BIOL 218 1st EditionExam # 3 Study GuideChapter 11Lipid bilayer: made of 2 sets of phospholipids - Asymmetrical- 2 halves have different sets of phospholipids and glycolipids - Made in ER and can be exported to other membranes by budding and fusion of vesiclePhospholipid: looks like head and legs- amphipathic- Has hydrophilic heads and hydrophobic tails - Tails can have single bonds (saturated) or double bonds (unsaturated)Phospholipid movement within membrane- Lateral diffusion-switches places with neighbor- Flexion-moves side to side, dances- Flip flop-bottom monolayer phospholipid switches with phospholipid in top monolayer using ATP- Rotation-turns aroundGlycolipids: provides energy & acts as cell surface markerCell cortex: meshwork of fibrous proteins that are attached to cytosolic face of membrane- Support & strengthens cell membrane - Attached to membrane via transmembrane proteinsFlippasses: catalyzes transfer of phospholipid molecules to opposite monolayer- Process: phospholipids are added to cytosolic half of bilayer then scramblases transfer random phospholipids from one monolayer to another - Orientation is preservedMembrane involvement:  Receives info through receptors Imports or exports molecules through channels and/or pumps Allows movement or expansion through cytoskeleton and by adding new membrane Encloses cellMembrane proteins: - Formed by helices or beta-sheets but alpha helices are most common- Aqueous version allow water soluble molecules to pass into cell- Never stay totally open - When formed by alpha helices, they can open and close- Occupies 50% of plasma membrane- Carries out most membrane functions through transporters, anchors, receptors and enzymes- Types: o Peripheral: transmembrane, monolayer associated alpha helix, and lipid linkedo Peripheral: protein attachedLipid linked: integral membrane protein assocating with lipid bilayer- Lies entirely on outside of bilayer- Can be on cytosolic or extracellular side- Has 1 or more covalently bound lipid groupsProtein-attached: peripheral membrane protein that associated with lipid bilayer- Is bound indirectly with other membrane proteins- Can be on cytosolic or extracellular sidePhosphoaditylcholine: most common type of chemical - Mainly structural and found on outside Phosphoatidylserine: - Found inside cell- Flips to outside during apoptosisPhosphoatidylethanolamine:- Found on inside - Involved in membrane fusionInositolphospholipids: - Used to import signaling moleculesTransmembrane proteins: extend through bilayer- Amphipathic- Made by alpha helix of beta-barrel- Act as receptors to relay signal from extracellular environment to other systems- Have peptide bonds on hydrophilic heads- Hydrophilic parts of backbone form hydrogen bonds with one another- Example: cannabinoidBeta-barrel: beta sheet curved into cylinder- Contains amino acids that face inside of barrel- Is an example of transmembrane protein- Are amphipathic- Are less versatile than alpha helix because there is a limit to how tightly it can be curved which means it only forms wide channels Red Blood Cells (RBSs):- Provides support for plasma membrane - Maintains cell shape- Has simple cortex that has been the most researched one- Main component of its’ cortex is spectrin(ropelike structure)o Mutations in spectrin can lead to anemia Spectrin: ropelike structures- Linked to specific transmembrane proteins by intracellular attachments- If it has genetic abnormalities it can lead to anemia which causes fewer RBCs that in correctly shaped and fragileCholesterol: - Amphipathic- Maintains fluidity and structure of membrane- Makes up about 20% of lipidsMembrane domains: functionally specialized regions on all cell or otherwise organelle surface- Helps organize plasma membrane - Stops cell proteins from floating freely in membrane- Leads to formation of lipid raftsLipid rafts: specialized membrane micro domains that compartmentalize cellular processes- function as organizing centers for making of signaling molecules- affect membrane fluidity and receptor trafficking- very ordered and tightly packed but can float freely in lipid bilayer- most commonly found in plasma membrane but also in Golgi body and lysosomesSphingomyelin: myelin sheathing - Mostly outside and play role in signalingLiposomes:- Pure phospholipids added to water- Creates artificial bilayerTight junctions: act as seal- Form barriers allowing for asymmetric distribution of membrane proteins - Restricts proteins movement- Example: blood brain barrier & gut lining Carbohydrate layer: sugar coating- Located on noncystolic side- Outside of lipid bilayer- Protects cell surface form mechanical and chemical damage- Majority of proteins in plasma membrane have oligosaccharides (short chains of sugars) linked to them - Proteoglycans: 1+ long chain polysaccharide chain attached to membrane protein- Absorbs water which aides in mobility and stops it from sticking - Helps with cell to cell recognition and adhesionQuestions:How are protein movements restricted?1. Tether to cell cortex inside cell 2. Have extracellular matrix molecules outside cell3. Tether to protein from another cell 4. Have diffusion barriers which restrict proteins to specific domains using tight junctions What determines how polypeptide chains cross lipid bilayer as alpha helices? Hydrophobicity Alpha helix forms into basketsWhy does the phospholipid bilayer spontaneously close? Because it’s energetically favorable Lowers delta G of environment Protects hydrophobic tails  It’s fundamental to creation and the living cellWhat destroys the lipid bilayer and releases membrane proteins? Detergento Has hydrophilic tails (cone like) o When in water aggregates to from micelleso Used to break open membranes when making cell lysate for SDS-PAGEo Disrupts hydrophobic interactions by binding to them with their hydrophobic tailsWhat effect does cholesterol have? Stiffens membrane by filling in space between neighboring phospholipid molecules left by kinks Makes membrane more rigid and less permeable Maintains fluidity Chapter 12Membrane transport proteins: transfers small water soluble molecules around membrane- Selective because each type of protein transfers particular molecule (point of regulation)- Have 2 types:1. Transporters2. ChannelsChannels: “gateway”- Are tiny hydrophilic pores which allow ions to pass by diffusion- Discriminate on size and electrical charge- Very selective-