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Cell and Molecular Biology > Module 2A Membrane Structure > Flashcards

Module 2A Membrane Structure Flashcards

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1
Q

encloses the cell, defines its boundaries, maintains essential differences between the cytosol and the extracellular environment, and supports ion gradients, protein sensors/receptors, and membrane proteins.

A

plasma membrane

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2
Q

What is the basic structural component of all cell membranes?

A

lipid bilayer

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3
Q

How much of the mass of animal cell membranes is made up of lipids?

A

50%

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4
Q

What property makes lipid molecules suitable for membrane formation?

A

amphiphilic - contain both hydrophobic and hydrophilic regions.

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5
Q

the most abundant membrane lipids, with a hydrophilic head and two hydrophobic hydrocarbon tails, forming the core of the lipid bilayer.

A

phospholipids

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6
Q

create kinks in the hydrophobic tail, which increases fluidity and prevents tight packing in the lipid bilayer.

A

cis-double bonds

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7
Q
  • It is the main phospholipids.
  • They have a three-carbon glycerol backbone, two long-chain fatty acids, and 3rd carbon is attached to a phosphate group linked to a head group.
A

phosphoglycerides

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8
Q

What is the main structure of phosphoglycerides? (3)

A
  • three-carbon glycerol backbone
  • two long-chain fatty acids
  • 3rd carbon is attached to phosphate group linked to a head group.
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9
Q

Name three major types/classes of phosphoglycerides (most abundant ones in mammalian cell membranes and derived from glycerol)

A
  • Phosphatidylethanolamine
  • phosphatidylserine
  • phosphatidylcholine
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10
Q
  • Another important class of phospholipids derived from sphingosine rather than glycerol.
  • derived from sphingosine, which includes a long acyl chain, an amino group, and two hydroxyl groups.
A

sphingolipids

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11
Q

Sphingolipids are derived from __, which includes a __, an __, and two __.

A
  • sphingosine
  • long acyl chain
  • amino group
  • hydroxyl groups
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12
Q

What is the most common type of sphingolipid?

A

sphingomyelin

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13
Q

Sphingomyelin has a __ attached to the amino group and a __ attached to the terminal hydroxyl group.

A
  • fatty acid tail
  • phosphocholine group (a simple molecule containing a choline group bonded to a phosphate group)
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14
Q

resemble sphingolipids but have sugars attached, often contributing to cell recognition and protection.

A

glycolipids

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15
Q

a sterol with a rigid ring structure, a single polar hydroxyl group, and a short nonpolar hydrocarbon chain. It helps modulate membrane fluidity and stability.

A

cholesterol

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16
Q

Phospholipids spontaneously form bilayers in aqueous environments due to their __ nature. Phospholipid molecules spontaneously __ to bury their __ tails, forming bilayers where tails are shielded inside, away from water.

A
  • amphiphilic
  • aggregate
  • hydrophobic
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17
Q

structures with hydrophobic tails inward, formed when amphiphilic molecules aggregate in water at certain concentrations or conditions.

A

spherical micelles

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18
Q

Lipid bilayers have a __ where any small tear causes lipids to rearrange spontaneously to eliminate the free edge, often closing to form a sealed compartment.

A

self-sealing property

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19
Q

synthetic (artificial) lipid bilayers, which can be made in the form of spherical vesicles.

A

liposomes

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20
Q

How can the motion of individual lipid molecules in a bilayer be measured?

A

Fluorescence Recovery after Photobleaching (FRAP)
By constructing a lipid molecule with a fluorescent dye or small gold particle attached to its polar group, allowing observation of its diffusion.

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21
Q

like =N-O, is a modified lipid head group containing an unpaired electron. It produces a paramagnetic signal detected by electron spin resonance (ESR) to study lipid motion.

A

spin label

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22
Q

A spin label, like =N-O, is a modified lipid head group containing an unpaired electron. It produces a paramagnetic signal detected by __ (__) to study lipid motion.

A

electron spin resonance (ESR)

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23
Q

the rare migration of phospholipid molecules from one monolayer of a bilayer to the other.

A

flip-flop

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24
Q

It’s the quick exchange of places among lipid molecules within the same monolayer of a bilayer, allowing for membrane fluidity.

A

rapid lateral diffusion

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25
Q

What gives lipid molecules flexibility and rapid movement in the bilayer? (2)

A
  • flexibility of hydrocarbon chains
  • the rapid rotation of lipid molecules around their long axis
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26
Q

enzymes that catalyze the rapid flip-flop of phospholipids between monolayers in the lipid bilayer.

A

phospholipid translocators (flippases)

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27
Q

How does the composition of a lipid bilayer influence its fluidity? (2)

A
  • lipid composition
  • temperature
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28
Q

a change from a liquid state to a two-dimensional rigid crystalline state at a characteristic temperature

A

phase transition

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29
Q

enhances the permeability barrier, decreases deformability, and prevents hydrocarbon chains from crystallizing, modulating bilayer properties.

A

cholesterol

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30
Q

Archaeal bilayers are built from ______, differing in molecular design from those in most prokaryotes and eukaryotes.

A

20–25-carbon-long prenyl chains

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31
Q

Eukaryotic plasma membranes are highly varied, containing __ different lipid species, more diverse than those of prokaryotes and archaea.

A

500-200

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32
Q

specialized membrane microdomains that organize signaling molecules, influence membrane fluidity and protein trafficking, and regulate processes like neurotransmission and receptor trafficking.
- highly ordered and tightly packed lipid molecules
- contain high levels of sphingolipids, including gangliosides and cholesterol.

A

Lipid rafts

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33
Q

What process causes certain lipids to come together in separate membrane domains?

A

phase segregation

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34
Q
  • store lipids within the cell
  • surrounded by a single phospholipid monolayer that contains a variety of proteins.
A

lipid droplets

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35
Q

What types of cells are specialized for lipid storage?

A

fat cells/adipocytes

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36
Q

What kind of lipids form the contents of lipid droplets? (2)

A

Triacylglycerols and cholesterol esters, which are neutral and hydrophobic

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37
Q

What structure surrounds lipid droplets?

A

a single phospholipid monolayer that contains a variety of proteins.

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38
Q

Under what condition do lipid droplets form rapidly in cells?

A

when cells are exposed to high concentrations of fatty acids.

39
Q
  • refers to the difference in composition between the two monolayers of a lipid bilayer.
  • important for converting extracellular signals into intracellular responses.
A

lipid asymmetry

40
Q

What lipids are primarily found in the outer monolayer of red blood cells (RBCs)? (2)

A
  • phosphatidylcholine
  • sphingomyelin
41
Q

What lipids are primarily found in the inner monolayer of red blood cells (RBCs)? (2)

A
  • phosphatidylethanolamine
  • phosphatidylserine.
42
Q

Which proteins bind to specific lipid head groups in the cytosolic monolayer? (An example)

A

protein kinase C (PKC)

43
Q

serves as a lipid kinase for signaling pathways, specifically involving phosphoinositide 3-kinase (PI 3-kinase).

A

Phosphatidylinositol (PI)

44
Q

cleave an inositol phospholipid to generate two fragments, one that activates protein kinase C and another that stimulates the release of Ca²⁺ from the endoplasmic reticulum.

A

Phospholipases C

45
Q

Phospholipases C cleave an __ to generate two fragments, one that activates __ and another that stimulates the release of __ from the endoplasmic reticulum.

A
  • inositol phospholipid (or phosphatidylinositol)
  • protein kinase C
  • Ca²⁺
46
Q

Animals use phospholipid asymmetry to distinguish between live and dead cells. Animals exploit phospholipid asymmetry by detecting the translocation of __ from the inner to the outer monolayer during apoptosis.

A

phosphatidylserine

47
Q
  • sugar-containing molecules found in cell membranes.
  • exclusively found in the outer monolayer of the lipid membrane.
  • most extreme asymmetry in their membrane distribution
A

glycolipids

48
Q

The asymmetric distribution of glycolipids results from the __ of __ groups to __ molecules in the __ of the Golgi apparatus.

A
  • addition
  • sugar
  • lipid
  • lumen
49
Q

Glycolipids are present in all __ plasma membranes and some __ membranes, making up about __ of the membrane composition.

A
  • eukaryotic
  • intracellular
  • 5%
50
Q

The function of glycolipids is influenced by their __, providing specific roles in cell recognition and protection.

A

localization

51
Q

In __ cells, glycolipids on the exposed apical surface may help protect the membrane against harsh conditions.

A

epithelial

52
Q

are charged glycolipids that have significant electric effects and are important for cell-to-cell recognition.

A

gangliosides

53
Q

provide entry points for certain bacterial toxins and viruses, aiding in their ability to infect cells.

A

glycolipids

54
Q

perform most of the membrane’s specific tasks, giving each type of cell membrane its characteristic functional properties.

A

membrane proteins

55
Q

The amounts and types of proteins in a membrane are __.

A

highly variable

56
Q
  • can function on both sides of the bilayer or transport molecules across the membrane.
  • have a unique orientation, with different functions in their cytosolic and noncytosolic domains.
A

transmembrane proteins

57
Q

Lipid anchors: Proteins that function on only one side of the lipid bilayer are often associated exclusively with either the __ or a __ on that side.

A
  • lipid monolayer
  • protein domain
58
Q

control the membrane localization of some signaling proteins, helping to keep them attached to specific membrane regions.

A

lipid anchors

59
Q

The __ of a polypeptide chain is formed into an α helix, contacting the hydrophobic area of the lipid bilayer.

A

membrane-spanning segment

60
Q

Proteins that have a polypeptide chain that crosses the membrane only once.

A

single-pass transmembrane proteins

61
Q

have multiple transmembrane strands of a polypeptide chain arranged as a β sheet rolled up into a cylinder.

A

Multipass transmembrane proteins

62
Q

are used to localize potential α-helical membrane-spanning segments in a polypeptide chain.

A

hydropathy plots

63
Q

What is estimated about the proportion of transmembrane proteins in an organism?

A

about 30%

64
Q

Where are oligosaccharide chains located in relation to membrane proteins?

A

noncytosolic side of the membrane.

65
Q

bonds that form on the noncytosolic side to help stabilize the folded structure of the polypeptide chain or its association with other polypeptides.

A

Disulfide bonds

66
Q

extensively coat the surface of all eukaryotic cells.

A

carbohydrates

67
Q

are small amphiphilic molecules that are more soluble in water than lipids, with a polar side that can be ionic (like sodium dodecyl sulfate) or nonionic (like octylglucoside and Triton).

A

detergents

68
Q

What is necessary to solubilize and purify membrane proteins?

A

detergents

69
Q

Give examples of ionic (1) and nonionic detergents (2)

A

ionic
- SDS (sodium dodecyl sulfate)
nonionic
- Octylglucoside
- Triton

70
Q

the surfactant concentration at which micelle formation is first seen in the solution.

A

Critical micelle concentration (CMC)

71
Q

When mixed with membranes, the __ ends of detergents bind to the __ regions of membrane proteins, displacing __ molecules with a __ of detergent molecules.

A
  • hydrophobic
  • hydrophobic
  • lipid
  • collar
72
Q

allow for the reconstitution of functionally active membrane protein systems from purified components, enabling the analysis of activities of membrane transporters, ion channels, signaling receptors, etc.

A

Mild detergents

73
Q

are small, uniformly sized patches of membrane surrounded by a belt of protein that covers the exposed edge of the bilayer to keep the patch in solution.

A

nanodiscs

74
Q

How can nanodiscs be analyzed structurally?

A

by single particle electron microscopy techniques

75
Q

Membrane proteins often function as part of __.

A

multicomponent complexes

76
Q

captures light energy and uses it to pump H+ across the membrane.

A

photosynthetic reaction center

77
Q

Do membrane proteins flip across the lipid bilayer?

A

No

78
Q

Membrane proteins can __ about an axis perpendicular to the plane of the bilayer and move laterally within the membrane (__).

A
  • rotate
  • lateral diffusion
79
Q

What technique measures the lateral diffusion rates of membrane proteins?

A

Fluorescence recovery after photobleaching (FRAP)

80
Q

involves labeling individual membrane molecules and tracking their movement by video microscopy.

A

single-particle tracking

81
Q

Most cells confine membrane proteins to specific regions within the membrane. In epithelial cells, certain plasma membrane enzymes and transport proteins are confined to the __, while others are confined to the __ and __. (ex. lipid rafts)

A
  • apical surface
  • basal; and
  • lateral surfaces
82
Q

The __ distribution of membrane proteins is often essential for the function of the epithelium.

A

asymmetric

83
Q

What creates barriers that confine proteins in epithelial cells?

A

Barriers set up by specific types of intercellular junctions

84
Q
  • interactions in that membranes create nanoscale raft domains that function in signaling and membrane trafficking.
  • Within lipid rafts, this interaction promotes signal transduction and cellular responses.
A

Protein-protein interactions

85
Q

Cells that create lipid rafts enriched in cholesterol and proteins, facilitating efficient signaling and membrane trafficking, which enhance motility and the acrosome reaction for fertilization.

A

Sperm cells or mammalian spermatozoon

86
Q
  • gives membranes mechanical strength and restricts membrane protein diffusion
  • It forms mechanical barriers that obstruct the free diffusion of proteins within the membrane.
A

cortical cytoskeleton

87
Q

What is the primary component of the cytoskeleton that gives red blood cells their characteristic biconcave shape?

A

Spectrin

88
Q
  • long, thin, flexible rod
  • a filamentous protein, forms a meshwork that maintains the structural integrity and shape of the plasma membrane.
A

Spectrin

89
Q
  • It provides mechanical strength, allowing red blood cells to withstand stress and deform as they pass through narrow capillaries.
  • It is a deformable, netlike meshwork that covers the entire cytosolic surface of the red cell membrane.
A

spectrin-based cytoskeleton

90
Q

What happens to red blood cells with genetic abnormalities in spectrin? (3)

A

cells become:
- anemic;
- spherical; and
- fragile
due to the lack of structural integrity.

91
Q

What processes are influenced by membrane-bending proteins that deform bilayers? (3)

A
  • Vesicle budding
  • cell movement
  • cell division
92
Q

The shape is controlled dynamically by the __ and __ forces exerted by __ or __ structures.

A
  • pushing
  • pulling
  • cytoskeletal
  • extracellular
93
Q

They facilitate the deformation of lipid bilayers, which is essential for various cellular processes like vesicle formation and cell motility.

A

membrane-bending proteins

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