Membrane lipids and proteins Flashcards Preview

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

Describe the membrane?

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

2

At what scale do the lipids move?

Nano meter scale.

3

What two things does the cell membrane include?

> Plasma membrane.
> Internal membranes (eg. ER, Golgi)

4

What 3 things does the membrane contain?

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

5

Ratio between lipids and proteins depends on?

Function.

6

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

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

7

What is the major responsibility for the membrane lipids?

Barrier propertires.

8

Name the 4 types of the major membrane lipids?

> Phospholipid
>Steroids
>Neutral fats
>Glycolipid

9

Phospholipid:
Properties

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

10

Steroids:
Examples
Porperties

Cholesterol and its esters.
Amphipathic but relatively large CH portion

11

Amphipathic?

Have hydrophilic and hydrophobic portion.

12

Neutral fats?

Glycerides- a fatty acid ester of glycerol

13

Glycolipid?

Minor includes some antigens
eg. A, B

14

What is the fatty acid chain length?

Varies
C12 to C22

15

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

Introduces a rigid kink in the R tail.

16

What does polar mean?

hydrophilic region

17

What happens to phospholipids when in aqueous solution?

Forms bilayer.
Hydrophobic interactions cause tails to aggregate and exclude water from a "core".

18

How is the membrane stabilised?

By tail-tail and head-head interactions

19

Name the 2 types of membrane proteins?

Integral (intrinsic)
Peripheral (exofacial/endofacial)

20

Integral membrane protein?

One of more regions embedded in lipid bilayer.
Most are transmembrane proteins.

21

Peripheral membrane protein?

Attached to membrane through integral membrane proteins or membrane lipids.

22

How are transmembrane proteins arranged in the membrane?
When is orientation established?

Asymmetrically
During biosynthesis.

23

Name the 3 types of how the span membrane?

Single span
Multiple spans
Multimeric protein complexes

24

What would the single span function as?

Anchoring
Receptor-transducer function.

25

What would the multiple spans function as?

May form an aqueous "pore" in the membrane.
Channels, transporters

26

What would the multimeric protein complexes function as?

Central "pore".

27

Bacterial lactose permease?

The most abused protein on the planet.
Know the function of every amino acid.

28

How many transmembrane domains does bacterial lactose permease have?

12 Transmembrane domains

29

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

Glu325 and His322

30

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

1) Neutral
2) Cationic
3) Anionic

31

Describe neutral net charge?

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

32

Polar meaning?

The charge in the atom is not symmetrically.
Hydrophilic ( bond with water).

33

Hydropathy index?

The atoms attraction to water.
ie. hydrophilic or hydrophobic

34

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

Its charge.

35

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

Varies and depends upon primary structure.

36

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

Relatively hydrophilic

37

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

Relatively hydropholic

38

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

Hydropathy plot

39

Describe the hydropathy plot?

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

40

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

Ala
Val
Leu
Ile
Phe

41

What anchors the regions within a protein?

Phospholipid tails.

42

How many residues form alpha helix?

20-25 AA residues

43

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

Tend to be charged.
Form beta sheets

44

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

Stabilising structures, binding substrates and charge transfer.

45

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

Gly and Pro

46

What does polar peptide linkage form?

Shielded H-bonds within the helix

47

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

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

48

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

2 x membrane area

49

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

There is a regular variation in density.

50

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

Uses electrons instead of light allows a much higher resolution.

51

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

reveals embedded proteins in fracture faces.
Subliming a layer of ice crystals from the fractured plane to expose the natural surfaces.

52

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

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

53

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

Use of spin-labelled phospholipids

54

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

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

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

Used to observe specific protein movement.

56

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

X-ray identifies the phosphate and cholesterol.
Neutron identifies the ester and cholesterol.

57

Why are some proteins immobile within the membrane?

They are anchored by the actin skeleton

58

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

The cell membrane.

59

Name the 3 mechanisms by which substances cross the membrane?

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

60

Describe diffusion?

Can be through the bilayer or the use of a channel.
Region of high to low

61

Describe facilitative transport?

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

62

Describe primary active transport?

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

Describe secondary active transport?
Whats its other name?

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

What does it mean by solvent?

The bulk of liquid that the solute is dissolved in.

65

How could you speed up diffusion?

Use facilitative transporters.