membranes Flashcards

1
Q

briefly describe some of the functions of a cell membrane

A
  • flexibility accomodates cell growth and movement
  • provides compartmentalization
  • fusion (endo and exocytosis), slitting (mitosis)
  • selective permeability determines what goes in/out of cell
    -makes it easier for processes like signaling to occue
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2
Q

what is meant by “sidedness”?

A
  • the inner and outer leaflets have different lipid composistions
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3
Q

is the lipid makeup of the membrane static?

A
  • no, can change based on cell compartment and organism
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4
Q

list three functions of proteins in membranes

A
  • receptors, enzymes, transport, adhesion
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5
Q

name 2 types of integral membrane proteins (i.e. how they are connected to the membrane

A
  1. polytopic- spans cell membrane multiple times
  2. monotopic - anchroed to only one side of the membrane
  3. bitopic - spans the lipid bilayer only once
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6
Q

what is a peripheral membrane protein

A
  • they associate noncovalently with membrane components
  • associated to proteins or lipid heads
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7
Q

how do you interpret a hydropathy plot and how can it predict transmembrane segments

A
  • calculates the average hydropathy index for a window of a certain size
  • the hydrophobic regions are typically transmembrane segments
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8
Q

why can beta barrels extend through a membrane while a beta sheet cannot?

A
  • the beta barrel can hide the hydrophilic regions on the inside while the hydrophobic regions face outward towards the hydrophobic lipids
  • sheets cannot hide hydrophilic regions like this
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9
Q

what are lipid rafts and what components are they enriched in?

A
  • less fluid microdomains of the plasma membrane
    -enriched in cholesterol and sphingolipids with a long saturated fatty acid chain
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10
Q

what is the difference between lateral diffusion and transverse diffusion of a membrane lipid? which requires energy and why?

A
  • lateral diffusion - molecules move sideways, changing places with neighboring lipids
  • transverse diffusion - lipid moves from one side of the bilayer to the other
  • necessary to maintain sidedness
  • ## transverse requires ATP to move one lipid, but not to move two at the same time
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11
Q

what is one possible function of lipid rafts?

A
  • localize molecules involved in a cartain pathway near each other
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12
Q

what is Fluorescence Recovery After Photobleaching (FRAP)

A
  • attachment of probes to head groups of lipids
  • bleach small area with a laser beam to make it nonfluorescent
  • see how long it takes for the labeled lipid molecules to diffuse into the bleached region to get diffusion rate
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13
Q

do all proteins have the ability to diffuse laterally? why or why not?

A
  • no, many are attached to the cytoskeleton, which limits their movement
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14
Q

passive diffusion of polar molecules through a membrane has a high activation barrier, why?

A
  • the middle of the bilayer is very nonpolar so it takes a lot of energy to get a polar molecule through it
  • lots of energy to remove solute shell and then readd it
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15
Q

what are the 2 broad classes of proteins that help molecules cross membranes and what is a major difference between them?

A
  • channels and transporters
  • channels are basically just open highways - cannot be saturated
  • transporters can move molecules against their electrochemical gradient, transporters cannot
  • transporters can be active or passive channels are all passive
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16
Q

Define membrane potential

A
  • voltage difference across a biological membrane
  • typically negative on the inside
17
Q

what is an electrochemical gradient

A
  • defined by the combined effect of the concentration and electrical gradient across the membrane
  • drives the movement of ions
18
Q

what type of proteins are necessary to move molecules against their electrochemical gradient

A
  • active transport proteins (transporters)
  • primary expends energy, usually ATP
  • secondary couples uphill transport with a downhill transport