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Cell Bio > Cell Membranes & Membrane Proteins > Flashcards

Cell Membranes & Membrane Proteins Flashcards

1
Q

what are cell membranes composed of

A
  • phospholipid bilayer
  • other lipids
  • embedded proteins
  • associated carbohydrates
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2
Q

what is the role of the lipid sheets in cell membranes

A
  • prevents molecules on one side from freely mixing w the other
  • acts as selective barriers
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3
Q

how do cell membranes act as selective barriers

A
  • keep cell components separate form the environment
  • compartmentalize intracellular space and enclose reactions
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4
Q

what vital functions are cell membranes involved in

A
  • communication w the environment
  • import and export of materials
  • flexibility for growth and movement
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5
Q

the membrane surrounding a cell is referred to as what

A

the plasma membrane

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6
Q

internal membranes within a cell form specialized compartments called what

A

organelles

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7
Q

is the phospholipid bilayer thin or thick

A
  • thin
  • ~5nm
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8
Q

what is the primary molecule in cell membranes

A

phospholipids

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9
Q

describe the structure of phospholipids

A
  • polar hydrophilic head
  • 2 nonpolar hydrophobic hydrocarbon tails
  • a molecule of glycerol
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10
Q

what key characteristic of phospholipids is allowed by its structure

A

amphipathic characteristic

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11
Q

what is the most common phospholipid in membranes

A

phosphatidylcholine

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12
Q

describe the tail of phospholipids

A
  • fatty acid
  • hydrocarbon chain with a carboxyl group at one end
  • can be saturated or unsaturated
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13
Q

what happens if there is a double bond in one of the hydrophobic tails

A

makes it unsaturated

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14
Q

what does phosphatidyl refer to

A

the phosphate-glycerol-fatty acid portion of the molecule

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15
Q

describe the specific structure of phosphatidylcholine

A
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16
Q

how do membrane components form a relatively stable membrane

A
  • amphipathic nature which forms the bilayer
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17
Q

what happens to amphipathic phospholipids in water

A

form a bilayer

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18
Q

describe the relationship between amphipathic molecules and their exposed edges

A
  • exposed edges are energetically unfavourable
  • so they assemble into self-sealing containers without exposed edges (like a sphere)
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19
Q

what is formed when pure phospholipids are added to an aqueous environment

A

small spherical liposomes

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20
Q

what structures are studied to understand cell membranes and applications

A

small spherical liposomes

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21
Q

what were used to deliver mRNA COVID vaccines

A

lipid nanoparticles (similar to liposomes but with more complex structure)

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22
Q

how does the lipid bilayer behave

A

like a 2D fluid

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23
Q

how does a lipid bilayer behave as a 2D fluid

A
  • phospholipids are flexible
  • can move// change position relative to one another
  • spontaneous movement form one layer to another is rare
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24
Q

what influences cell membrane fluidity

A
  • density
  • hydrocarbon tail length (14-24 C atoms)
  • presence and number of double bonds (saturated vs unsaturated)
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25
Q

what does the fluid mosaic model show

A

other components of the membrane can diffuse laterally through the fluid lipid phase

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26
Q

what role does cholesterol play in membranes

A
  • inserted among phospholipids to help stiffen and stabilize the membrane
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27
Q

what are the benefits related to cholesterol integration into cell membranes

A
  • selective
  • permeable
  • strength
  • stability
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28
Q

are membranes symmetrical

A

no (different phospholipids are found on the inside and outside layers of the membrane)

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29
Q

where is phosphatidycholine primarily found

A

non-cytosolic layer

30
Q

where is sphingomyelin primarily found

A

non-cytosolic layer

31
Q

where is phosphatidylserine primarily found

A

cytosolic layer

32
Q

where is phosphatidylethanolamine primarily found

A

cytosolic layer

33
Q

where is phosphatidylinositol primarily found

A

concentrated in cytosolic layer

34
Q

where is glycolipids primarily found

A

exclusively in non-cytosolic layer

35
Q

where does membrane assembly begin

A

in the endoplasmic reticulum

36
Q

how are new phospholipids added to the bilayer

A
  • enzymes associated w the cytosolic surface of the ER use free fatty acids
  • they are added exclusively to the cytosolic half of the bilayer
  • scramblase transfers random phospholipids from one monolayer to another
37
Q

is all of the newly formed membrane distributed throughout the cell

A
  • no
  • some remains in the ER
38
Q

where can additional asymmetrical modifications be made to the membrane

A

golgi apparatus

39
Q

how does the golgi apparatus make modifications

A
  • uses flippase to catalyze the transfer of specific phospholipids to cytosolic monolayer
  • maintains membrane characteristics in animal cells
40
Q

what is flippases

A

phospholipid-handling transporter found in the golgi apparatus membrane

41
Q

how is asymmetry in membranes maintained

A

by moving by a provess of budding and fusing

42
Q

what is the role of lipid rafts

A

concentrated sites of signaling and receptor molecules

43
Q

what is different about the structure of raft regions in a membrane

A
  • higher proportion of cholesterol and sphingolipids
44
Q

where are lipid rafts found

A

small portions of the non-cystolic layer of the membrane

45
Q

how much of animal cell membranes’ mass are made up of proteins

A

~ 50%

46
Q

what are some different kinds of membrane proteins

A
  • transporters
  • ion channels
  • anchors
  • receptors
  • enzymes
47
Q

what are transmembrane proteins

A
  • extend through the bilayer
  • part of their mass on either side
  • amphipathic (both hydrophobic and hydrophillic regions)
  • hyrdophobic regions are inside the bilayer, hydrophillic are exposed to the aqueous regions on either end
48
Q

what are monolayer-associated proteins

A
  • located almost completely in the cytosol
  • associated with the cytosolic half of the lipid bilayer
49
Q

what are lipid-linked proteins

A
  • lie entirely outside the bilayer (on one side or another)
  • attached to the membrane by a lipid group
50
Q

what are protein-attached proteins

A
  • bound indirectly to one face of the membrane or the other
  • held in place by other membrane proteins
51
Q

describe the backbone of a polypeptide chain

A
  • hydrophilic
  • forms alpha helices
52
Q

what determines the function of integral proteins

A

protein structure

53
Q

how many times do integreal proteins cross the bilayer

A
  • many cross once
  • some are comprised by a series of helices that cross the bilayer several time
54
Q

can integral proteins form beta sheets

A
  • sometimes, but less common
  • forms large aqueous pores
55
Q

when do integral proteins form beta sheet

A
  • in some bacteria and mitochondria
  • to allow passage of small nutrients, metabolites, and ions, but not large molecules
56
Q

do we know the complete structure of most membrane proteins

A
  • nope
  • relatively few are known
57
Q

why don’t we know the complete structure of many membrane proteins

A

they’re difficult to isolate and study

58
Q

what are some recent advances for investigation of membrane proteins

A
  • x ray crystallography
  • cyro-electron microscopy
  • modelling
59
Q

membrane-associated proteins play a central role in what aspect of the cell

A
  • shape and integrity
60
Q

the flattened shape in RBC is maintained by what

A
  • spectrin
  • a dimeric protein that forms a lattice
61
Q

how is the membrane stabilized in animal cells

A

by a meshwork of filamentous proteins called cell cortex

62
Q

protein movement may be restricted by what

A
  • attachment to the cortex
  • attachment to molecules outside the cell
  • cell junctions
  • diffusion barriers
63
Q

restrictions on protein movement have what function

A

can organize proteins and help carry out their function

64
Q

what are glycoproteins

A

short chains of sugars

65
Q

what are proteoglycans

A

long chains of sugars

66
Q

what is attached to many membrane-associated proteins

A
  • sugars covalently attached
67
Q

what is a glycocalyx

A
  • sugar coating on the outside of the plasma membrane
  • forms a physical barrier for anything trying to get in the cell
68
Q

what forms the glycocalyx

A
  • glycolipids
  • glycoproteins
  • proteoglycans
  • located on the non-cytosolic side of the membrane
69
Q

what do surface carbohydrates do

A
  • protect and lubricate the cells
  • play a key role in cell-cell recognition and adhesion
70
Q

what binds specific oligosaccharide side chains

A

transmembrane proteins called lectins

71
Q
A

Cell Bio (11 decks)

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