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IMS topic 4 - Lipids > Lipids & membranes > Flashcards

Lipids & membranes Flashcards

1
Q

Give three roles of membranes

A

Form the boundaries around the cell and its sub compartments
Act as selectively permeable barriers
Contain receptors
Generate chemical and electrical signals
Are the surfaces on which metabolic reactions can occur

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2
Q

Give the three major types of membrane lipids

A

glycerophospholipids, sphingolipids, sterols (typified by cholesterol)

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3
Q

What are glycerolphospholipids derived from?

A

Glycerol-3-phosphate

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4
Q

What is the basic structure of a glycerolphospholipid?

A

AA 3 carbon backbone, two fatty acid groups attached to carbons one and 2 by ester bonds, a phosphate group with a specific head group on carbon 3

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5
Q

What causes the kink in a fatty acid?

A

A double bond in the hydrocarbon chain

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6
Q

What are the key components of a sphingolipid?

A

Have a sphingosine molecule as their backbone (not a glycerol like phospholipids), a fatty acid chain and a choline head group.

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7
Q

What are gangliosides?

A

A family of membrane sphingolipids that are particularly abundant in the brain

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8
Q

What does cholesterol consist of?

A

A fused ring structure with an aliphatic chain (which folds up to form a rigid, compact structure)

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9
Q

Define amphipathic

A

Lipids both have a hydrophobic part and a hydrophilic part

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10
Q

What makes lipids form a bilayer? What is this effect called?

A

It is entirely spontaneous, driven by the desire to get the hydrophobic parts as far away from the surrounding water as possible
This is called the hydrophobic effect

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11
Q

Name 3 forces that maintain the lipid bilayer structure

A

hydrophobic interactions, van der waals forces between hydrocarbon tails, charged bonds, H bonds between polar head groups and water

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12
Q

Who discovered the fluid mosaic model?

A

Singer and Nicholson 1972

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13
Q

How can lipids move in the bilayer?

A

Rotate on their axes or move laterally along the side of the membrane

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14
Q

What is each surface of the bilayer known as?

A

The leaflet

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15
Q

What are lipid rafts?

A

Parts of the membrane where some lipids and proteins cluster; have special functions

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16
Q

Do vesicles have the same structure as a lipid bilayer?

A

yes

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17
Q

Why does the membrane have fluidity?

A

There are no covalent bonds between lipids. They can rotate on their axis or move laterally sideways

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18
Q

Why do lipids not readily flip from one side of the bilayer to the other?

A

It is energetically unfavourable - the hydrophilic head group would have to be moved across the hydrophobic interior

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19
Q

What is the name of the process of lipids flipping from one side of the membrane to the other?

A

Transverse diffusion

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20
Q

How do lipids get put on the correct leaflet when it is assembled?

A

Enzymes

21
Q

Give 3 factors that influence the fluidity of the membrane and explain why

A

Heat - more energy means they will move faster
Increasing length of fatty acid chains - decrease in fluidity because there will be more hydrophobic interactions between chains
Increasing the number of unsaturated double bonds - increases fluidity because these double bonds are in the cis formation, causing a kink which disrupts the neat packing
More cholesterol - less fluidity because it adds stability

22
Q

Why is the membrane semi-fluid at room temp?

A

A combination of saturated and unsaturated lipids

23
Q

Why does frostbite occur?

A

Membrane solidifies at cold temperatures - frostbite occurs when oxygen can no longer diffuse through solidified membranes. The coldest, outermost cells die.

24
Q

Why do reindeer not get frostbite?

A

They have a different chemical structure with a high percentage of unsaturated lipids so the membranes stay fluid at low temps and oxygen can diffuse through for cell metabolism.

25
Q

What is the role of translocase enzymes?

A

They can flip phospholipids across the membrane in an energy dependent fashion (both on the plasma and internal membranes)

26
Q

What is the role of scamblase enzymes?

A

They randomise the normal membrane distribution of head groups and undo the work of translocates, to allow aminophospholipids (phospholipid with an amine group) to get from the inner side of the membrane to the outside. Only switched on under special circumstances e.g. when a platelet is activated, during apoptosis, when a sperm fertilises an egg.

27
Q

Is there a different type of scramblase enzyme for each type of lipid?

A

yes

28
Q

What is exposed when scrambles are switched on by platelet activation to lead to blood coagulation?

A

Phosphatidylserine

29
Q

Why are scramblases switched on to expose phsophatidylserine?

A

Switched on by platelet activation to allow interaction with blood clotting factors on the platelets and trigger blood coagulation

30
Q

What are the three stages of apoptosis?

A

Apoptotic cell releases ‘find me’ signals to attract phagocytes
The cell exposes ‘eat me’ signals included phsphatidyl serine
The apoptotic cell is engulfed and digested by the phagocyte

31
Q

Give two reasons cells trigger apoptosis

A

If they are infected by a virus or are in the way of other cell devlopment

32
Q

What is the role of deasturase enzymes?

A

They are capable of introducing double bonds into fatty acids. Fatty acids must be esterified to carrier molecule coenzyme A while this change is carried out, but are released afterwards

33
Q

What is the main role of lipid rafts?

A

Signalling platforms for cellular processes

34
Q

Why are rafts often rich in cholesterol and sphingolipids

A

Sphingolipids can pack closely with cholesterol

35
Q

How can lipid rafts be isolated in the lab?

A

centrifugation

36
Q

Name two diseases linked to neuronal lipid raft alterations

A

Huntington’s
Alzheimers
Niemman-Pick type C

37
Q

Name a disease linked to autoimmune raft alterations

A

Lupus

Rheumatoid Arthritis

38
Q

What types of lipid rafts form in endocytosis?

A

Caveolae and invaginate

39
Q

What are lipid rafts in endocytosis?

A

Anchoring points for anything that wants to enter the cell

40
Q

What is a caveolae?

A

A structure of polymerised lipids that surround a virus or other molecule that enters the cell by endocytosis

41
Q

Give an example of a glycolipid

A

Ganglioside

42
Q

What is the main feature of a glycolipid? What is the role of this?

A

Very hydrophilic sugar groups exposed on the outer face of the plasma membrane that act as receptors

43
Q

Where in production are the sugars added to gangliosides?

A

In the ER an Golgi

44
Q

How are glycolipids adapted in the cell?

A

Re-internalised during endocytosis and the vesicles fuse with lysosomes to trim the sugar back

45
Q

Glycolipids are an essential recognition site in which system?

A

ABO blood identification type

Immune system

46
Q

What does the binding of red blood cells to glycolipids initiate?

A

Agglutination (clumping of RBCs)

47
Q

Define ampipathic

A

both hydrophilic and hydrophobic

48
Q

What are liposomes? Can they be found naturally?

A

Simple, flexible vesicles that can be produced artificially and loaded with dyes, drugs, DNA, RNA for targeted drug delivery or diagnostic use

Found naturally in the blood originating from remains of cells

IMS topic 4 - Lipids (6 decks)

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