Lecture 5: Membrane Structure Flashcards

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1
Q

State 3 functions of the plasma membrane

A

1- Import and export of molecules.
2- receiving information.
3- expansion.

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2
Q

nutrients pass _______ the plasma membrane and waste products pass _______ the plasma membrane.

A

inward and outward.

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3
Q

The plasma membrane serves and prevents

A
  • barrier that separates in the interior of the cell from the surrounding medium.
  • prevents contents of the cell from escaping and mixing with the surrounding medium.
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4
Q

Some proteins in the plasma membrane act as

A

sensors in the plasma membrane to enable cell to respond to changes in its environment.

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5
Q

How does the plasma membrane expand?

A

when the cell grows or changes shape, the plasma membrane enlarges its area by adding new membrane while deforming without tearing.

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6
Q

The membranes that surround the organelles of cells

A

separate one aqueous phase (cytosol) from another (interior of organelle).

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7
Q

Internal membranes serve as

A

selective barriers.

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8
Q

membrane-bound organelles (internal membranes) maintain

A

the characteristic differences in composition between these organelles.

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9
Q

Name some membrane-bound organelles

A
  • endoplasmic reticulum.
  • peroxisomes.
  • nucleus.
  • lysosome.
  • Golgi.
  • transport vesicles.
  • mitochondria.
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10
Q

General structure of cell membranes

A

lipids and proteins.

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11
Q

The lipid component of a cell membrane consists of

A

millions of lipid molecules arranged in two closely opposed sheets, forming a bilayer.

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12
Q

Properties of a single lipid molecule

A

1- hydrophilic head.

2- one or two hydrophobic hydrocarbon tails.

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13
Q

Define amphipathic molecule

A

molecules with both hydrophilic and hydrophobic properties.

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14
Q

Name five types of lipids

A
1- fatty acids. 
2- phospholipids.
3-glycerol phospholipids.
4- non-glycerol phospholipids. 
5- cholesterol.
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15
Q

A fatty acid consists of

A

a long hydrocarbon chain with a negatively charged carboxyl group.

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16
Q

Types of fatty acids

A
  • in saturated fatty acids all of the carbon atoms are bonded to a maximum number of hydrogen atoms.
  • unsaturated fatty acids contain one or more double bonds between carbon atoms, resulting in one covalent bond with hydrogen.
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17
Q

The most abundant lipid are

A

phospholipids.

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18
Q

Phospholipids consist of

A

two fatty acids linked to a polar head group.

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19
Q

In glycerol phospholipids

A
  • the two fatty acids are bound to carbon atoms in glycerol.
  • the third carbon atom is bound to a phosphate group, which is attached to another small polar molecule (radical).
20
Q

Types of small polar molecules (aminos) found in glycerol phospholipids

A

choline, serine, inositol, ethanol amine.

21
Q

The most common glycerol phospholipid in most cell membranes is

A

phosphatidylcholine.

22
Q

The net charge of small polar molecules found in phospholipids

A
  • choline and ethanol amine are neutral.

- serine and inositol are negatively charged.

23
Q

What typer of lipid is sphingomyelin?

A

non-glycerol phospholipid.

24
Q

Define the structure of non-glycerol phospholipids

A
  • contain two hydrocarbon chains linked to a polar head group formed from serine rather than glycerol.
  • the third carbon atom of serine is bound to a phosphate group which in turn is attached to choline.
25
Q

Define the structure of glycolipids

A

-consist of two hydrocarbon chains linked to a polar head group formed from serine, which is attached to a polar carbohydrate molecule.

26
Q

Type of carbohydrate molecule in glycolipids

A

glucose or galactose.

27
Q

Define the structure of cholesterol

A

-consists of four hydrocarbon rings, one hydrophobic tail and a hydroxyl hydrophilic head.

28
Q

electrostatic bonds are between

A

charged atoms with polar polar groups and polar molecules (water).

29
Q

Why are hydrophobic molecules insoluble in water

A

because of their uncharged and non polar atoms, thus cannot form bonds with polar water.

30
Q

What happens when hydrophobic molecules are immersed in water

A
  • a cage-like structure of water molecules forms around the tails, this requires energy.
  • to minimize energy cost if tails cluster together.
31
Q

Name two conflicting forces in amphipathic molecules

A

1- the heads attract water.

2- the tails shun water and aggregate together.

32
Q

How are the conflicting forces in amphipathic molecules resolved

A

this is resolved by the formation of a phospholipid bilayer- most energetically favoured state.

33
Q

Name two types of synthetic lipid bilayers

A

1- liposomes, closed spherical vesicles.

2- flat bilayers, phospholipids applied to a small hole separating two aqueous compartment.

34
Q

Three types of phospholipid mobility in lipid bilayers

A

1- lateral diffusion: lipid molecules within a monolayer exchange places.
2- rotation: lipid molecules within a monolayer rotate around their axis.
3- “flip-flop”: lipid molecules rarely flip from one monolayer to the other.

35
Q

membrane fluidity depends on

A

a- length of hydrocarbon tails.
b- level of saturation of tails with respect to hydrogen.
c- presence of sterol cholesterol.

36
Q

In what do length of hydrocarbon tails affect membrane fluidity

A
  • shorter chain increase fluidity because the distance between tails are larger (less packing).
  • length of chain is inversely proportional to membrane fluidity.
37
Q

In what way do levels of saturation affect membrane fluidity

A
  • unsaturated= more fluid, increase distance between neighbouring molecules.
  • saturated= less fluid.
38
Q

In what way do cholesterol affect membrane fluidity

A
  • the rigid hydrocarbon rings of cholesterol interact and partially immobilize the regions of fatty acid chains, therefor stiffening the bilayer and decreasing fluidity.
39
Q

Lipid bilayer is symmetric (T/F)

A

False, it is assymetric.

40
Q

The lipid composition of two leaflets of the lipid bilayers in many membranes

A

are different.

41
Q

Lipids present in the extracellular leaflet + explain assymetry

A
  • glycolipids and sphingomyelin.
  • the asymmetry is generated by both glycolipids and sphingomyelin are produced by enzymes exposed to the Golgi lumen and are not substrates for flippases.
42
Q

Phosphatidylcholine is mostly present in which leaflet

A

extracellular leaflet.

43
Q

Glycerol phospholipids mostly present in the cytosolic leaflet + explain asymmetry.

A
  • phosphatidylethanolamine and phosphatidylserine.
  • asymmetry generated by flippases, moving these glycerol phospholipids from the extracellular leaflet t the cytosolic leaflet.
44
Q

Type of lipid that distributes equally in each bilayer leaflet

A
  • cholesterol, spontaneously shuttles (flip-flops) between the leaflets.
  • does not require flippases.
45
Q

Specific flippases recognize different substrates (T/F)

A

True.