biological membranes Flashcards

1
Q

hydrophobic effect

A

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

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2
Q

biological membranes functions

A

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

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3
Q

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

A

spontaneously form microscopic lipid aggregates when mixed with water

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4
Q

micelles

A

spherical structures containing amphipathic molecules

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5
Q

bilayer

A

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

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6
Q

vesicle (liposome)

A

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

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7
Q

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

A

functional specialization

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8
Q

single membrane surrounds…

A

endoplasmic reticulum, golgi apparatus, lysosomes, various small vesicles

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9
Q

double membrane surrounds…

A

nucleus, mitochondrion, chloroplasts

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10
Q

fluid mosaic

A

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

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11
Q

transporters

A

move specific organic solutes and inorganic ions across the membrane

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12
Q

receptors

A

sense extracellular signals and trigger molecular changes in the cell

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13
Q

ion channels

A

mediate electrical signaling between cells

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14
Q

adhesion molecules

A

hold neighboring cells together

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15
Q

peripheral membrane proteins

A

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

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16
Q

integral membrane proteins

A

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

17
Q

amphitropic proteins

A

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

18
Q

monotopic proteins

A

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

19
Q

bitopic proteins

A

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

20
Q

polytopic proteins

A

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

21
Q

type 1 integral membrane protein

A

glycophorin

22
Q

type III integral membrane protein

A

bacteriorhodopsin

23
Q

hydropathy index

A

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

24
Q

deltaG<0

A

hydrophilic

25
deltaG>0
hydrophobic
26
hydropathy plot
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
27
B-barrel
structural motif in which 20+ transmembrane segments form B sheets that line a cylinder- stabilized by intrachain hydrogen bonds
28
porins
proteins that allow certain polar solutes to cross the outer membrane of gram-negative bacteria
29
what side chains serve as membrane interface anchors?
tyr & trp
30
positive-inside rule
positively charged Lys & Arg residues in the extramembrane loop of membrane proteins occur more commonly on the cytoplasmic face
31
membrane trafficking
process by which membrane lipids and proteins that are synthesized in the ER move to their destination organelles or to the plasma membrane
32
lipids and proteins undergo____________ in the _____. this dictates the eventual location of the mature protein.
covalent modifications; golgi
33
glycosylation
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
34
GPI-anchored protein
exclusively on the outer face and are clustered in certain regions