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EoM > Membrane Structure > Flashcards

Membrane Structure Flashcards

1
Q

Fluid Mosaic Model

A
  • fluid phospholipid bilayer with proteins embedded
    Evidence:
    -Lipid bilayer, biochemical and EM evidence from RBC plasma membranes
    -Mosaic, freeze fracture
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2
Q

Membrane Composition

A

-Lipid - bilayer
Protein - peripheral and integral
Carbohydrate - linked to lipid or protein
- proportion of lipid and protein depends on function of membrane

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3
Q

Composition: Lipids and Protein

A

Myelin sheath - 82% lipid, 18% protein

Mitochondrial inner membrane - 24% lipid, 76% protein

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4
Q

Lipid Composition

A
  • three membrane lipid types ( phospholipids, cholesterol, glycolipids)
  • amphipathic
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5
Q

Glycolipids composition

A
  • carbohydrate
  • neutral glycolipids - cerebrosides and globosides
  • one or more uncharged sugar residues
  • blood group determinants (ABO system)
  • Carbohydrate:
  • Gangliosides: complex oligosaccharides, one or more sialic acid residues ( has net (-) charge), errors in metabolism cause lysosomal storage diseases such as Tay-Sachs and Gaucherie where Gangliosides accumulate in the brain
  • pattern of sugar residues is variable
  • always in outer leaflet of cell membrane and inner leaflet of organelles, contribute to glycocalyx
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6
Q

Glycocalyx

A
  • fuzzy coat on external surface
  • carbohydrate residues on glycolipids and glycoproteins
  • protects GI membranes from digestion
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7
Q

Peripheral Proteins

A
  • non-covalent bonds with protein or lipids (H bonds, or ionic interaction)
  • Removed by high salt or extreme pH
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8
Q

Integral Membrane proteins

A
  • embedded in lipid bilayer
  • removed by detergent
  • Three types: single leaflet, single pass transmembrane, multiple pass transmembrane
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9
Q

Single Leaflet Integral proteins

A
  • lipid is covalently bound to single AA
  • Outer leaflet: GPI anchor
  • Inner leaflet:
  • Fatty acid: Myristic acid is added to N-terminal Gly, Palmitic acid added to internal Cys
  • Long Chain hydrocarbons: prenyl group is aged to a C-terminal Cys, Farnesyl-Lamins, Geranylgeranyl - small moneomeric GTPases
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10
Q

Alpha-helical transmembrane Proteins

A
  • transmembrane domain: single pass and multipass

- Extracellular (glycosylated) and cytoplasmic domains

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11
Q

Single Pass Transmembrane Proteins

A
  • hydrophobic alpha-helix in membrane

- polar domains on both sides of membrane

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12
Q

Multipass Transmembrane Proteins

A
  • alternating stretches of hydrophobic and hydrophilic AA
  • hydrophobic regions form the multiple transmembrane domains
  • hydrophilic regions form the polar intracellular and extracellular domains
  • can make aqueous channels in membranes
  • side chains are arranged so that hydrophobic ones contact lipid, hydrophilic ones surround the central opening
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13
Q

Membrane Properties

A
  • asymmetry
  • fluidity
  • specialized domains
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14
Q

Asymmetry

A
  • distribution of lipids not the same in both halves of the bilayer
  • proteins have specific orientation (extracellular and cytoplasmic domains)
  • Glycocalyx - carbohydrate on outside
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15
Q

External leaflet has more

A
  • phosphatidylcholine, sphingomyelin, glycolipids
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16
Q

Internal leaflet has more

A

Phosphatidylserine, phophatidylethanolamine, phosphatidylinositol

17
Q

Asymmetric Orientation of Transmembrane proteins

A

-orientation of proteins, functional portions of proteins are oriented on either the extracellular or cytoplasmic side of the membrane
Receptors - ligand binding domain will be on outside of membrane, effector portion will be on the cytoplasmic side of the membrane where it can transmit a signal to the cell

18
Q

Motion of lipids in membranes

A
  • rotate in place
  • hydrophobic tails flex
  • flip flop across membrane (phospholipids rare, cholesterol common)
  • lateral movement
19
Q

Fluidity

A
  • movement of lipids in the membrane
  • Depends on: temp, lipid composition
  • lipid disordered = more fluid
  • Lipid ordered = less fluid
20
Q

Affect of Lipid Composition on Fluidity

A
  • shorter fatty acid chains make membrane more fluid
  • unsaturated phospholipids with bend in tail make membranes more fluid
  • cholesterol with rigid steroid rings - decrease fluidity at high temp, increase fluidity at low temp to prevent freezing
21
Q

Protein Mobility

A
  • proteins can move within membrane (rotate, lateral diffraction)
  • experimental evidence for mobility of membrane proteins (cell fusion)
22
Q

Cell Fusion Experiment

A
  • Antibodies to human and mouse membrane proteins tagged with fluorescent dyes
  • cells fused and antibodies added
  • initially proteins separate
  • diffuse evenly over time
23
Q

Membrane Domains

A

1) epithelial cell
2) Domains:
- apical - faces lumen or external surface
- basolateral - faces internal side of tissues and adjacent cells
3) maintained by tight junctions
4) restricts proteins to specific regions
- important functional implications
5) some proteins are restricted to specific membrane domains
6) location serves function

24
Q

Lipid Rafts

A

Microdomains that are enriched in: sphingolipids containing saturated, long chain fatty acids, cholesterol, GPI-linked and acyl acted proteins

1) Regional differences in fluidity
- composition makes rafts less fluid
- restrict movement of proteins
2) important for signal transduction
- receptor dimerization
- association with effector molecules

EoM (17 decks)

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