secondary active transport depends on primary active transport o Doesn t use ATP directly Concentration gradient o o Using the previous gradient pump to move something else against its gradient Macromolecules enter and exit through the membrane Exocytosis taking out of cell Takes vesicles then unpinch the membrane to open it and then move waste out of the cell Endocytosis taking into cell Bend in membrane and take in molecule Pinch off membrane and make a vesicle out of it and move it in o o o o o o o Phagocytosis Primary way of feeding Trapping bacteria or waste products Engulfing large molecules o Pinocytosis Cell drinking o Phago and pino are forms of endocytosis Membrane receptors can control endocytosis Coated pits ex clathrin Receptor protein specificity Receptor mediated endocytosis Ex cholesterol Membrane proteins influence energy transformation Membrane proteins can transfer signals