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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
Created by: goberoi
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