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Cell Bio Lecture 4
Cell Bio Midterm 1
| Name two functions of the plasma membrane. | Defines boundaries of the cell, maintains differences between the cytosol and extracellular environment. |
| Define receptors. | Transfer information across the membrane. |
| T or F: The plasma membrane is very rigid. | False |
| All lipids in the membrane are ______. | amphiphalic. |
| T or F: Phospholipids are the most abundant lipids in the membrane. | True |
| What are phospholipids made up of? | A polar head group and two hydrocarbon tails. |
| Most phospholipids are which type? | phosphoglycerides |
| What are the five major phospholipids in the membrane? | Phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, sphingomyelin, sphingosine |
| Which phospholipid is the only one with a negative charge? | Phosphatidylserine |
| T or F: If phosphatidylcholine is flipped on the outside of the membrane, the cell undergoes apoptosis. | False |
| What are the three types of lipids found in the membrane? | phospholipids, glycolipids, cholesterol |
| T or F: Cholesterol in the membrane decreases both permeability and fluidity. | False |
| What drives phospholipids to form a bilayer? | The hydrophobic portion of the phospholipid does not want to get in contact with water so the tails are buried and sandwiched between the head groups. |
| Forces which form bilayers provide a ______ property. | self-sealing |
| Define liposomes. | Lipid bilayers in the form of sm. spherical vesicles which can fuse with the membrane to transport molecules. |
| How is the motion of lipid molecules in the membrane measured? | Spin-labels detected by ESR and an unpaired electron. |
| What are four common movements of lipids in membranes? | flip-flop, lateral diffusion, rotation along axis, flexion |
| Define flexion. | Movement of tails around each other. |
| Flip-flop movement is catalyzed by ______ and _______. | Flippases (specific to phospholipid), scramblases (non-specific). |
| T or F: Phospholipid tails which are short and have double bonds are more fluid. | True |
| Define lipid rafts. | Different regions (domains) on the membrane with specialized function; higher concentration of proteins and glycolipids. |
| Give two examples of lipid raft areas. | viral entry, cell signaling |
| Define lipid droplets. | Storage for excess lipids, only contains hydrophobic portion. |
| What are lipid droplets used for? | Retrieved later for membrane synthesis and/or food source. |
| Which two phospholipids can be found on the outter monolayer? | Phosphatidylcholine and sphingomyelin |
| Which two phospholipids can be found on the inner monolayer? | Phosphotidylethanolamine, phosphatidylserine |
| T or F: Glycolipids are only found in the monolayer facing away from the cytosol. | True |
| _____ are the most complex type of glycolipids. | Gangliosides |
| What are some of the functions of glycolipids? | Help protect the cell; creates an electrical gradient across the membrane; cell surface recognition |
| T or F: Membrane proteins are hydrophobic only. | False |
| What is glycosylation? | Transmembrane proteins are coated with oligosaccharides on the outer side of the membrane (glycolax). |
| What are two purposes of glycolax? | Function in cell recognition, protect cells against damage. |
| What substance is used in the purification of proteins? | Detergent |
| What two types of structures are formed in protein purification with detergent? | Micelles, nanodiscs |
| Define nanodiscs. | Small patches of membrane are surrounded by a protein belt which keeps lipids soluble for transport. |
| What two movements can membrane proteins do that are similar to lipid movement? | rotation about axis, lateral movement |
| What two movements can membrane proteins not do that lipids can? | flipflop, flexion |
| _____ is used to measure lateral diffusion rates of proteins. | FRAP (fluorescence recovery after photobleaching) |
| Describe the process of FRAP. | A membrane protein is marked with a fluorescent group. The group is bleached by a laser and the time for the adjacent unbleached membrane portion to diffuse over is measured; shows if protein is mobile. |
| What is one drawback to FRAP? | FRAP cannot look at individual proteins, only an entire area. |
| Name four restriction mechanisms for membrane proteins. | tight junctions, cell-cell contact, protein anchored, formation of large aggregates |
| Name three mechanisms for membrane-bending proteins. | Hydrophobic region of protein inserts wedge between head groups, binding to lipid head groups, binding/clustering lipids with large head groups |
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goberoi
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