Lipid Membrane and Solute Transport Flashcards
1
Q
What are lipid bilayers used for? (2)
A
- Membrane organelles
- Cytoplasmic membrane
2
Q
What provides the unique features of the different plasma membranes in various organisms?
A
The plasma membrane can differ based on the organism, the cell type, and the organelles involved
3
Q
How are the levels of cholesterol in the plasma membrane? What about the rough ER?
A
Plasma membrane: high cholesterol
Rough ER: low cholesterol
4
Q
What do we mean by “asymmetry” of the lipid bilayers?
A
- The distribution of membrane phospholipids can either be more present in the inner or outer monolayer
- The difference is very important
5
Q
Where is phosphotidylinositol located in the cell membrane?
A
Inside of the membrane since they are involved in signal transduction
6
Q
Where is phosphotidylserine located in the cell membrane?
A
Located on the inside of the membrane, but sometimes is shifted to the ouside
7
Q
How can integral membrane proteins be separated?
A
- Using detergents
- Makes the hydrophobic portion of IMP soluble
8
Q
What do peripheral membrane proteins interact with?
A
- Linked to the lipid bilayer
- Linked with transmembrane proteins
- Linked through a carbohydrate (ex: Glycosylphosphatidylinositol)
9
Q
Differentiate the ordered and disordered states of the lipid bilayer.
A
Ordered state; membrane is crystalline; gel-like
Disordered state: membrane is very fluid
10
Q
Are cell membranes usually ordered or disordered?
A
- Neither, cells are always in between these two states
- Different cells will have different ideal fluidity ranges
11
Q
How does heat affect the cell membrane?
A
- Produces thermal motion of the side chains
- Gel to fluid transition
12
Q
How does temperature affect membrane flexibility?
A
If the temperature increases over 40oC, the lipid bilayer goes into the disordered state (increases thermal motion)
13
Q
What is the regular temperature range for membranes?
A
20-40oC
14
Q
How does saturation of the fatty acid chains affect membrane flexibility?
A
- They increase order
- The more fatty acids, the more likely you will be in a crystalline state
- Unsaturated fatty acids have a kind
- Saturated fatty acids pack better
15
Q
How does uniform length of the fatty acid chains affect membrane flexibility?
A
Increases order
16
Q
How does sterol content affect membrane flexibility?
A
- Affects both ways depending on the situation their in
- Can decrease order if the bilayer has all saturated FA since sterols induce gaps in the bilayer, which increases disorder
- Can increase order if the bilayer has all unsaturated fatty acids since sterols will fill in the gaps
17
Q
At higher temperatures, will the cells increase saturated FA or unsaturated FA in the membrane?
A
- Increase saturated FA
- Because they have to maintain homeostasis of fluidity
- High temp: disorder
- Saturated FA: order
18
Q
Differentiate lateral diffusion and transbilayer diffusion.
A
Lateral: within each leaflet; lipid molecules can flow freely
Transbilayer (Flip-Flop): one leaflet to another; difficult and extremely slow (if uncatalyzed)
19
Q
What is uncatalyzed lateral diffusion necessary for?
A
In order to change the shape of the cell, to move cells, for lipid signaling
20
Q
What are the three transmembrane transporters that allow transbilayer translocations?
A
- Flippase
- Floppase
- Scramblase
21
Q
What are flippases? Does it require ATP? If not, what does it use? Does it have directionality?
A
- Bring a lipid form the OUTER leaflet to the INNER leaflet
- Requires ATP
- Directionality
22
Q
What triggers apoptosis/phagocytosis? What can prevent this from happening? What is it necessary for?
A
- PE and PS on the outer leaflet will cause apoptosis and phagocytosis (necessary for clot formation)
- Flippases move PE and PS from outer leaflet to inner leaflet
- Apoptosis/Phagocytosis is prevented
23
Q
What are floppases? Does it require ATP? If not, what does it use? Does it have directionality?
A
- Bring a lipid from the INNER leaflet to the OUTER leaflet
- Requires ATP
- Directionality
24
Q
What are scramblases? Does it require ATP? If not, what does it use? Does it have directionality?
A
- Moves lipids in either direction, towards equilibrium
- Does not require ATP
- Uses calcium instead
- No directionality
25
Can proteins move freely across the leaflet in the lipid bilayer?
Yes, if they are not anchored
26
What are proteins often anchored to in the bilayer? What are they?
- Ankyrin and Spectrin
| - Cytoskeletal filaments in the cell
27
What happens if proteins in the bilayer are not anchored?
They will move
28
What happens if the composition on the outer leaflet has increased levels of sphingolipids and cholesterol?
- Increased rigidity
| - Everything in the rigid region moves together; they are called rafts since they drift together
29
What are caveolae?
Caveolae are a type of "raft" that form when caveola is concentrated in a region
30
How does a caveolae form? How does it change the plasma membrane?
- A caveolin will interact with 3 fatty acyl moieties
- Two caveolin will dimerize (6 fatty acyl moieties total)
- When they concentrate, they will form a curvature in the plasma membrane, forming a caveolae
31
How do caveolae affect integral proteins?
When caveolae are formed, integral proteins in the area are stuck
- Because of this, they also become a sort of raft
32
What are caveolae important for?
Signal localization and signal integration
33
What does the fusion of two membranes require?
- Triggering signal
- Membrane recognition of each other
- Close apposition
- Local disruption of the bilayer on both membranes
- Hemi-Fusion (one of the leaflets from each side fuses)
- Fusion Proteins
34
What is the fusion and defusion of lipid bilayers necessary for?
- Exocytosis (sent out of the cell)
- Endocytosis (taken into the cell)
- Fertilization (fusion of sperm and egg)
- Cell division (separation of two plasma membranes)
35
When does membrane fusion happen at the synapse?
When a neurotransmitter is transmitted into the synaptic cleft
36
Which proteins draw two membranes together during membrane fusion?
- v-SNARE (vesicle)
- t-SNARE (transmembrane)
- Recognize and bind to each other, zipping up and drawing the two membranes together
37
What does zipping up cause during membrane fusion? What does it lead to?
- Causes curvature on the cell membrane and on the vesicle
| - Favouring hemifusion between outer leaflets
38
What is hemifusion?
Inner leaflet of both membranes come into contact
39
What does complete fusion create? How are the vesicle contents released outside of the cell?
- Creates a fusion pore
| - Pore widens; vesicle contents are released
40
What is simple diffusion? What can pass through?
○ Non-polar, small, lipid soluble compounds
| ○ Travel down the concentration gradient (high to low)
41
What is facilitated diffusion?
Travel down the electrochemical gradient
42
What is primary active transport?
- Requires ATP
| - Travels AGAINST the electrochemical gradient
43
What is secondary active transport?
- Requires ATP
- Travels AGAINST the electrochemical gradient
- Movement of one solute provides the energy for the moving of another solute by a neighbouring transporter (or in the same complex)
44
What is an ion channel?
○ Travels down the electrochemical gradient
| ○ May be gated by a ligand or ion
45
Can polar molecules traverse the lipid bilayer?
No, they have to be hydrated to pass
46
What is the advantage of using a transporter in simple diffusion?
- Simple diffusion requires a lot of energy
- The transporters will lower the energy since it is the transporter that interacts with the lipid bilayer
- Increases the speed
47
What are the two types of transporters?
- Carriers
| - Channels
48
What are carrier transporters?
- Slow and saturable
- Physically interact with the solute they carry
- Include primary active transporters, passive transporters and secondary active transporters
49
What are channel transporters?
- Fast and not saturable
| - Energy and concentration gradient
50
What is a passive transporter?
- Does not use energy
| - Moves solutes down the concentration gradient (high to low)
51
Give an example of a passive transporter.
- Glucose Transporters
- Transporters have two conformational statuses (T1 and T2)
- T1: transporter is open to the outside; glucose binds
- T2: transporter closes to the outside and opens to the inside; glucose is released inside, will then revert back to T1
- Rate: 50 000 times faster than the uncatalyzed diffusion
52
How are glucose transporters regulated?
By the hormone insulin
53
How does insulin affect the GLUT 4 receptor?
1) Normally, GLUT4 is kept within the cell in membrane vesicles (not available to help glucose come in)
2) When the insulin receptor is activated, it will bring the vesicle to the cell membrane, GLUT4 will get exposed to the exterior and glucose will flow in
3) When the insulin concentration goes down, the glucose transporters are brought back into the cell by endocytosis, forming small vesicles (catalyzed by PKB)
54
What does the lack of signal transduction in insulin dependent glucose transporters lead to?
Diabetes mellitus
55
Where does facilitated passive transport of ions happen in the body?
- In red blood cells
- Carries oxygen from lungs to the tissues
- Carries CO2 from the tissues to the lungs
56
What happens to RBC at the tissue level?
- Outside the RBC: more CO2, which diffuses in
- CO2 needs to be transformed
- It becomes HCO3-
- HCO3- dissolves in the blood plasma WHILE Cl- enters in
57
What happens to RBC in the lungs?
- Outside the RBC: less CO2, which diffuses out
- HCO3- comes in (leading to H2O and CO2) WHILE Cl- goes out
- CO2 is excreted through respiration
58
What are the three types of ion passage?
- Uniport
- Symport
- Antiport
59
What is a uniport?
Moves one ion from one side to the other side
60
What is a symport?
Cotransport involves two solutes in the same direction
61
What is an antiport?
Cotransport in the opposite direction
62
What are the two stages of the P-Type ATPase?
E1-P and E2-P
63
What are the three domains in the P-type ATPase?
N: nucleotide binding domain
P: phosphorylated domain
A: actuator domain
64
Which domain allows the P-type ATPase to get phosphorylated?
The P domain
65
Explain the E1 conformation of the P-type ATPase.
- Opening is toward the cytoplasm
- Binding sites for 2 calcium ions
- N domain is NOT bound to ATP
66
What happens when calcium binds to the P-type ATPase?
ATP, and magnesium, are brought to the N domain
67
What happens when ATP binds in the P-type ATPase?
- Brings P and N closer
| - Phosphorylation of Aspartate-351 in the P domain
68
What does the phosphorylation of Aspartate-351 in the P domain in the P-type ATPase lead to?
- Phosphorylation leads to conformational changes
| - Releases Ca2+ to the lumen (outer)
69
What causes the release of ADP and magnesium in the P-type ATPase??
- A domain moves in and breaks the partnership between P and N
- Causes the release of ADP and magnesium
- P domain becomes dephosphorylated
- A domain is reset
70
What type of transport is the Na+/K+ pump that maintains resting membrane potential?
Cotransport (antiport) by P-Type ATPase
71
How does the Na+/K+ pump work?
- ATPase pump
- Not Ca2+ that binds
- Na+ (inside) binds, causes conformational change, is released to the outside
- K+ (outside) goes in through cotransport (antiport)
72
What maintains resting membrane potential?
Na+/K+ pump cotransport by P-type ATPase
73
In the F-type ATPase, which side transports ions? Which side catalyses ATP to ADP?
- Transmembrane portion: transports ions
| - Cytoplasmic side: catalysis of ATP to ADP
74
In the F-type ATPase, what happens if a proton goes in? What happens if a proton goes out?
In: ATP to ADP is catalyzed
Out: ADP to ATP is catalyzed
75
Which ATPase is present in the mitochondria of Eukaryotic cells?
F-type
76
How are solutes transported? Give examples of solutes.
- ABC transporters
| - Amino acids, peptides, proteins, metal ions, lipids, bile salts, and drugs
77
What does ABC transporter stand for?
ATP-binding cassette
78
What do ABC transporters do?
Transport ions and solutes from the extracellular space to the cytoplasm
79
The fluidity of the lipid bilayer will be increased by:
A) Decreasing number of unsaturated FA (opposite, no)
B) Decreasing the temperature (opposite, no)
C) Increasing sterol content (sterol does both depending on the situation, does not necessarily increase)
D) Increasing the length of the alkyl chains (uniformity of length that makes it less fluid, not precise enough to be correct)
E) Substituting 18:0 (stearic acid) by 18:2 (linoleic acid) (saturated with unsaturated FA will increase fluidity)
Substituting 18:0 (stearic acid) by 18:2 (linoleic acid) (saturated with unsaturated FA will increase fluidity)
80
Identify the molecules derived from cholesterol:
- Arachidonic acid
- Gangliosides
- Phosphatidylglycerol
- Prostaglandins
- Cortisol
Cortisol
81
What transporter class do flippases belong to?
P-Type ATPase
82
What transporter class do floppases belong to?
ABC transporters
83
What do scramblases use since they don't utilize ATP?
Calcium
84
Are P-type or F-type ATPases reversible?
- P-type ATPase is not reversible
| - F-type ATPase IS reversible
