Membrane lipids and proteins Flashcards Preview

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Flashcards in Membrane lipids and proteins Deck (65)
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1
Q

Describe the membrane?

A

Two-dimensional sea of mobile lipid in which proteins diffuse.

2
Q

At what scale do the lipids move?

A

Nano meter scale.

3
Q

What two things does the cell membrane include?

A

> Plasma membrane.

> Internal membranes (eg. ER, Golgi)

4
Q

What 3 things does the membrane contain?

A

> Lipids
Proteins
Carbohydrate (glyco-proteins, -lipids)

5
Q

Ratio between lipids and proteins depends on?

A

Function.

6
Q

What would be the ratio of lipids:proteins for a myelin?

A

Insulating membrane.

The function is for insulation. Therefore, the lipid composition ratio is higher than protein.

7
Q

What is the major responsibility for the membrane lipids?

A

Barrier propertires.

8
Q

Name the 4 types of the major membrane lipids?

A

> Phospholipid
Steroids
Neutral fats
Glycolipid

9
Q

Phospholipid:

Properties

A

Amphipathic
Polar head group charge.
Fatty acid chain vary in length with a degree of unsaturation.

10
Q

Steroids:
Examples
Porperties

A

Cholesterol and its esters.

Amphipathic but relatively large CH portion

11
Q

Amphipathic?

A

Have hydrophilic and hydrophobic portion.

12
Q

Neutral fats?

A

Glycerides- a fatty acid ester of glycerol

13
Q

Glycolipid?

A

Minor includes some antigens

eg. A, B

14
Q

What is the fatty acid chain length?

A

Varies

C12 to C22

15
Q

What does each C=C bond introduce to the phospholipids?

A

Introduces a rigid kink in the R tail.

16
Q

What does polar mean?

A

hydrophilic region

17
Q

What happens to phospholipids when in aqueous solution?

A

Forms bilayer.

Hydrophobic interactions cause tails to aggregate and exclude water from a “core”.

18
Q

How is the membrane stabilised?

A

By tail-tail and head-head interactions

19
Q

Name the 2 types of membrane proteins?

A

Integral (intrinsic)

Peripheral (exofacial/endofacial)

20
Q

Integral membrane protein?

A

One of more regions embedded in lipid bilayer.

Most are transmembrane proteins.

21
Q

Peripheral membrane protein?

A

Attached to membrane through integral membrane proteins or membrane lipids.

22
Q

How are transmembrane proteins arranged in the membrane?

When is orientation established?

A

Asymmetrically

During biosynthesis.

23
Q

Name the 3 types of how the span membrane?

A

Single span
Multiple spans
Multimeric protein complexes

24
Q

What would the single span function as?

A

Anchoring

Receptor-transducer function.

25
Q

What would the multiple spans function as?

A

May form an aqueous “pore” in the membrane.

Channels, transporters

26
Q

What would the multimeric protein complexes function as?

A

Central “pore”.

27
Q

Bacterial lactose permease?

A

The most abused protein on the planet.

Know the function of every amino acid.

28
Q

How many transmembrane domains does bacterial lactose permease have?

A

12 Transmembrane domains

29
Q

What two parts of this bacterial lactose permease allows it to function as a permease?

A

Glu325 and His322

30
Q

What are the 3 different net charges that amino acid residues in proteins have?

A

1) Neutral
2) Cationic
3) Anionic

31
Q

Describe neutral net charge?

A

Polar- depending on side groups (ie. OH or CO)

32
Q

Polar meaning?

A

The charge in the atom is not symmetrically.

Hydrophilic ( bond with water).

33
Q

Hydropathy index?

A

The atoms attraction to water.

ie. hydrophilic or hydrophobic

34
Q

What does the hydropathy index tell us about the amino acids side chain?

A

Its charge.

35
Q

What is the electrical charge distribution along a protein? and what does it depend on?

A

Varies and depends upon primary structure.

36
Q

How would you describe regions of high charge density (along a protein) as being?

A

Relatively hydrophilic

37
Q

How would you describe regions of low charge density (along a protein) as being?

A

Relatively hydropholic

38
Q

What type of plot would thou use to predict the protein structure?

A

Hydropathy plot

39
Q

Describe the hydropathy plot?

A

The more positive value, the more hydrophilic the amino acids are in that particular region.

40
Q

Name the 5 transmembrane domain regions that are likely to be rich in hydrophobic residues?

A
Ala
Val
Leu
Ile
Phe
41
Q

What anchors the regions within a protein?

A

Phospholipid tails.

42
Q

How many residues form alpha helix?

A

20-25 AA residues

43
Q

What do domains outwit membrane tend to be? and form?

A

Tend to be charged.

Form beta sheets

44
Q

Name the important functions that occasionally charged residues within transmembrane domains have to do?

A

Stabilising structures, binding substrates and charge transfer.

45
Q

Name the 2 residues that are found in domains outwith the membrane?

A

Gly and Pro

46
Q

What does polar peptide linkage form?

A

Shielded H-bonds within the helix

47
Q

Name the 4 methods used as evidence for the structure of the fluid mosaic model?

A

1) lipid area
2) X-ray and neutron diffraction
3) Transmission electron microscopy
4) Freeze-etching

48
Q

Describe how the lipid area can be used as evidence for the structure of the fluid mosaic model?

A

2 x membrane area

49
Q

Describe how the x-ray and neutron diffraction can be used as evidence for the structure of the fluid mosaic model?

A

There is a regular variation in density.

50
Q

Describe how the transmission electron microscopy can be used as evidence for the structure of the fluid mosaic model?

A

Uses electrons instead of light allows a much higher resolution.

51
Q

Describe how the freeze-etching can be used as evidence for the structure of the fluid mosaic model?

A

reveals embedded proteins in fracture faces.

Subliming a layer of ice crystals from the fractured plane to expose the natural surfaces.

52
Q

Name the 3 methods used as evidence for the dynamics of the fluid mosaic model?

A

1) Electron spin resonance
2) Phase-transition
3) Protein-tagging

53
Q

Describe how electron spin resonance can be used as evidence for the dynamics of the fluid mosaic model?

A

Use of spin-labelled phospholipids

54
Q

Describe how phase-transition can be used as evidence for the dynamics of the fluid mosaic model?

A

As the temp increase, the membrane starts to melt from a gel like structure to a fluid one. Therefore, shows that it is very dynamic.

55
Q

Describe how protein-tagging can be used as evidence for the dynamics of the fluid mosaic model?

A

Used to observe specific protein movement.

56
Q

Describe the difference between x-ray and neutron diffraction when being used as evidence for the structure of the fluid mosaic model?

A

X-ray identifies the phosphate and cholesterol.

Neutron identifies the ester and cholesterol.

57
Q

Why are some proteins immobile within the membrane?

A

They are anchored by the actin skeleton

58
Q

What is the barrier and exchange surface between the cell and the environment?

A

The cell membrane.

59
Q

Name the 3 mechanisms by which substances cross the membrane?

A

1) Diffusion
2) Osmosis (net water movement)
3) Transport (facilitative or active)

60
Q

Describe diffusion?

A

Can be through the bilayer or the use of a channel.

Region of high to low

61
Q

Describe facilitative transport?

A

Use of a protein to travel across the membrane (ie. useful to large molecules)
Use of the gradient (high to low)

62
Q

Describe primary active transport?

A

Use of a protein to go through the membrane.

Directly uses ATP as energy to transport these molecules against their gradient (low to high)

63
Q

Describe secondary active transport?

Whats its other name?

A

Symport.
Uses a protein as a means to travel across the membrane.
Allows 2 molecules to travel: one with its gradient and one against.
Uses the energy given by the molecules going with its gradient to transport the one against.

64
Q

What does it mean by solvent?

A

The bulk of liquid that the solute is dissolved in.

65
Q

How could you speed up diffusion?

A

Use facilitative transporters.