biological membranes

Question 1

hydrophobic effect

Answer 1

stabilizes structures (lipid bilayers & vesicles) in which lipids with some polar and some nonpolar regions can protect their nonpolar regions from interaction with the very polar solvent, water

Question 2

biological membranes functions

Answer 2

define external boundaries, control molecular traffic, divide cells-organelles, organize reaction sequences, cell-to-cell communication, transporters, receptors, adhesion molecules, within the cell-energy transduction

Question 3

glycerophospholipids, sphingolipids, and sterols are virtually insoluble in water ->

Answer 3

spontaneously form microscopic lipid aggregates when mixed with water

Question 4

micelles

Answer 4

spherical structures containing amphipathic molecules

Question 5

bilayer

Answer 5

lipid aggregate in which two lipid monolayers (leaflets) form a two-dimensional sheet

Question 6

vesicle (liposome)

Answer 6

forms spontaneously when a bilayer sheet folds back on itself to form a hollow sphere

Question 7

the _________________ of each membrane type is reflected in its unique lipid composition

Answer 7

functional specialization

Question 8

single membrane surrounds…

Answer 8

endoplasmic reticulum, golgi apparatus, lysosomes, various small vesicles

Question 9

double membrane surrounds…

Answer 9

nucleus, mitochondrion, chloroplasts

Question 10

fluid mosaic

Answer 10

pattern formed by individual lipid and protein units in a membrane -> pattern can change while maintaining the permeability of the membrane

Question 11

transporters

Answer 11

move specific organic solutes and inorganic ions across the membrane

Question 12

receptors

Answer 12

sense extracellular signals and trigger molecular changes in the cell

Question 13

ion channels

Answer 13

mediate electrical signaling between cells

Question 14

adhesion molecules

Answer 14

hold neighboring cells together

Question 15

peripheral membrane proteins

Answer 15

associate with the membrane through electrostatic interactions and hydrogen bond -> released by mild detergents or by interfering with charge/hydrogen bonding

Question 16

integral membrane proteins

Answer 16

firmly embedded within the lipid bilayer; monotopic, polytopic, removable only by hydrophobic agent

Question 17

amphitropic proteins

Answer 17

associate reversibly with membranes- found in both membranes and the cytosol

Question 18

monotopic proteins

Answer 18

have small hydrophobic domains that interact with only a single leaflet of the membrane

Question 19

bitopic proteins

Answer 19

span the bilayer once, extending on either surface- have a single hydrophobic sequence somewhere in the molecule

Question 20

polytopic proteins

Answer 20

cross the membrane several times- have multiple hydrophobic sequences of ~20 residues that each cross the membrane when in the a-helical conformation

Question 21

type 1 integral membrane protein

Answer 21

glycophorin

Question 22

type III integral membrane protein

Answer 22

bacteriorhodopsin

Question 23

hydropathy index

Answer 23

expresses the free-energy change associated with the movement of an amino acid side chain from a hydrophobic environment to water- ranges from highly exergonic to highly endergonic

Question 24

deltaG<0

Answer 24

hydrophilic

Question 25

deltaG>0

Answer 25

hydrophobic

Question 26

hydropathy plot

Answer 26

average hydropathy index plotted against residue number
window: segment of given length
hydropathy index (y-axis): average hydropathy for a window
residue number (x-axis): residue in the middle of the window

Question 27

B-barrel

Answer 27

structural motif in which 20+ transmembrane segments form B sheets that line a cylinder- stabilized by intrachain hydrogen bonds

Question 28

porins

Answer 28

proteins that allow certain polar solutes to cross the outer membrane of gram-negative bacteria

Question 29

what side chains serve as membrane interface anchors?

Answer 29

tyr & trp

Question 30

positive-inside rule

Answer 30

positively charged Lys & Arg residues in the extramembrane loop of membrane proteins occur more commonly on the cytoplasmic face

Question 31

membrane trafficking

Answer 31

process by which membrane lipids and proteins that are synthesized in the ER move to their destination organelles or to the plasma membrane

Question 32

lipids and proteins undergo____________ in the _____. this dictates the eventual location of the mature protein.

Answer 32

covalent modifications; golgi

Question 33

glycosylation

Answer 33

attachment of oligosaccharides to proteins- typically on the outer face of the plasma membrane; attachment of 1+ lipids: serve as hydrophobic anchors or targeting tags

Question 34

GPI-anchored protein

Answer 34

exclusively on the outer face and are clustered in certain regions