L9. Membrane structure & function Flashcards

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1
Q

how does the plasma membrane act?

A
  • as a selective barrier
  • as a means of information relay
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2
Q

plasma membrane - selective barrier

A
  • separates cell form its surroundings
  • enables cells to differ from its environment
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3
Q

plasma membrane - information relay

A
  • receiving information using receptor proteins
  • import and export of small molecules using transport proteins
  • capacity for movement and expansion
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4
Q

explain membrane composition

A
  • all membranes are composed of lipids and proteins
  • the lipids are arranged in two closely apposed sheets forming a lipid bilayer
  • this bilayer serves as a permeability barrier to most water-soluble molecules
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5
Q

membrane composition - lipids

A
  • each lipid has a hydrophilic head and a hydrophobic tail
  • thus are known as amphipathic
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6
Q

membrane composition - phospholipids

A

lipids that have a phosphate-containing hydrophilic head linked to a pair of hydrophobic tails

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7
Q

phospholipids - hydrophobicity and hydrophilicity

A
  • the hydrophobic tails are insoluble in water bc they are uncharged and nonpolar
  • the hydrophilic heads dissolve readily in water bc they are charged and polar
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8
Q

explain the spontaneous closing of the bilayer

A

because of the phospholipids hydrophobic and hydrophilic properties it is energetically favorable for the molecules to create the bilayer

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9
Q

spontaneous closing of phospholipid bilayer - what are liposomes

A

they are pure phospholipids that forms closed spherical vesicles when added to water

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10
Q

what does the fluidity of the phospholipid bilayer depend on

A
  • hydrocarbon tail lengths
  • saturation
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11
Q

fluidity of phospholipid bilayer - hydrocarbon tail length

A
  • longer tails interact more and makes the membrane less fluid
  • shorter tails interact less and makes the membrane more fluid
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12
Q

fluidity of phospholipid bilayer - saturation

A
  • unsaturated tail = has kinks (double bonds present) = more fluid
  • saturated tail = has no kinks (no double bonds present) = less fluid
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13
Q

phospholipid fluidity - bacteria and yeast

A
  • they are able to modify the conditions with temperature
  • higher temp = longer tails and fewer double bonds = less fluid
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14
Q

what do scramblases do

A

they are enzymes that randomly transfer phospholipid molecules from one monolayer to the next

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15
Q

scramblases - where are they located and when are they used

A
  • located in ER membrane
  • used when phospholipid synthesis adds new phospholipids to the cytolytic side of the bilayer
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16
Q

what do flippases do?

A

they are enzymes that catalyzes the transfer of specific phospholipids to the cytolytic monolayer

17
Q

flippases - where are they located and when are they used

A
  • located in Golgi membrane
  • used when membranes leave the ER and are incorporated into the Golgi
18
Q

flippases - how is it important for apoptosis (cell death)

A
  • When a cell is undergoing programmed cell death, flippases stops working
  • PS (Phosphatidylserine) goes up the bilayer instead of staying at the bottom (inner leaflet)
  • When PS (Phosphatidylserine) is detected the cell is cleaned up by macrophages
19
Q

what is the role of cholestrol

A
  • stiffens the bilayer by filling the spaces made by unsaturated kinks
  • can impact fluidity based on temperature
  • facilitates lipid-raft formation
20
Q

cholesterol - how is fluidity impacted by temperature

A
  • at high temp: reduces fluidity and permeability
  • at low temp: reduces crystallization and maintains fluidity
21
Q

cholesterol - what is the lipid-draft formation

A
  • they are pockets where there is more cholesterol packed and has phospholipids with longer tails
  • they have a longer region of hydrophobicity so proteins can have longer transmembrane domains
22
Q

explain alpha-helical transmembrane proteins

A
  • hydrophobic side chains of alpha-helix contact the hydrophobic hydrocarbon chains of the phospholipid molecules
  • hydrophilic parts of the alpha-helix form hydrogen bonds with one another on the inside of the helix
23
Q

explain how membrane proteins can be extracted

A
  • with detergents
  • when mixing membranes and detergent together, hydrophobic ends of the detergent interacts with hydrophobic regions of transmembrane proteins
  • this disrupts the lipid bilayer and separates most proteins from the phospholipids
23
Q

explain beta-barrel transmembrane proteins

A
  • they roll up into a cylinder
  • hydrophilic side chains will face the inside of the barrel
  • hydrophobic portion will contact the core of the bilayer
24
Q

what is the cell cortex

A
  • it is a fibrous protein meshwork that stabilizes animal cells
  • it is rich in actin (used for structure) and myosin (used for movement)
25
Q

how can the plasma membrane’s mobility be restricted

A
  • lateral mobility restriction
  • tight junctions
26
Q

restricting plasma membrane mobility - lateral mobility restriction

A
  • proteins can be tethered to:
    1. the cell cortex inside the cell
    2. to extracellular matrix molecules
    3. to proteins on the surface of another cell
27
Q

restricting plasma membrane mobility - tight junctions

A
  • a barrier formed along the line where a cell is sealed to adjacent cells
  • creates a seal between the plasma membranes and the proteins cannot diffuse past the junction
28
Q

what is the glycocalyx

A
  • a sugar coating on the outside of the cell
  • the coat is connected to the transmembrane proteins
  • its purpose is to help protect the cell surface from mechanical damage