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Cellular Composition > Membrane Transport and Structure > Flashcards

Membrane Transport and Structure Flashcards

1
Q

Give 4 realistic features of the fluid mosaic model

A
  • Crowded bilayer
  • Patchwork appearance
  • Local bilayer distortion
  • Protein complexes
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2
Q

Why do lipids spontaneously self-associate?

A

The hydrophobic effect and van der Waals interactions between the fatty acid tails

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3
Q

What is one of the main components of many membranes?

A

Glycerophospholipids

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4
Q

Why is cholesterol important in membranes?

A

Modulates packing of lipids and fluidity of membrane

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5
Q

Give the 4 ways lipids can move in a membrane

A
  • flip-flop from one side of membrane to the other
  • lipids diffuse laterally (movement left or right in the same leaflet)
  • rotate freely around their long axis
  • hydrocarbon chains are flexible and dynamic so wobble
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6
Q

What is the transition temperature of a membrane?

A

The temperature at which bilayers change from a fluid to a rigid gel phase

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7
Q

What is the effect of shorter chains or double bonds in phospholipids on transition temperature?

A

It lowers it

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8
Q

How is lateral diffusion affected by membranes being in the gel phase?

A

It is greatly reduced

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9
Q

Name the 2 enzymes involved in the maintenance of membrane asymmetry

A

Flippase and floppase

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10
Q

Give an example of a lipid transported by flippase

A

Phosphatidylserine

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11
Q

What do flippase and floppase use as a source of energy?

A

ATP hydrolysis

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12
Q

Which direction does floppase move lipids?

A

From the inner to the outer leaflet (against conc. gradient)

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13
Q

Which direction does flippase move membrane lipids?

A

From outer to inner leaflet (against conc. gradient)

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14
Q

Give an example of a lipid moved by floppase

A

Sphingolipid

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15
Q
A
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16
Q

Are integral membrane proteins generally soluble in aqueous buffers?

A

No

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17
Q

What is the only way integral membrane proteins can be separated from membranes?

A

By using agents which disrupt membranes

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18
Q

Are peripheral membrane proteins often soluble in aqueous buffers?

A

Yes

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19
Q

How are peripheral membrane proteins bound?

A

To the surface only via binding to integral membrane proteins and/or directly with the lipid headgroup regions

20
Q

What is the typical structure of integral membrane proteins?

A
  • α-helical or ß-barrel
  • Structured or unstructured loops outside the membrane
21
Q

Which is the more common structure for integral membrane proteins?

A

α-helical

22
Q

Where are ß-barrel integral membrane proteins found?

A

In bacterial outermembranes, mitochondria, and chloroplasts

23
Q

What type of amino acids do integral membrane proteins contain a lot of?

A

Hydrophobic

24
Q

What is the typical length of an α-helix?

A

20-25 amino acids

25
Q

How can α-helices be predicted?

A

The prescence of a string of hydrophobic amino acids in the sequence

26
Q

What types of amino acids are found in ß sheets?

A

Alternating polar and hydrophobic amino acids

27
Q

Are all membranes asymmetric?

A

No but many are

28
Q

What is the difference between a transporter and a channel?

A

A transporter transports molecules down/against a concentration gradient whereas a channel only allows for diffusion down a concentration gradient

29
Q

What is the effect of increasing concentration of the transported molecule on rate of transport in channel proteins?

A

It increases proportionally to the increase in concentration

30
Q

What is the effect of increasing concentration of the transported molecule on rate of transport in transporters?

A

It increases but plateaus off (follows Michaelis-Mensen kinetics)

31
Q

Where do solute transporters get their energy to transport molecules against a concentration gradient from?

A

The movement of one solute from [high] to [low] aka cotransport

32
Q

What are the 3 types of transporter?

A
  • Uniport
  • Symport
  • Antiport
33
Q

Describe the movement of a symport transporter

A
34
Q

Describe the direction of an antiport transporter

A
35
Q

The hydrolysis of 1ATP moves what in ATPase?

A
  • 3Na+
  • 2K+
36
Q

How many Na+ are moved out of a cell for every 2k+ moved in?

A

3

37
Q

How many K+ are moved in for every 3 Na+ moved out?

A

2

38
Q

Briefly outline the structure of ATPase

A

The region of binding and hydrolysis of ATP is distinct from the region through which ions travel

39
Q

What does the F in the Nerst equation represent?

A

The Faraday constant

40
Q

Give an example of sodium transporters in health and disease

A
  • Glucose uptake depends on Na+:glucose symporters
  • These transporters promote te readsorption of glucose from the bloodstream
  • Inhibitors of SGLTs can be used to treat diabetes
41
Q

Give an example of a proton-coupled transporter

A

Lactose Permease

42
Q

Why type of transporter is lactose permease?

Outline the movement of the molecules

A

Symport (H+ are moved from high to low conc. whilst lactose is moved from low to high)

43
Q

What is the mechanism for LacY? (lactose permease)

A
  • Never fully opens a pore (Sealed by a rocker-switch mechanism)
  • Position of an H bond moves in order to allow for a conformational change in shape
44
Q

Give the features of ABC transporters

A
  • Use ATP binding and hydrolysis to directly power transport
  • Both export and import substances
45
Q

Give an example of ABC transporters in context of health and disease

A
  • MDR1 is a transporter whose natural function is to protect cells from toxic compounds
  • It is a problem as it pumps drugs out of a cell
  • Involved in aquired multidrug resistance in cancer
46
Q

How does light-activated transport work?

A
  • Bacteriorhodopsin absorbs light at a certain wavelength
  • Upon light activation, it moved H+ across the membrane and generates a proton motive force

Cellular Composition (15 decks)

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