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Biochemistry > 11.1 The Composition and Architecture of Membranes > Flashcards

11.1 The Composition and Architecture of Membranes Flashcards

1
Q

the lipid bilayer is

A

stable in water

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2
Q

glycerophospholipids, sphingolipids, and sterols:

A

-virtually insoluble in water
-spontaneously form microscopic lipid aggregates when mixed with water

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3
Q

hydrophobic interactions

A

the clustering of hydrophobic molecule surfaces in an aqueous environment to find the lowest-energy environment by reducing the hydrophobic surface area exposed to water

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4
Q

micelles

A

spherical structures containing amphipathic molecules arranged with hydrophobic regions in the interior and hydrophilic head groups on the exterior

favored when the cross-sectional area of the head group is greater than that of the acyl side chain(s)

wedge-shaped

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5
Q

bilayer

A

lipid aggregate in which two lipid monolayers (leaflets) form a 2-dimensional sheet

favored when the cross-sectional areas of the head group and acyl side chain(s) are similar

cylindrical

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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

fluid mosaic

A

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

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8
Q

functions of biological membranes

A

flexible
self-repair
selectively permeable

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9
Q

flexible

A

permit shape changes that accompany cell growth and movement

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10
Q

self-repair

A

permit exocytosis, endocytosis, and cell division

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11
Q

selectively permeable

A

serve as molecular gatekeepers

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12
Q

proteins and enzymes in and on membranes

A

transporters
receptors
ion channels
adhesion molecules

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13
Q

transporters

A

move specific organic solutes and inorganic ions across the membrane

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14
Q

receptors

A

sense extracellular signals and trigger molecular changes in the cell

-movement of a signal, not a molecule!

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15
Q

ion channels

A

mediate electrical signaling between cells

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16
Q

adhesion molecules

A

hold neighboring cells together

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17
Q

endomembrane system is dynamic and functionally differentiated

A

single membrane
double membrane

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18
Q

single membrane surrounds

A

endoplasmic reticulum (make protein)
golgi apparatus (post translational modification sorting of that protein)
lysosomes
various small vesicles

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19
Q

double membrane surrounds

A

nucleus
mitochondrion
chloroplasts (in plants)

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20
Q

general sequence of membrane trafficking for an extracellular protein

A

endoplasmic reticulum
cis Golgi
trans Golgi
secretory vesicle
secretion from the cell

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21
Q

the functional specialization of each membrane type is reflected in

A

its unique lipid composition

22
Q

membrane trafficking

A

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

23
Q

where do lipids and proteins undergo covalent modifications?

A

in the Golgi apparatus- dictates the eventual location of the mature protein

24
Q

changes in lipid composition during membrane trafficking

A

sphingolipids and cholesterol largely replace phosphatidylcholine

25
Q

how are plasma membrane lipids distributed

A

plasma membrane lipids are asymmetrically distributed between the two leaflets of the bilayer

26
Q

lipid transfer proteins (LTPs)

A

soluble proteins that contain a hydrophobic lipid-binding pocket to carry a lipid from one membrane to another

can be bispecific

move lipids basically
sometimes ATP dependent

27
Q

groups of membrane proteins

A

-receptors for extracellular signals
-transporters to carry specific polar or charged compounds across the plasma membrane or between organelles
-enzymes

28
Q

posttranslational modification of membrane proteins

A

glycosylation
attachment of 1+ lipids

29
Q

glycosylation

A

attachment of oligosaccharides to proteins
-typically on the outer face of the plasma membrane

30
Q

attachment of 1+ lipids

A

serve as hydrophobic anchors or targeting tags

31
Q

membrane proteins differ in the nature of their association with the membrane bilayer

A

integral membrane proteins
peripheral membrane proteins
amphitropic proteins

32
Q

integral membrane proteins

A

firmly embedded within the lipid bilayer

33
Q

peripheral membrane proteins

A

associate with the membrane through electrostatic interactions and hydrogen bonding with hydrophilic domains of integral proteins and charged head groups of membrane lipids

more loose

34
Q

amphitropic proteins

A

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

35
Q

monotopic proteins

A

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

36
Q

bitopic proteins

A

span the bilayer once, extending on either surface

-have a single hydrophobic sequence somewhere in the molecule

37
Q

polytopic

A

cross the membrane several times

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

38
Q

phospholipids lie

A

-on the protein surface
-at interfaces between monomers of multisubunit proteins, forming a “grease seal”

39
Q

the topology of an integral membrane protein can often be predicted

A

from it sequence

40
Q

integral membrane protein: an alpha-helical sequence of

A

20-25 residues (each 1.5A) is just long enough to span the thickness (30A) of the lipid bilayer

stabilized by intrachain hydrogen bonding and the hydrophobic effect

41
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

42
Q

hydropathy plots

A

average hydropathy index plotted against residue number

easy way for questions to be asked about membrane proteins

43
Q

window

A

segment of given length

44
Q

hydropathy index (y-axis)

A

average hydropathy for a window

45
Q

residue number (x-axis)

A

the residue in the middle of the window

46
Q

beta barrel

A

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

can’t assume all beta barrels are porins

47
Q

porins

A

proteins that allow certain polar solutes to cross the outer membrane of gram-negative bacteria
-have beta barrels lining the transmembrane passage

48
Q

in beta conformation:

A

-7 to 9 residues are needed to span a membrane
-alternating side chains project above and below the sheet

*alternating: hydropathy index does not work very well

49
Q

in beta strands of membrane proteins:

A

-every second residue in the membrane-spanning segment is hydrophobic and interacts with the lipid bilayer
-aromatic side chains are commonly found at the lipid-protein interface

50
Q

which amino acid side chains serve as membrane interface anchors

A

Tyr and Trp

51
Q

positive-inside rule

A

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

52
Q

GPI-anchored protein

A

exclusively on the outer face and are clustered in certain regions

extracellular spot of PM

Biochemistry (8 decks)

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