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BS202 > 15.1 The Structure of the Plasma Membrane > Flashcards

15.1 The Structure of the Plasma Membrane Flashcards

1
Q

what are the main functions of a cell’s plasma membrane?

A
  1. defining the cell boundary → separates it from the environment
  2. serves as a selective barrier → determines the composition of the cytoplasm; allows only certain molecules through to the cytoplasm
  3. mediating the interactions between the cell and its environment (mostly through embedded proteins)
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2
Q

the fundamental structure of the plasma membrane

A

phospholipid bilayer

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3
Q

describe the electron micrograph of the phospholipid bilayer in the plasma membrane

A
  • darkly stained electron-dense polar head groups
  • bands of lightly stained hydrophobic fatty acids alternate with polar head groups
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4
Q

proteins embedded in the bilayer carry out functions including (1) and (2)

A
  1. selective transport
  2. cell-cell recognition
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5
Q

what are the 5 major phospholipids that make up the animal plasma membrane

A

Outer leaflet
1. phosphatidylcholine
2. sphingomyelin

Inner leaflet
3. phosphatidylethanolamine
4. phosphatidylserine
5. phosphatidylinositol

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6
Q

which PM phospholipids have an overall negative charge? neutra/no charge?

A

Negative: phosphatidylserine, phosphatidylinositol
Neutral: phosphatidylcholine, sphingomyelin, phosphatidylethanolamine

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7
Q

the overall negative charge of the inner leaflet of the plasma membrane is largely due to the predominance of ()

A

phosphatidylserine

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8
Q

() is the only major PM phospholipid that is synthesized in the Golgi

A

sphingomyelin

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9
Q

localization of phosphatidylserine in the inner leaflet plays an important role in ()

A

programmed cell death

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10
Q

In addition to the phospholipids, animal cell plasma membranes also contain:

A
  1. glycolipids (minor component)
  2. cholesterol (major component)
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11
Q

glycolipids are found exclusively on the () of the PM

A

outer leaflet

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12
Q

cholesterol exists as a major component of the PM having a () molar amount ratio as phospholipids

A

1:1

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13
Q

cholesterol is more concentrated on the (1) leaflet of the PM due to high affinity for (2)

A
  1. outer
  2. sphingomyelin
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14
Q

The two general features of lipid bilayers are:

A
  1. water-insoluble hydrophobic fatty acid chains → bilayer serves as a barrier between 2 aqueous environments by being impermeable to water-soluble molecules (ions and most biological molecules)
  2. viscosity (as a fluid) → lateral diffusion of lipids and proteins is possible because the membrane is soft and flexible
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15
Q

states that membranes are 2D fluids with proteins inserted into bilayers; proteins and lipids are able to diffuse laterally through the membrane

A

fluid mosaic model

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16
Q

the fluid mosaic model was proposed by () in 1972

A

Sanger and Nicolson

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17
Q

how was lateral movement of embedded proteins in the PM first shown?

A
  • fusion of human and mouse cells to produce human-mouse cell hybrids
  • antibodies of each cell were labeled with different fluorescent dyes to easily distinguish them
  • after incubation, the differently labeled antibodies were shown to have mixed and were no longer separated from each other
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18
Q

what are the 2 classes of membrane-associated proteins (MAPs)?

A
  1. peripheral membrane proteins
  2. integral membrane proteins
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19
Q

() are MAPs that are indirectly associated to the plasma membrane through protein-protein interactions

A

peripheral membrane proteins

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20
Q

the bonds associating peripheral membrane proteins are usually ()

A

ionic

21
Q

bonds associating the peripheral MAPs are easily disrupted by (1), allowing the proteins to be soluble in (2)

A
  1. polar reagents
  2. aqueous environments
22
Q

examples of peripheral MAPs

A

proteins of the cortical cytoskeleton (spectrin, actin, band 4.1)

23
Q

MAPs with hydrophobic portions that are directly inserted into the lipid bilayer

A

integral membrane proteins

24
Q

integral MAPs can be dissociated from the PM only by reagents that disrupt ()

A

hydrophobic interactions

25
Q

what characteristic of detergents allow them to disrupt the association of integral MAPs from the PM?

A

detergents have hydrophobic and hydrophilic portions → amphiphatic molecules that can solubilize integral proteins

26
Q

integral membrane proteins are either:

A
  1. transmembrane proteins
  2. anchored to the plasma membrane by covalently attached lipids
27
Q

these integral MAPs span the lipid bilayer with portions exposed on both sides of the membrane

A

transmembrane proteins

28
Q

most transmembrane proteins of PM are (1) with their (2) exposed on the surface of the cell

A
  1. glycoproteins
  2. oligosaccharides
29
Q

give 2 major examples of transmembrane protein structure (found in red blood cells):

A
  1. glycophorin
  2. band 3
30
Q

glycophorin is a ()-pass transmembrane protein

A

single

31
Q

band 3 is a ()-pass transmembrane protein

A

multiple

32
Q

what are the mechanisms of proteins anchored to the PM by covalently attached lipids or glycolipids

A
  1. glycosylphosphatidylinositol (GPI) anchors (outer leaflet)
  2. N-terminal myristoyl group (inner leaflet)
  3. C-terminal (cysteine residues) prenyl group or palmitoyl group (inner leaflet)
33
Q

describe the mechanism of how proteins are associated to the outer leaflet of the PM via GPI anchors

A
  • glycosylated proteins from the ER are initially associated with the plasma membrane through their C-terminus
  • C-terminus is cleaved and exchanged for GPI anchor → protein is associated to PM only through glycolipid anchor
34
Q

describe the mechanism of how proteins are associated to the inner leaflet of the PM via the addition of an N-terminal myristoyl group

A
  • addition of myristic acid (14 C fatty acid) to N terminus of polypeptides synthesized by free ribosomes
35
Q

describe the mechanism of how proteins are associated to the inner leaflet of the PM via the addition of a C terminal prenyl/palmitoyl group

A
  • addition of prenyl groups (15 or 20 C fatty acid) or palmitic acid (16 Cs) to C terminus of polypeptides synthesized by free ribosomes
35
Q

carbohydrate coat formed by oligosaccharides of glycolipids and glycoproteins → covers cell surface

A

glycocalyx

36
Q

the glycocalyx is formed from:

A
  1. heavy glycosylation of the extracellular portions of transmembrane proteins in PM
  2. exposure of the carbohydrate portions of glycolipids in PM on the cell surface
37
Q

functions of the glycocalyx

A
  1. protects cell surface from ionic and mechanical stress
  2. forms a barrier to invading microorganisms
  3. oligosaccharides participate in cell-cell interactions
38
Q

regions in which the mobility of MAPs are restricted

A

plasma membrane domains

39
Q

what are the 2 distinct plasma domains of epithelial cells?

A
  1. apical domain
  2. basolateral domain
40
Q

epithelial cell PM domain that faces intestinal lumen; covered by microvilli to increase surface area → efficiently facilitates nutrient absorption

A

apical domain

41
Q

epithelial cell PM domain that faces underlying connective tissue; specialized to mediate transfer of absorbed nutrients into the circulatory system

A

basolateral domain

42
Q

restrict PM proteins to the appropriate domains of the epithelial cell surface

A

tight junctions

43
Q

motility of PM proteins can also be restricted as a result of association with the (1) or with (2) (location of lipid-protein interactions

A
  1. cytoskeleton
  2. specialized lipid domains
44
Q

() are specialized lipid domains formed by clusters of sphingomyelin, glycolipids, and cholesterol

A

lipid rafts

45
Q

the rigidity of lipid rafts is mostly due to () and its interaction with (2) to form small semisolid patches

A
  1. cholesterol
  2. sphingomyelin
46
Q

lipid rafts are enriched in (1) and (2) that are involved in various functions

A
  1. GPI-anchored proteins
  2. transmembrane proteins
47
Q

() are a subset of lipid rafts that start as invaginations in the PM; formation required high content of membrane cholesterol

A

caveolae

BS202 (36 decks)

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