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Medicine Year 1 Semester 1 - Part 2 > Lipids in Cell Membranes > Flashcards

Lipids in Cell Membranes Flashcards

1
Q

What is a lipid ?

A

Have low solubility in water

  • Phospholipids
  • Fats
  • Sterols e.g. cholesterol
  • (Some) Vitamins
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2
Q

What do lipids do ?

A

Sources of energy
Form membranes
Participate in cell signalling

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3
Q

Function of fatty acids

A

Principal store of energy

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4
Q

Where are fatty acids found ?

A

Rarely free in the body, found more frequently in :

  1. Part of a lipid molecule
  2. Complexed to a carrier protein e.g. human serum albumin
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5
Q

Which fatty acids can be absorbed into the bloodstream ?

A

Short and medium chain fatty acids

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6
Q

Which fatty acids cannot be absorbed into the bloodstream ?

A

Long chain fatty acids
So, they are synthesised

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7
Q

Why are trans fats difficult to break down ?

A

They have one or more double bonds which are stronger and more difficult for the body to break down.

They are UNsaturated fatty acids

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8
Q

Ratio of single to double bonds in saturated fatty acids

A

16:0

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9
Q

Ratio of single to double bonds in unsaturated fatty acids

A

18:1

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10
Q

Ratio of single to double bonds in polyunsaturated fatty acids

A

20:4

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11
Q

How are double bonds numbered in fatty acids ?

A

Delta

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12
Q

Describe a feature of polyunsaturated fatty acids

A

The double bonds are never conjugated and are separated.

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13
Q

Stearic acid

A

Saturated

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14
Q

Oelic acid

A

Unsaturated - cis

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15
Q

Eladic acid

A

Unsaturated - trans

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16
Q

Omega fatty acids

A

Unsaturated

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17
Q

Sterols

A

Bile acids
Steroid hormones
Vitamins
Cell membranes - e.g. cholesterol

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18
Q

Name some inherited disorders in lipid pathways

A

Gaucher’s
Neimann Pick
Tay-Sachs
Fabry disease

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19
Q

Describe inherited disorders in lipid pathways

A

Defects in enzymes which metabolise lipids leading to lipid accumulation.

Largely affect neurological system, liver, spleen and bone marrow.

Failure to thrive.

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20
Q

Name some membrane lipids

A

Phospholipids
Glycolipids
Sterols

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21
Q

Name the types of phospholipids

A

Glycerophospholipids
- Choline
- Ethanolamine
- Serine
- Inositol

Sphingolipids

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22
Q

Name a glycolipid

A

Sphingolipids

23
Q

Name a sterol

A

Cholesterol

24
Q

Describe a phospholipid

A

Polar head group
Phosphate
Glycerol backbone
Fatty acid chains

25
Q

Describe a feature of glycolipids

A

They have a sphingosine core

26
Q

Describe the phospholipid bilayer

A

Hydrophilic heads - face the water - energetically favourable

Hydrophobic tails - are shielded from the water and lie next to each other

CONFLICTING FORCES

27
Q

Why are membranes important ?

A

Compartmentalisation

Organelles as well as plasma membrane

Highly selective barriers

Have sensors to respond to internal and external conditions.

28
Q

Name the 2 classes of proteins

A

Intergal proteins - (intrinsic)
Peripheral proteins - (extrinsic)

29
Q

Describe the movement of lipids and proteins ?

A

Rotational and lateral movement

30
Q

Briefly describe membrane fluidity with unsaturated hydrocarbon tails

A

FLUID
Lipids containing unsaturated fatty acids increase membrane fluidity.

The presence of double bonds introduces kinks in the fatty acid chains, making them more difficult to pack together.

31
Q

Briefly describe membrane fluidity with saturated hydrocarbon tails

A

VISCOUS
In their saturated form, the fatty acids in phospholipid tails are saturated with bound hydrogen atoms; there are no double bonds between adjacent carbon atoms.

This results in tails that are relatively straight.

Thus, if saturated fatty acids, with their straight tails, are compressed by decreasing temperatures, they press in on each other, making a DENSE AND FAIRLY RIGID membrane.

32
Q

What determines the fluidity in the membrane at cold temperatures ?

A

The ratio of saturated and unsaturated fatty acids determines the fluidity in the membrane at cold temperatures.

33
Q

FRAP

A

Fluorescence recovery after photobleaching

34
Q

What is FRAP ?

A

A standard technique used to study the diffusion properties of biomolecules in artificial or cell membranes.

35
Q

Why is composition of cell membrane important ?

A

Important for cell function.
Not all membranes have the same composition.

36
Q

Where is sphingomyelin mainly found ?

A

Outer leaflet

37
Q

Where is phosphatidylcholine mainly found ?

A

Outer leaflet

38
Q

Where is phosphatidylethanolamine mainly found ?

A

Inner leaflet

39
Q

Where is phosphatidylserine mainly found ?

A

Inner leaflet only

40
Q

How is asymmetry generated ?

A

New phospholipid is synthesised by enzymes at the ER facing the cytosol.

They use fatty acids available in the cytosol.

They release new phospholipid into the outer leaflet of the ER bilayer.

Lipids are then transferred to other side by flippases.

Some flippases are selective for particular phospholipids so different types may be concentrated in each monolayer.

41
Q

Flippase mechanisms

A

Pore model
“Slip-pop” model

42
Q

Describe membrane synthesis

A

Membrane synthesis occurs in the ER.

New membrane is then transported to other parts of the cell.

Occurs through a series of vesicle budding and fusion.

Bits of membrane pinch off from ER to form vesicles and then fuse with other membranes (this is called vesicle trafficking).

43
Q

Exocytosis

A

Delivery of lipids (and membrane proteins!) to cell membrane.

Allows movement of other molecules out of cell.

44
Q

Endocytosis

A

Movement of materials into cells via membrane bound vesicles.

Especially important in immune response.

May be mediated by specific receptors.

45
Q

Describe lipid rafts

A

Organising centre :

  • Vesicle trafficking
  • Cell signalling
46
Q

Function of membrane proteins

A

Many molecules cannot diffuse across a lipid membrane.

Require specific transport (active/passive)

Transmembrane signalling.

47
Q

Name the 4 types of membrane proteins

A
  1. Transmembrane
  2. Membrane associated
  3. Lipid-linked
  4. Protein-attached
48
Q

What are transmembrane proteins ?

A

Alpha helixes

49
Q

What can proteins do through membranes ?

A

They can create channels and pores through membranes.

50
Q

Membrane associated proteins

A

Usually contain domains that selectively bind to phospholipids.

Compartment-specific association

For example, pleckstrin homology domains (PH)

~100 amino acid region found in many proteins that binds to certain types of phospholipid

51
Q

What does removal of the PH domain do ?

A

It alters a protein’s membrane binding properties.
e.g. Phospholipase C-n2

52
Q

GPI

A

Glycosylphosphatidylinositol

53
Q

How are lipid-linked proteins linked ?

A

Through GPI-anchors

54
Q

Protein-attached proteins

A

Especially important in signal transduction

Beta2 adrenergic receptor
Plasma membrane
G protein signalling complex

Medicine Year 1 Semester 1 - Part 2 (37 decks)

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