Biological Membranes Flashcards

1
Q

What are lipids

A

Compounds which are primarily: Non-polar, Amphipathic, Hydrophobic, Insoluble in water

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2
Q

What do lipids include

A

Fatty acids, Triacylglycerols (Typically contain fatty acids), Membrane Lipids (Typically contain fatty acids) and Cholesterol

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3
Q

What are fatty acids

A

Long chain hydrocarbon carboxylic acids. Up to 24 carbons long (16 and 18 most common). General formula CH3(CH2)nCOO(-) Amphipathic (Amphiphilic) Polar and non-polar portions

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4
Q

What are saturated fatty acids

A

No double bonds

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5
Q

What are unsaturated fatty acids

A

Double bonds, mono- or polyunsaturated (one or more double bonds).

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6
Q

How does length affect fatty acids

A

Longer fatty acids melt at higher temperatures. Shorter fatty acids melt at lower temperatures.

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7
Q

How does saturation affect fatty acids

A

Saturated fatty acids melt at higher temperatures. Unsaturated fatty acids melt at lower temperatures. Saturation has a greater effect on melting point than length.

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8
Q

What is the difference between fatty acids packing together

A

Saturated can align closely, maximising Van der Waal’s interactions between them. In contrast, the fatty acids that have both saturated and unsaturated fatty acids. These molecules cannot pack as closely together because of the bend in the unsaturated hydrocarbon chain. Trans fatty acids do not adopt the same shape as cis one and are able to pack better.

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9
Q

What are Triacylglycerol (TAG)

A

Triacylglycerol (TAG) is a way of storing fatty acids. TAG is very hydrophobic (not amphipathic) Triacylglycerol: Three acyl chains are attached to glycerol. Acyl chains from fatty acids (ester-linked)

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10
Q

What are the possible makeups of a membrane lipids

A

Glycerophospholipids, Sphingolipids and Cholesterol

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11
Q

What are glycerophospholipids made up of

A

Like triacylglycerol, glycerol has fatty acyl groups covalently attached. Unlike triacylglycerol, the presence of a large polar group makes these molecules amphipathic. Variations exist in polar head groups and acyl chains, affecting size and melting points.

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12
Q

What are cholesterols made up of

A

Accounts for ~35% of mammalian membranes. Rigid, non-polar structure (hydrocarbon/ring structure). Weakly amphipathic (single -OH; weakly polar on the -OH side and very hydrophobic everywhere else). Most hydrophobic (27 carbons, 1 OH; very weakly amphipathic). Membrane lipid ~30% of mammalian plasma membranes. Maintains fluidity and rigidity. Does not form membranes alone. The -OH associates with polar head groups of other lipids. Non-polar portion is found in the membrane.

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13
Q

What happens when amphipathic molecules form Micelles or Bilayers in Water

A

These arrangements eliminate unfavourable contact between H2O and hydrophobic tails, yet permit solvation of polar head groups.

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14
Q

What do liposomes form

A

An inner and an outer leaflet which make a bilayer

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15
Q

What are bilayers formed of

A

Vary depending on lipid composition: Acyl chain and Polar head group. Non-covalent assembly: Fluid yet stable.

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16
Q

How are the dimensions of lipid bilayers variable

A

The lipid head groups have significantly different dimensions. The acyl trails vary between 16-20 carbon atoms in length. Cholesterol is almost entirely buried in the bilayer. Despite their fluidity, lipid bilayers are stable.

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17
Q

What happens when the lipid bilayer is below the transition temperature

A

Below the transition temperature, acyl chains pack together in Van der Waals contact, in a gel-like solid state.

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18
Q

What happens when the lipid bilayer is above the transition temperature

A

Above the transition temperature, the lipid molecules and their acyl chains move freely and rapidly.

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19
Q

What happens when the lipid bilayer is at the transition temperature

A

The melting temperature (transition temperature) of a lipid bilayer is the temperature of its transition from an ordered crystalline to a more fluid state and depends on acyl-chain unsaturation and length. Transition temperature may be very sharp for an artificial membrane. Homogenous preparation. However, for biological membranes the transition temperature is typically not sharp. Mixture of compounds (different lipids/proteins). Membranes must operate above gel temperature (melting point) but not be completely disordered.

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20
Q

How do they maintain membrane fluidity

A

Adapting to differences in temperature will affect the lipid composition of a biological membrane. With decreasing temperature, more unsaturated fatty acids and shorter fatty acids are incorporated into membrane lipids. With increasing temperature, more saturated fatty acid and longer fatty acids are incorporated into membrane lipids.

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21
Q

How does cholesterol impact membrane rigidity

A

In animals. Because it is rigid and planar, cholesterol limits the rotational movement of neighbouring acyl tails, thereby increasing Van der Waals interactions. Cholesterol increases membrane fluidity for a larger effective temperature range. Low temperature: prevents close packing between acyl chains. High temperature: decreases motion/disorder of acyl chains, increases rigidity. Cholesterol is not found in bacteria.

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22
Q

How can lipids move freely through the bilayer

A

Lipids move freely and rapidly in the bilayer, but only laterally.

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23
Q

How can it be difficult lipids to move through the bilayer

A

Lipids do NOT undergo transverse (flip-flop) at appreciable rates.

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24
Q

How do lipids flip from one side of the lipid bilayer to the other

A

“Flipases” (and other enzymes) increase the rate of transverse diffusion. Specific transport by these proteins allows for differences in lipid composition in the leaflets. A significant energy barrier is associated with desolvating a polar head group to move it through a hydrophobic bilayer.

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25
Q

What are the types of Membrane Proteins

A

Integral membrane protein, peripheral membrane protein and lipid-linked protein

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26
Q

Describe integral membrane proteins

A

Hydrophobic interactions. Polar surface on the outside of the membrane and hydrophobic surface on the inside on the membrane

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27
Q

Describe peripheral membrane protein

A

Polar/Ionic/Electrostatic interactions, on the outside of the membrane. Can be disrupted via changing the concentrations of the environment like salts.

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28
Q

Describe lipid-linked proteins

A

Lipid prosthetic group inside the membrane that is hydrophobic, tightly associated with the bilayer but less so than the integral membrane protein. Hydrophobic interactions via prosthetic group.

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29
Q

Where is the contact points of the integral membrane proteins

A

The portion of an integral membrane protein that is in contact with the acyl tails of the bilayer must have hydrophobic amino acid side chains on its surface. Interactions with water occurs with the polar surface.

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30
Q

What side chains are the K+ Channel

A

Nonpolar side chains make up most of the helix surfaces that face the lipid tails. Polar side chains are more prominent in the loops, interacting with the lipid head groups and solvent. Very polar side chains (Asp, Glu, Lys, and Arg) often flank these regions, interacting with solvent.

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31
Q

What role do regular secondary structures cross membran

A

Regular structures satisfy the hydrogen bond potential of the polypeptide backbone

32
Q

Do amino acids form a transmembrane alpha-helix that is generally hydrophobic

A

True

33
Q

What is the Fluid Mosaic Model of Membrane Structure

A

Dynamic, non-covalent, complex assembly of lipids and proteins (and carbohydrates). Both lipids and proteins move laterally but cannot (easily) undergo transverse movement. The movement of proteins may be limited by the cytoskeleton. Carbohydrate chains are attached to the extracellular surface of some proteins and lipids.

34
Q

How do gases and hydrophobic molecules pass through the bilayer

A

Gases and Hydrophobic molecules pass freely across the bilayer

35
Q

How do small polar molecules pass through the bilayer

A

Small polar molecules often need assistance to pass through the bilayer but they have an easier time passing through than polar and charged molecules

36
Q

How do large polar and charged molecules pass through the bilayer

A

Large polar molecules and charged molecules must have assistance because they won’t traverse the membrane wit some kind of assistance

37
Q

What does the rate of simple unmediated diffusion depend on?

A

Size of molecule, concentration gradient and lipid solubility

38
Q

How does the size of molecule affect diffusion

A

Smaller molecules move faster than larger ones

39
Q

How does the concentration gradient affect diffusion

A

Larger gradient increase rate of diffusion. Smaller gradient decreases rate of diffusion

40
Q

How does the lipid solubility affect diffusion

A

Largest impact of the other factors. Greater solubility increases diffusion rate. Less solubility decreases diffusion rate.

41
Q

What direction does simple diffusion go in

A

Simple diffusion is always down the concentration gradient

42
Q

What are the two MAJOR types of transport

A

Passive and active

43
Q

What happens when Delta G is negative

A

The motion is spontaneous, passive transport

44
Q

What happens when Delta G is positive

A

Energy must be provided to make transport occur, active transport

45
Q

What are porins

A

Porins contain a relative non-specific, water-filled pore in the center of a beta-barrel. Most porins are trimers (3 subunits). Each subunit contains a pore. Non-selective – free diffusion up to 1.5K Daltons

46
Q

What are ion channels

A

The channel is formed between subunits. They are highly selectrive

47
Q

What occurs in a K+ ion channel

A

Selectivity depends on the size of the pore and the properties of the side chains/functional groups found there. Potassium ions interacts with the carbonyl subunit groups surrounding.

48
Q

What happens when Sodium ions go through a K+ channel

A

Sodium ions are smaller but cannot interact with all the carbonyl subunits simultaneously, so this results in a slow transport through this channel.

49
Q

What is the conformational change transport

A

Transporter (carrier) proteins. Do not have membrane-spanning pores. Conformational change alternates openings from one side of the membrane to other. Selective for substrate transported. May be passive or active.

50
Q

What is the graph for passive transport by carrier proteins

A

It is hyperbolic

51
Q

What is a uniport

A

One molecule can be transported in one direction

52
Q

What is a symport

A

Many molecules can be transported in one direction

53
Q

What is an antiport

A

Many molecules can be transported in two directions

54
Q

What is the energy source for primary active transporters

A

Primary active transporters typically uses ATP as the source of free energy

55
Q

What is the energy source for secondary active transporters

A

Secondary active transporters uses an ion gradient (Na+) as the source of free energy

56
Q

Is there a transport protein in simple diffusion

A

No

57
Q

Is there a transport protein in channels and pores

A

Yes

58
Q

Is there a transport protein in passive transport

A

Yes

59
Q

Is there a transport protein in primary active transport

A

Yes

60
Q

Is there a transport protein in secondary active transport

A

Yes

61
Q

Is simple diffusion saturable with substrate

A

No

62
Q

Are channels and pores saturable with substrate

A

No

63
Q

Is passive transports saturable with substrate

A

Yes

64
Q

Is primary active transport saturable with substrate

A

Yes

65
Q

Is secondary active transport saturable with substrate

A

Yes

66
Q

What is the movement relative to concentration gradient in simple diffusion

A

Down

67
Q

What is the movement relative to concentration gradient in channels and pores

A

Down

68
Q

What is the movement relative to concentration gradient in passive transport

A

Down

69
Q

What is the movement relative to concentration gradient in primary active transport

A

Up

70
Q

What is the movement relative to concentration gradient in secondary active transport

A

Up

71
Q

Is there energy input required for simple diffusion

A

No

72
Q

Is there energy input required for channels and pores

A

No

73
Q

Is there energy input required for passive transport

A

No

74
Q

Is there energy input required for primary active transport

A

Yes, from a direct source

75
Q

Is there energy input required for secondary active transport

A

Yes, from the ion gradient

76
Q

How is Na + and K + ATPase a primary active transporter

A

In each cycle: 3 Na + ions exported and 2 K+ ions imported. ATP + H2O = ADP + Pi + H(+). The two concentration gradients generated across the cell membrane are used as the source of energy for a variety of secondary active transport processes.

77
Q

How is the Na + Glucose Transporter a secondary active transporter

A

Glucose is higher in the cytosol. Sodium is higher in the exterior. Even though glucose is a neutral compound it still requires positive energy to move across the concentration gradient. The net of the sodium glucose transport must be less than 0 for glucose import.