BIOL 213 1st EditionExam # 2 StudyGuideLecture 7 (September 25)Describe the cell membraneIt is a selectively permeable lipid bilayer that regulates what goes into and comes out of the cell.What is its composition?It’s composed of lipids and proteins. There’s usually an equal amount of each.There are three main kinds of lipids: phospholipids (most abundant), glycolipids and sterols. There are two main kinds of proteins: integral and peripheralDescribe the three types of lipid motions in a membraneLateral diffusion – lipids move side to side within the same leaflet. Most common.Flexion – the fatty acid chains move apart from each other like scissors because of thermal energyRotation – when lipids spinWhat is the movement that rarely happens? Why?Flip-flopping – when lipids switch sides of the membrane. This doesn’thappen because the hydrophilic head of the lipid would have to cross the extremely hydrophobic interior of the membraneDescribe the process by which lipids get to the correct side of the membraneLipids are always synthesized in and added to the cytosolic side of the ER membrane, and the enzyme flipase flips lipids to the correct side of the membrane.Do all lipid types have a unique flipase? Why or why not?No. Only lipids that have to be flipped to the other side of the membrane have a corresponding flipase.Describe the path of a lipid from synthesis to the transportation to other membranes.The lipid is synthesized in the ER membrane added to the cytosolic side. If a lipid needs to be on the side of the membrane that does not face the cytosol, flipase flips the lipid to the other side of the membrane. Lipids are always flipped in the ER membrane. A vesicle pinches off of the ER membrane with the cytosolic side still facing the cytosol. The vesicle them fuses with the target membrane. The leaflet on the outside of the vesicle that was exposed to the cytosol still facesthe cytosol after it fuses with the membrane.What are the two main classifications of membrane proteins? Describe each.Integral proteins – these proteins are attached directly to the membrane. Peripheral proteins – these proteins are attached to integral proteins via noncovalent bonds.What are the three different kinds of integral proteins?Transmembrane – these proteins go all the way through the membrane.Membrane-associated – only parts of these proteins are inserted in the membrane; they don’t go all the way through.Lipid-linked – these proteins are covalently bonded to a lipid of the membrane, but aren’t inserted in the membrane.Neither lipid-linked nor peripheral proteins are inserted in the membrane. Why is a lipid-linked protein not considered peripheral?Lipid-linked proteins are attached to a lipid by a covalent bond. Peripheral proteins are attached to proteins by noncovalent bonds. Attaching one protein to another protein by a covalent bond just makes one big protein.How does the amino acid composition of a protein determine whether or not it’s an integral protein?The parts of integral proteins that are inserted in the membrane haveamino acids that have nonpolar, hydrophobic side chains. The partsof the protein that aren’t inserted in the membrane have amino acidswith hydrophilic side chains.How are α helices of a transmembrane protein involved with transportation of molecules?α helices can insert themselves into the membrane if they have nonpolar, hydrophobic side chains. When multiple amphipathic α helices group together, they can create an aqueous pore through which larger and polar molecules can diffuse.How are β sheets of a transmembrane protein involved with transportation of molecules?A large curved β sheet can be inserted in the membrane in a way similar to the α helices so that an aqueous pore is created. This is called a β barrel.Why can’t a single strand of β sheet cross the membrane?The edges of a β sheet expose the hydrogen bonds that link the amino acids together to form the β sheet. These are hydrophilic and can therefore not be exposed to the hydrophobic interior of the cell membrane.(Refers to different lectures)What kind of transport protein would the aqueous pores of α helices and β sheet be considered? What kind of transport are they involved in?Channel proteins. They are involved in passive transport, meaning no energy input is required to move molecules, they move down their gradients. Passive transport is also known as facilitated diffusionWhat kind of molecules can be transported via facilitated diffusion?Large uncharged polar molecules and ions.What is the other kind of transport? Describe it.Active transport. This requires an energy input of some kind to move amolecule in a direction that it wouldn’t naturally go (ΔG > 0).What is the kind of transport protein that can be involved in active transport?Carrier proteins. Are they only involved in active transport? Explain.No. Uniporters utilize passive transport.What are the three kinds of carrier proteins? Describe each.Uniporters – allow passive diffusion. They let molecules move down their gradients. They transport one molecule at a time.Symporters – these couple the energy of one molecule moving down its gradient with a molecule that needs to be moved against its gradient. Both molecules move in the same direction.Antiporters – these also couple the energy of one molecule moving down its gradient with a molecule that needs to be moved against its gradient. The molecules move in opposite directions.Are membrane proteins mobile? What experiment proved this?Yes. The experiment that fused the mouse and human cell proved this because the membrane proteins spread evenly across the new, larger cell.Are all membrane proteins freely diffusible? Explain.No. Some are restricted to specific membrane domains.How are membrane proteins restricted to domains?They can be tethered to the cell cortex. This is a network of proteins on the inner layer of the plasma membrane.They can be tethered to the extracellular matrix. This is a network of proteins and carbohydrates on the outside of cell.They can be involved in cell-cell adhesion. This holds them firmly in place because they are involved in holding two cells together.They can be limited by tight junctions. Tight junctions are also membrane proteins. These are anchored to a specific location. They limit the domains of other proteins by not allowing other proteins past them.What is a detergent? How is it similar to lipids? How is it