Membranes + Transport (ch 10, 11)

Question 1

In what 4 ways can lipids move in the membrane bilayer?

Answer 1

1. Lateral diffusion
2. Flexion
3. Rotation
4. Flip-flop (rare)

Question 2

What are the 2 types of phospholipids?

Answer 2

1. Phosphoglycerides

2. Sphingolipids

Question 3

What are the 3 most common types of phosphoglycerides?

Answer 3

1. Phosphatidyl-choline (eukaryotes)
2. Phosphatidyl-ethanolamine (prokaryotes)
3. Phosphatidyl-serine

Question 4

Describe the structure of a phosphoglyceride.

Answer 4

Two fatty acid tails connected to a phosphate group by glycerol.

Question 5

Describe the structure of a sphingolipid.

Answer 5

One fatty group (not acid) connected to a phosphate group by sphingosine. Potential to add a fatty acid.

Question 6

What is the resulting structure called when another sphingosine is added to an existing sphingolipid?

Answer 6

Sphingomyelin.

Question 7

Describe the structure of a sterol.

Answer 7

Solid carbohydrate rings with small polar head group and non-polar hydrocarbon tail.

Question 8

How can cholesterol in a membrane be beneficial?

Answer 8

Can act as a temperature buffer by stabilizing the membrane at extremely high or low temperatures.

Question 9

Do prokaryotes have cholesterol? How do they protect against temperature fluctuations?

Answer 9

No, but they have other sterols which accomplish the same function.

Question 10

Describe the structure of a glycolipid. Where on the membrane are they localized?

Answer 10

One fatty chain and one fatty acid connected to a sugar by sphingosine. Always on the exterior of the membrane.

Question 11

How are archael lipids different from eukaryotic/prokaryotic lipids?

Answer 11

Archael: branched, ether-linked, monolayer

Pro-/Eukaryotes: unbranched, ester-linked, bilayer

Question 12

In human cells, how many different types of lipids are there (give a range)?

Answer 12

Between 500 and 2000 types.

Question 13

How does the ratio of saturated and unsaturated fatty acids in the bilayer change with temperature? What enzyme accomplishes the conversion?

Answer 13

Increased unsaturation in cold because of their looser association, keeping membrane fluid. Saturation/unsaturation done by enzyme desaturase.

Question 14

Why is asymmetry of the lipid bilayer important?

Answer 14

Critical for cell recognition, apoptosis signalling, membrane protein function, etc.

Question 15

What is the purpose of inositol phospholipids?

Answer 15

Involved in signalling pathways. They allow proteins to dock to the membrane.

Question 16

Do eukaryotic cells ever have lipid monolayers? In what capacity?

Answer 16

Yes. Monolayers are used in storage vesicles/micelles for hydrophobic molecules. Often associated with the ER.

Question 17

What 2 factors implicit to the association of proteins with the membrane affect protein function?

Answer 17

1. Method of association

2. Location on the membrane

Question 18

How are transmembrane proteins associated with the membrane?

Answer 18

They have a hydrophobic domain (or multiple) which crosses the membrane.

Question 19

What is the purpose of β-barrels in the membrane?

Answer 19

Act as pores/channels for molecules to cross.

Question 20

What are the 3 lipid anchors for lipid-anchored membrane proteins?

Answer 20

1. myristoyl anchor
2. palmitoyl anchor
3. farnesyl anchor

Question 21

What linkage allows a myristoyl anchor to bind a membrane protein? Is it reversible?

Answer 21

An amide linkage. Stable/irreversible.

Question 22

What linkage allows a palmitoyl anchor to bind a membrane protein? Is it reversible?

Answer 22

A thioester linkage. Reversible.

Question 23

What linkage allows a farnesyl anchor to bind a membrane protein? Is it reversible?

Answer 23

A thioether linkage (as in methionine). Stable/irreversible.

Question 24

What is a glycoprotein?

Answer 24

A membrane bound protein with an attached sugar on the extracellular side of the membrane.

Question 25

What differentiates the bound sugar of a proteoglycan from that of a glycoprotein?

Answer 25

Proteoglycan: long sugar with no branching, sugars added 1 at a time Glycoprotein: branched sugars added 14 at a time

Question 26

On which side of the membrane do integrated proteins have disulfide bonds? What about sulfhydryl groups?

Answer 26

Disulfide bonds = exterior | Sulfhydryl groups = interior

Question 27

How can protein mobility in the lipid membrane be restricted?

Answer 27

By tight junctions or because of functional limitation.

Question 28

How can proteins maintain their position in the membrane?

Answer 28

By forming complexes with anchored proteins, anchoring to cytoskeleton or extracellular matrix.

Question 29

What are some characteristics of a lipid raft?

Answer 29

- Higher than normal cholesterol - More GPI-anchored proteins - More sphingolipids - Slightly thicker membrane

Question 30

How can the shape of a membrane be controlled?

Answer 30

Through the integration of membrane-bending proteins which modify the bilayer to a desirable shape.

Question 31

How do small hydrophobic molecules move across membranes?

Answer 31

Diffusion.

Question 32

How do inorganic ions and small organic polar molecules move across membranes?

Answer 32

Transporters/Channels.

Question 33

How do large macromolecules move across membranes?

Answer 33

Endo-/exocytosis.

Question 34

What are the 2 types of passive transport?

Answer 34

1. Channel-mediated | 2. Transporter-mediated

Question 35

What differentiates the kinetics of a transporter from the kinetics of a channel?

Answer 35

Transporter: has a max saturation (transport rate) Channel: no max saturation (transport rate)

Question 36

What are the 3 types of active transporters?

Answer 36

1. Coupled transporters 2. ATP-driven pump 3. Light-driven pump

Question 37

What differentiates a symporter from an antiporter?

Answer 37

Symporter: 2 molecules are moved together in the same direction Antiporter: 2 molecules move in opposite directions for transport

Question 38

What are the 3 types of ATP-driven pumps?

Answer 38

1. P-type pump 2. ABC transporter 3. V-type pump / F-type ATP synthase

Question 39

How are the functions of a V-type pump and an F-type ATP synthase linked?

Answer 39

V-type: uses ATP to move protons out of the cell | F-type: moves protons into the cell to produce ATP

Question 40

What is required for a P-type ATPase to function?

Answer 40

ATP must be used to facilitate (anti)transport of molecules.

Question 41

How do ABC transporters work?

Answer 41

Use 2 ATP to move solute molecules into/out of the cell.

Question 42

What does the ABC in ABC transporter stand for?

Answer 42

ATP-binding casette.

Question 43

How do prokaryotes use ABC transporters differently than eukaryotes?

Answer 43

Prokaryotes: for import and export Eukaryotes: mainly for export

Question 44

What are the 4 main characteristics of ion channels?

Answer 44

1. Always passive 2. Have high ion selectivity 3. Super high efficiency 4. Gated (open or closed)

Question 45

What are the 4 types of ion channels?

Answer 45

1. Voltage-gated 2. Ligand-gated (extracellular ligand) 3. Ligand-gated (intracellular ligand) 4. Mechanically gated

Question 46

How is the membrane potential in animal cells created?

Answer 46

Through the movement of Na+ and K+ ions across the membrane through diffusion or transport.

Question 47

How many of ions are moved across the membrane by an Na+/K+ exhanger per molecule of ATP?

Answer 47

3 Na+ out, 2K+ in.

Question 48

K+ diffuses via K+ leak channel according to chemical gradient until _______.

Answer 48

Membrane potential approaches 0 (never reaches neutral charge though).

Question 49

How is the K+ channel impermeable to Na+?

Answer 49

The K+ leak channel has a selectivity filter made up of carbonyl oxygens which can interact with the K+ ion (after hydrate shell lost) but not the Na+ ion.

Question 50

How come the Na+ ion channel is impermeable to K+ even though it is larger than the K+ channel?

Answer 50

The channel is large enough to allow the passage of Na+ with its hydrate shell but too small to allow passage of hydrated K+. Loss of K+ shell would be unfavourable though.

Question 51

What do aquaporins transport? What do they not transport?

Answer 51

Only water. Nothing else.

Question 52

How do aquaporins remain impermeable to ions?

Answer 52

Small enough that they only allow H20 to pass one at a time.

Question 53

How do aquaporins remain impermeable to protons?

Answer 53

Because of a double Asn region which breaks up the H20 chain (which would otherwise relay H+).

Question 54

Why do voltage-gated channels have lateral portals?

Answer 54

To allow the central cavity to be influenced by other factors (ex: hydrophobic drugs).

Question 55

What is the purpose of the inactivation gate on a voltage-gated channel?

Answer 55

Plugs the open state to facilitate membrane potential propagation (closes during refractory period).

Question 56

What differentiates patch current from aggregate current?

Answer 56

Patch: multiple small depolarizations Aggregate: sum of the patch currents

Question 57

In a transmitter-gated ion channel, what is the purpose of an excitatory neurotransmitter?

Answer 57

Opens cation channels, depolarizes.

Question 58

In a transmitter-gated ion channel, what is the purpose of an inhibitory neurotransmitter?

Answer 58

Opens K+ or Cl- channels, repolarizes.

Question 59

What is an example of a transmitter-gated ion channel?

Answer 59

Neuron synapses.

Question 60

What might be the purpose of drugs which target (neuro)transmitter-gated ion channels?

Answer 60

Muscle relaxants, anti-depressants, insomnia/anxiety/schizophrenia treatments.

Question 61

Organize the following by how easily they cross a membrane, from easiest to hardest: large polar molecules (glucose), small polar molecules (H₂O, urea), hydrophobic molecules (steroids, O₂), ions (Na⁺, Ca²⁺)

Answer 61

1. hydrophobic molecules (steroids, O₂) 2. small polar molecules (H₂O, urea) 3. large polar molecules (glucose) 4. ions (Na⁺, Ca²⁺)