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BIOL 2020 > Membranes > Flashcards

Membranes Flashcards

1
Q

Size of cell membranes?

A

5-10 nm thick

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2
Q

Functions of cell membranes? (8)

A
  1. compartmentalization
  2. scaffold for biochemical activities
  3. provides selectively permeable barrier
  4. transporting solutes
  5. responding to external signals
  6. intercellular interactions
  7. intracellular interactions
  8. energy transduction
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3
Q

Composition of cell membranes (3 components)

A

lipids (bimolecular layer)
proteins
carbs–attached to lipids or proteins

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4
Q

Membrane Lipids are all…

A

ALL AMPHIPATHIC

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5
Q

Phospholipids

A

organize so that fatty acid tails face one and other and polar heads face aqueous l outside. In between the fatty acid chains is cholesterol–more = more rigid

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6
Q

If water wants to get through a membrane there must be a…

A

channel

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7
Q

Movements of lipid bilayer (3 types and associated times)

A
  1. flex 10^-9 sec
  2. lateral shift 10^-6 sec
  3. transverse diffusion (flip flop) 10^5 sec
    need flipases to move from one leaflet to the other
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8
Q

Features of lipid bilayers… (3)

A

fluid
seal spontaneously
asymmetric because lipids do not flip flop

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9
Q

Membrane carbohydrates exist as…

A

glycoproteins or glycolipids which are asymmetric and short oligosaccharides
always face away from the cytosol
important in cell-cell interactions and sorting proteins into compartments

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10
Q

Types of linkage between carbs and proteins/lipids

A

N-linked (amino–attached to nitrogen) more common

O-linked (attached to O by carboxyl) less common

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11
Q

Membrane Proteins (3 types)

A

~50% by weight
integral
peripheral
lipid anchored

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12
Q

Integral membrane proteins

A

penetrate right through lipid bilayer
asymmetric
amphipathic–hydrophobic part anchors it into the lipid bilayer really well

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13
Q

Peripheral membrane proteins

A

weakly attached by electrostatic interactions
dynamic–leave and come back
sit on edge
asymmetrical

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14
Q

Lipid anchored membrane proteins

A

Are on either side of membrane but don’t go through
Defined by being covalently attached to phospholipid (phosphotidylinositol)
lipid–carb–protein
GPI is attached to a phospholipid only on the outside of cell BUT if attached to myristate or farnesyl then can be either inside or outside and not called GPI

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15
Q

Fluid mosaic model

A

defines characteristics of cell membrane
fluid–dynamic, there is movement
quasifluid–movement is somewhat restricted
mosaic–asymmetrical, little bit patchy because no flip flop

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16
Q

Example of how phospholipids are asymmetrically distributed

A

Polar head defines the phospholipid
PC almost exclusively on outside
PE almost exclusively on inside

17
Q

Technique to study membrane protein mobility

A

FRAP

18
Q

Five types of protein movement

A
  1. Random (not much restriction)
  2. No movement ever–completely stuck
    FRAP, colours never come back
  3. Defined direction of movement
    because being carried along cytoskeleton by motor proteins
  4. No movement (immobilized)
    because swarmed by other transmembrane proteins corralled around it
  5. Random movement that is restricted
    has to stay within constrains (likely due to cytoskeleton)
19
Q

How did they prove that proteins are sometimes anchored by the extracellular matrix?

A

Removed cytoplasmic portion of protein

  • Found that they sometimes stayed stuck and other times were free to move
    eg: acetycholine receptor at neuromuscular junction
20
Q

Lipid Rafts

A

Microdomains within the the cellular membrane that posses decreased fluidity due to the presence of cholesterol, glycolipids, and phospholipids containing longer saturated fatty acids

21
Q

Lipid rafts 3 features

A
  1. tightly packed (high [saturated fat]
  2. high [sphingolipids]
    sphingolipid=no glycerol backbone, long fatty acid tail
  3. A lot of cholesterol (rigidity)
22
Q

Lipids rafts have a lot of…

A

GPI anchored proteins and signaling proteins

23
Q

Experiment showing that diffusion is limited for other lipds

A

lipid labelled with gold particle get tracings, find that moves randomly but in one area– in cell membrane. If done in an artificial membrane movement not restricted at all

24
Q

Why are red blood cells good for studying the plasma membrane?

A

Because they have no nucleus and not a lot of other organelles
Found spectrin which gives a membrane its shape (holds it–biconcave in this case)

BIOL 2020 (4 decks)

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