Unit 3: Membranes

Question 1

Functions of biological membranes

Answer 1

1. Compartmentalization
2. Scaffolding for biochemical activities
3. Selectively permeable barrier
4. Transporting solutes
5. Responding to external signals
6. Intercellular interaction
7. Energy transduction

Question 2

Specific function of the plasma membrane

Answer 2

1. Import/export of molecules
2. Receiving information
3. Capacity for mvmnt and expansion

Question 3

What determines the function of biological membranes?

Answer 3

The proteins embedded!

Question 4

Cell membranes composed of

Answer 4

Lipids and proteins

Question 5

Lipid bilayer is approximately ____ thick

Answer 5

~ 5nm

Question 6

Each row of lipids called a

Answer 6

Leaflet

Question 7

When talking about organelles within a cell, the outer faces the _____ and the inner faces the _____

Answer 7

Cytosol,
Lumen.

Question 8

The plasma membrane outer leaflet is facing ______ and the inner leaflet is facing _____

Answer 8

Outside cell,
Inside cell (cytosol)

Question 9

Inner of golgi faces the ______, outer of golgi faces _____

Answer 9

Lumen,
cytosol

Question 10

____ portion of leaflets face eachother

Answer 10

Hydrophobic

Question 11

Molecules with hydro(philic and phobic portions) called

Answer 11

Amphipathic

Question 12

Proteins that can cross membrane

Answer 12

Must be longer than 5nm and hydrophobic

Question 13

Fatty acid composed of

Answer 13

Carboxyl group makes it acidic
Long hydrocarbon chain (saturated or unsaturated)

Question 14

____ fatty acids can pack more tightly, whereas _______ fatty acids with kinks creates more space and hence fluidity.

Answer 14

Saturated,
Unsaturated

Question 15

Three main types of membrane lipids (most to least abundant)

Answer 15

1. Phosphoglycerides
2. Sphingolipids
3. Cholesterol

Question 16

Phosphoglycerides

Answer 16

Are diacylglycerides with small functional head groups linked to the glycerol backbone by phosphate ester bonds.

Question 17

Sphingolipids

Answer 17

are ceramides formed by the attachment of sphingosine to fatty acids.

Question 18

Most abundant phosphoglyceride

Answer 18

Phosphotidylcholine: choline + phosphate + glycerol+ 2x Fatty acid tails.

Question 19

Most abundant phospholipid in most cell membranes is:

Answer 19

Phosphatidylcholine

Question 20

Least abundant phospholipid

Answer 20

Phosphatidylinositol: important for cellular signaling because of ability to cleave between glycerol and phosphate. Releases phosphoinositol

Question 21

Release of phosphoinositol pathway

Answer 21

IP3 due to phosphorylation (regulating proteins)

Question 22

Sphingolipids (chain of command)

Answer 22

1. Sphingosine
2. Add second fatty acid to sphingosine via amine group ~ Ceramide
3. Add phosphorylcholine to ceramide ~ Sphingomyelin
4. Add galactose to ceramide ~ cerebroside
5. Add complex carbohydrate to ceramide ~ ganglioside

Question 23

Sphingolipids abundant in

Answer 23

Nervous tissue

Question 24

Sugar substituted lipids known as

Answer 24

Glycolipids

Question 25

All cell membranes (aside from phosphoglycerides, sphingolipids and glycolipids) contain

Answer 25

Cholesterol

Question 26

Cholesterol is

Answer 26

Amphipathic

Question 27

What dictates hydrophilic behaviour in bilayer?

Answer 27

Hydrophilic molecules in water behave by dissolving due to polar charges and form H-bonds with water molecules (it is more energy favourable state)

Question 28

Hydrophobics behaviour in bilayers:

Answer 28

Can’t form bonds with water molecules. Water makes a cage-like structure around it. This disturbs energy favourable state with non-energy favourable state because H-bond is disripted.

Question 29

Why membranes form a bilayer?

Answer 29

Cage structure or water molecules around the hydrophobic requires energy. System wants to be in lowest energy state.

Energy cost minimized if hydrophobic molecules cluster together

Question 30

When hydrophobics cluster together, two things can happen… what happens depends on this:

Answer 30

1. Micelle
2. Lipid bilayer

Depends on the shape of the fatty acid tail.

Question 31

Ends of bilayers result in

Answer 31

Self-sealing properties: exposed edges rearrange spontaneously to be energetically more favourable state not exposed to water.

Question 32

Why do microsomes and vesicles (made of plasma membrane) form a ball and not a sheet?

Answer 32

Because edges of sheet are hydrophobic, exposed to water. For most energy favourable state, those lipids will spont. form a sphere and fold so edges associate one another (inside sphere is liquid).

Question 33

Pure phospholipids in water will spontenously form

Answer 33

Liposomes

Question 34

Lipid bilayer behaves as 2D fluid, why is this necessary?

Answer 34

For many proteins, for them to do their function they need to move around a bit. They need that environment to be a bit fluid-like.

Question 35

Three types of lipid mobility account for fluidity:

Answer 35

1. Lateral diffusion
2. Rotation
3. Flip-flop

Question 36

Lipid movement 1: Lateral diffusion

Answer 36

Lipids rapidly exchange places with their neighbors on same leaflet

Question 37

Lipid movement 2: Rotation

Answer 37

Rotate on own axis. Kinks in unsaturateds help do this

Question 38

Lipid movement 3: Flip-flop

Answer 38

From one leaflet to the other, by route of flippases (enzyme) to move it.

Cholesterol can flip rapidly on its own.

Question 39

How did they determine fluid nature of membranes?

Answer 39

Using FRAP: Fluorescence Recovers After Photobleaching

laser beam bleaches area with fluorescent dye. then dye fills it in eventually by diffusing in.

Question 40

Why don’t bilayers fuse spontaneously to the closest…

Answer 40

Because the cage-structure (hydration shell) of the polar head acts as insulator and isn’t easily displaced. Membrane fusion requires energy.

Question 41

Two main properties of lipids contribute to fluidity

Answer 41

1. Length of hydrocarbon tail
2. Degree of saturation.

Question 42

Shorter tail length ~

Answer 42

increases fluidity because of less hydrophobic interactions.

Question 43

Cholesterol makes bilayer less fluid at _____, but keeps it fluid at

Answer 43

High temperature,
Low temperature

Question 44

Unless acted on by flippases, the orientation of lipids on leaflet is the same.

Question 45

_____ and _____ are only in the outside (extracellular) leaflet

Answer 45

Glycololipids,
Sphingomyelin

Question 46

Cytosol cannot have specificity for

Answer 46

sphingomyelin and glycolipids

Question 47

Ceramide is the precursor for

Answer 47

Sphingomyelin and glycolipids

Question 48

Ceramide sitting on the ______ and can thus be converted to sphingomyelin

Answer 48

lumenal leaflet

Question 49

Phosphatidylcholine is mostly found in the

Answer 49

Outer leaflet

Question 50

Asymmetry of phospholipids is due to

Answer 50

flippases

Question 51

Phosphatidylinositol found mostly on

Answer 51

Cytosolic side (inner leaflet)

Question 52

Phospholipids synthesized in the

Answer 52

Smooth ER.

Question 53

Membrane orientation does not change during transfer between compartments, thus:

Answer 53

Lipids facing the cytosol remain cytosolic even at the plasma membrane. Those facing the lumen of a compartment will face the extracellular space.