Membranes Flashcards
(106 cards)
1
Q
Separates cell from environment, regulates movement of materials into and out of the cell.
Why is it significant?
A
Plasma membrane
Gives cells their individuality. Allows for compartmentalization of intracellular organelles, roles, function. Like an adipose cell acts and reacts differently from a liver cell, from a cardiac cell, from a RBC, etc.
2
Q
Allows things, once they have been made to be post-translationally modified by things like glycoslyation (cleaving things off and putting things on), allows things to translocate, aka transport.
A
Golgi complexes processes
3
Q
Protein synthesizing machines in the cell.
A
Ribosomes
4
Q
Destroys peroxides
A
Peroxisomes.
If you dont get rid of peroxides like hydrogen peroxide, free radicals will be produced, which will damage dna lipids and proteins.
5
Q
Supports cell, aids in movement of organelles
A
Cytoskeleton
6
Q
Degrades intracellular debris.
A
Lysosome.
7
Q
Shuttles lipids and proteins between ER, Golgi, and plasma membrane.
A
Transport vesicle.
8
Q
Site of lipid synthesis and drug metabolism.
A
SER smooth endoplasmic reticulum
9
Q
Site that contains the genes (chromatin).
A
Nucleus
10
Q
Site of ribosomal RNA synthesis
A
Nucleolus
11
Q
Site of much protein synthesis
A
RER rough endoplasmic reticulum
Has ribosomes in here.
12
Q
Oxidizes fuels to produce atp.
A
Mitochondrion
13
Q
Segregates chromatin (dna = protein) from cytoplasm.
A
Nuclear envelope
14
Q
What is in between the inner and outer leaflet of the trilaminar membrane?
What is the approximate thickness of this membrane?
A
Intercellular space. (very hydrophobic because they are filled with hydrophobic tails).
50-one hundred angstroms.
15
Q
Give me examples of how membrane proteins can function for the cell (6).
A
- Transporters (atp)
- can act as enzymes (peripheral)
- signal transduction (receptors and signaling molecule)
- recognition proteins (allows us to differentiate self from non-self)
- fasten cells to adjacent cells
- attachment (attach proteins to different cells to distinguish between apical and basal ones)
16
Q
What are the 3 different types of artificial membranes?
A
Micelle
Bilayer
Vesicle
17
Q
Head group cross section is larger than the actual cross section of side chain. What type of interactions is it?
like attracts like, hydrophobic tails go inside, and the heads outside forming this structure.
A
Micelle
Non covalent interactions.
18
Q
Individual units are cylindrical (cross section of head equals that of the side chain).
Example phospholipid head group equal to that of the side chains.
A
Bilayer: has the head group, inter-membrane space, above it is outer leaflet, bottom is inner leaflet.
19
Q
Aggregations of numerous bilayers will form ?
What is the structure like?
What is the inside of the compartment called?
A
Vesicle. Basically a liposome (which mimics a cell). Liposome=vesicle.
Head group hydrophilic core, with surrounding hydrophobic middle made up of side chain tails, and then surrounded on the exterior by hydrophilic heads again.
Aqueous cavity.
20
Q
The total concentration of lipid required to form a stable micelle?
A
Critical Micellar Concentration.
Used often in labs to isolate proteins from lipid membranes. Like with like compete. Ex. Detergent effect
21
Q
What is the driving force of the formation of a phospholipid bilayer in an aqueous solution?
A
The hydrophobic interactions.
Driving force of membranes in our body.
22
Q
When I have one of the phospholipid monomers in water, because of the dipole nature of water, what is immediately going to happen?
A
The bulk solvent water is now going to line up to form a cage. This leads to a decrease in entropy (not what nature likes) because the waters are now highly ordered.
23
Q
When entropy decreases, what happens to delta G?
A
More negative.
Aka spontaneous
24
Q
Hydrophobic reactions are referred to as an increase in ENTROPY by a decrease in the Water.
What does increased entropy mean?
A
Means that it favors the formation of a bilayer and delta G is negative more spontaneous.
25
```
Phospholipid monomer in an aqueous environment.
Predicted H20 order?
Predicted entropy?
Predicted delta G?
Will a bilayer form?
```
High H20 order.
Decreased entropy.
Positive delta G.
No it will not form yet.
26
```
Phospholipids in an aqueous environment.
Predicted H20 order?
Predicted entropy?
Predicted delta G?
Will a bilayer form?
```
Low order because more of the water is in the bulk solvent.
Increased entropy
Negative delta G
Yes bilayer will form.
27
What type of interactions are necessary for the formation of the PL bilayers of molecules, but more specifically contributes to the overall membrane stability?
Non-covalent interactions.
examples of noncovalent bonds are: H bonds between neutral groups (like PE and water)/peptide bonds. Ionic interactions of attraction (ex is amino group of PE with the carboxyl group of aspartate)/repulsion (PE with another positive aa like lysine), hydrophobic interactions, or van der waals (any two atoms in close proximity).
28
This type of interaction is due to induced dipoles.
| What is the significant of having induced dipoles?
Van der waals
| Induced dipoles can help stabilize the membrane.
29
What is so special about the van der waal’s forces?
They help stabilize the membrane via induced dipoles.
So obviously the hydrophobic interactions are the major driving force for the formation of the bilayer. The fatty acid chains hate water that much that they flip around and form a liposome which has an inner aqueous membrane surrounded by a bilayer. (Outer leaflet, inter-membrane space, and inner leaflet). Then within that is the inner aqueous space.
30
Where is the inner aqueous space located and what is housed in it?
There is an outer leaflet, inter-membrane space, inner leaflet, then the inner aqueous space is within all that.
In biological membranes, the nucleus, mitochondria, peroxisomes, and all that is.
31
What kind of bond is between PE and h20?
hydrogen bond.
From the partial negative of the N on the PE and the partial positive of the H’s on the H20. The H bond is between the polar head group and water.
32
What kind of bond is between two PL head groups, PC and PS?
| And what type is it?
Ionic bond
Attraction.
What about PC and aspartate? (PL Head group and protein).
Same ionic and attraction?
Remember opposite charges attract, same charges repulse.
33
What kind of forces are between the fatty acid chains? (Of a liposome)
And what is the reason why they are there to begin with?
What do they do?
Van der waals.
They are there because of the induced dipoles.
They allow the close packing within the liposome, and will continue to do so until the electron orbitals overlap. Once they overlap they stop. The vanderwaal forces are weak but they are long because of the long carbon chains of the Fa’s. They essentially help Seal the membranes and prevent leakage, Even though they are weak. (Can be done in air, water, liposome etc).
34
What is the most stable artificial vesicle?
LIPOSOME
Because the membrane bilayers hydrophobic interactions like to pull on themselves to exclude water. And they have an aqueous environment inside too.
35
What are some of the advantages of an inner aqueous compartment/cavity?
In labs, can be used to deliver things to individuals or to transfect cells.
The liposomes are actually comprised of phospholipids , which the body sees an NORMal.
36
How can you use PL’s to deliver things to individuals?
Sonification. Gel filtration.
Well since the body sees liposomes as normal. We put phospholipids in beaker aqueous environment, and maybe have small aa’s like glycine, or different drugs of various genes. Then we sonificate it, basically using high frequencies of noise, and it causes the lipid to rise up, and now because of the hydrophobic interactions and noncovalent interactions, we get the formation of the liposomes. Within these liposomes we have the glycine trapped, which we can filter out, we can get a whole bunch of liposomes to contain what we want it to contain (drugs, dna, etc).
37
What is the significance of the liposome for drug delivery?
We can put a hydrophilic drug inside the aqueous cavity of a liposome which is surrounded by hydrophobic bilayers that can now enter places that it could not earlier because of it’s hydrophilic tendencies. We COULD also use hydrophobic drugs too, because we can store the hydrophobic lipid soluble drug within the hydrophobic bilayer of the liposome, or store both. You could also target it too.
38
Can you do targeting for liposomes?
Yes you can. You can make it go to where u want with targeting. Lets say someone has prostate cancer. and they were using a specific prostate antigen PSa. They will now put an antibody on that specific antigen that says, “go now to that particular cell, and once you get there to that cell, the antigen antibody will now bind to each other, cells fuse, and the drug will be delivered to the area of the body that you want it to be delivered. So basically, put drug in an environment that it likes within the liposome, put an antibody on it, target it, and tell it where to go.
39
Could integral proteins be enzymes?
Yes.
40
Could carbohydrates be added to proteins on a membrane?
Yes.
41
The ratio of lipids and protein within membranes is usually 1 for 1. Which exceptions are there?
Myelin in the neuronal regions (more lipid than protein). Because they are passive electrical insulators.
Inner mitochondrion more protein than lipid.
BUT OUTER mitochondrion is equal 1 for 1.
42
What are the 3 classes of lipids that membranes contain?
Phospholipids
Sphingolipids (glycolipids)
Cholesterol.
43
Which ratio is relatively equal?
Lipids/proteins in membranes
Or
Types of lipids within intracellular membranes
Lipids/proteins.
| the lipids within intracellular membranes varies .
44
What is the most predominant lipid within most intracellular membranes?
PC aka phosphatidylcholine.
| For most yes, but except for plasma membrane where it is least
45
What is the second most lipid composition within intracellular membranes?
PE
| Phosphatidylethanolamine.
46
Which intracellular membrane has the highest concentration of cholesterol?
Why is it useful?
Plasma membranes
Important for membrane fluidity.
In labs, if we want things to go to cells, and we dont want it to go too deep within the membrane, we can use Digitonin, it comes in pulls out cholesterol and pokes holes. If you play around with the concentration of digitonin enough you can actually get it to pull out the right amount of cholesterol and form holes, and the structure will still be intact, and wont impact any of the things in the inner membrane. So you can selectively get things into the cytosol by poking the cholesterol out.
47
What does cardiolipin do? What is it?
| Where is it found mostly?
So important in Stabilizing those proteins, cytochrome oxidase which is important in energy production.
Lipid. (Has 2 glycerol molecules on it)
Inner mitochondrial membrane.
48
What is cytochrome oxidase important for?
| Where is it found mostly?
Energy production.
| Obviously inner mitochondrion.
49
Where are sphingolipids enriched in?
| Why?
Lysosomal membranes.
| That just happens to be the place where they get degraded, so they kinda just hang out there.
50
Why role does phospholipid asymmetry on the plasma membrane play? (In regards to outer/inner monolayers)
What is the other role? Not as important but still.
Affects signaling, cell signaling, big role.
| Contributes to transmembrane potential.
51
Which are the choline containing lipids? (2)
| Where are they enriched?
PC phosphatidylcholine, and sphingomyelin.
| Enriched in the outer leaflet aka outer monolayer of the plasma membrane.
52
What are the negatively charged phospholipids? (5)
| Where are they enriched?
```
Phosphatidylserine PS
PhosphatidylLinositol Pl
PhosphatidylLinositol4phosphate Pl4
PhosphatidylLinositol 4,5 biphosphate Pl45
Phosphatidic acid.
Inner leaflet, inner monolayer.
```
53
Which phospholipids are enriched in the inner leaflet? (6).
```
PE
PS
Pl
Pl4phosphate
Pl4,5biphosphate
Phosphatidic acid
```
54
Tell me the charges of the transmembrane.
| Why is it that way?
Negatively charged inner leaflet because of PS which is in majority there and is (-).and + outer leaflet.
Usually the PC PE and sphingomyelin is outer which are mostly zwitterions or neutral (there are some PS outside too but not as much).
55
What are flippases, floppases, and scramblases?
Phospholipid translocators that catalyze the translocation of PL’s into or out of the inner (cytosolic leaflet) or outer leaflets.
FLIPPases and floppases are atp dependent (atp->adp+Pi).
Flip moves PE and PS from outer to inner cytosolic leaflet.
FLOP moves PL’s from cytosolic inner to outer leaflet.
SCRM moves PLs in either direction toward equilibrium, NO atp req.
56
Give me a method of how you can analyze the asymmetric distribution of PE. Where is is mostly located without testing?
Treat/coat cells with amino modifying reagents like FDNB (total inner and outer permeant) and TNBS (outer impermeant). Extract lipids with organic solvents in a glass beaker with solvent to separate lipids by TLC (thin layer chromatography), after allowing capillary action you can identify spots that are separated compounds. Do asymmetric analysis, both absorb at 400 nm, do HPLC analysis which is quantification of peaks. FDNB (higher peak) minus TNBS = total amt inner PE there is. Which will show that PE is mostly enriched in the inner cytosolic leaflet.
57
What is a glycolipid composed of?
| What type of linkage and where?
Sphingosine backbone, fatty acid, and another fatty acid on the sn2 via amide linkage (aka N-C) that is often saturated (linear no double bonds). And then on the sn3 is the X which determines which type of glycolipid it becomes it has to be a carbohydrate though. If not then itll be a sphingolipid. The carbhohydrate on the x is what determines the glucolipidity lol.
58
Where are choline containing lipids usually found?
| Give me an example of one?
Extracellularly, outside, outer leaflet.
| Sphingomyelin, which is a sphingolipid with phosphidylcholine as the X.
59
Give me an example of a negatively charged carbohydrate.
Neuraminic acid
60
What is a cerebroside?
It is a glycolipid which is a sphigolipid, that has a glucose or galatose, aka sugar on its X. glycolipids usually have shingosine backbone, fatty acid on sn2 via amide linkage.
Glucose on the x makes it. Glucoxylcerebroside.
Galactose it will be galactoxylcerebroside.
61
What if you have more than 1 carbohydrate on the x of a sphingolipid?
You get a glycolipid known as GLOBOSIDE. Which can be di, tri, or tetrasaccharide on the X. Example is like lactoxyloramide.
62
What if you have more than 1 carbohydrate on the x of a sphingolipid with the addition of neuraminic acid?
What is neuraminic acid?
It will be called gangliosides GM2 which is a sphingolipid with a complex oligosaccharide on the X (more than 1 carbohydrate with neuramic acid ).
A negatively charged carbohydrate.
63
Where are cerebrosides, gangliosides, and globosides usually found? What class are they?
Mostly found on the extracellular outer leaflets.
| They are glycolipids which are sphingolipids with carbohydrates on the X.
64
What are the 3 types of membrane proteins, and what type of interactions are they mostly associated with?
Integral, firmly associated in membrane can be removed by agents that interfere with HYDROPHOBIC interactions.
Peripherals associate with membranes via noncovalents like electrostatics, and H bonding.
Amphitropic can be either noncovalent or covalent attach to lipids, they hang out in the inner cytosol, undergo biological stimulation, translocate to membrane. Important because they can hang out around the membrane even when it gets crowded.
65
What type of amino acids would you find inside an integral protein? Why?
Valine, leucine, isoleucine
| Hydrophobic interactions firmly placed.
66
What type of amino acids would you find on the outer portion of the inner membranes? (3) Why?
Serine, aspartate, glutamate.
| Because they are charged and polar.
67
How to remove an integral protein?
| Be specific.
Amphipathic Detergent.
Amphipathic detergents only because it has to have a polar region and a hydrophobic region.
You want this because you wanna take the protein out the way it is and then you can solubilize it. Which is what we are talking about with the micelle with the critical micellar concentrations CMC.
68
How to remove peripheral proteins?
Compete with whatever noncovalent interactions optimally put it together to begin with.
1. Change pH: disrupts ionic interactions. +,-
2. Chelating agent: It pulls out the calcium. example peripheral proteins have negative charge so it is probably aspartate or glutamate, then in between them is Calcium which is often used as a bridge between the peripheral proteins that contain the negatively charged amino acids, and sandwich between the negatively charged phospholipid enriched inner leaflet.The chelating agent pulls out that calcium, which now exposes the negatively charged aspartate and a negatively charged PS which repulse/repel each other and the peripheral protein drops out.
3. Urea: competes with the hydrogen bonding, noncovalent
4. Carbonate: is negatively charged so will compete with the ionic interactions.
69
This type of protein does some type of biological regulation and then goes to the membrane inner leaflet and drops off.
Amphitropic protein.
70
This type of protein is linked via carbohydrate bridge to a lipid, which tends to be phosphatidylinositol. What is it, and what is so special about its structure?
GPI-linked protein.
The structure allows it to be tethered to the membrane because the membrane is fluid and can move around. Gives flexibility on the arm, and also mobility within the plane of the membrane.
71
Give me two ways to remove a GPI-linked protein
1. Detergent which disrupts the lipid interactions.
2. Phospholipase C, enzyme that can cleave off the head group (where carb + lipid is attached). This is a confusing protein because it could be classified as amphitropic or integral, so she wont really classify it.
72
What happens when you put an amphipathic detergent in water?
You form a micelle, if you know concentration we can get the critical micellar concentration.
73
What are triton x100 and sodium deoxycholate?
| What can they be used for?
Triton x100 is a nonionic hydrophobic detergent
Sodium deoxycholate is an ionic amphipathic detergent.
Used for the removal of integral proteins which require the presence of amphipathic detergent.
74
What can you ultimately find out by using IEa and ea?
Whether or not it is a transmembrane inner leaflet or extracellular domain.
75
How can you determine the transmembrane arrangement of membrane proteins? Which compounds do you use to react with the free amino groups on proteins?
```
Determine by using the compounds Ea ethylacetimidate or IEa isoethionylacetimidate.
Ea is permeant(labels both intra/extra cell domains), and iea is impermeant (labels only xtracell domains, bc it has - charged sulfur group so3-). Radiolabeled to see on film.
P1 = peripheral w/ inner leaflet
P2 = transmembrane potein with amino groups exposed intra/extra
P2=peripheral proteins only exposed extracellularly.
Isolate protien by using sodium diosulfate sDS, and then separate with SDS gel electrophoresis which will separate by molecular weight. Expose on film and radioactivity will show by autoradiography.
iea only labels p2+p3, P1 is inner so does not have any part of its protein exposed to the extracellular domain.
If on the gel shows similar bars between like p3, which is peripheral extrcellular domain, that means that the proteins there are only exposed exracellularly .
```
76
Which amino acids are found on the outside near the Amino terminus and why?
Polar Charged.ones like Ser Thr Asn glu asp
Glycolyslation external
(Ser and thr have those hydroxyl groups on the outside)
77
Which amino acids are found mostly along the outer leaflet of the membrane area?
Glu (-)
Arg (+)
Which make up the ionic interactions on the outside leaflet.
Thr with the hydroxyl group so we have H bonding.
As we get closer we get some hydrophilic amino acids, which react noncovalently and are in contact with the polar head groups.
78
Which amino acids are found within the transmembrane Domain?
| What type of secondary structure is found here?
Within the fatty acid tails. Within the transmembrane.
Are hydrophobic amino acids like val, phe, leu, ile, met.
Alpha helix.
Minimizes nature of hydrophilic peptide bond, hides it
79
Which lipid interactions within the transmembrane domain help seal it?
Van der waal.
| And helps maintain the conformation of the hydrocarbon core.
80
Which amino acids can we have the glycosylation of on the external end of the amino terminus? (3)
Ser
Thr
Asn (N-linked glycosylaton)
81
What is hydropathy index?
Basically it tells us how many times the protein transverses the membrane. By measuring the delta g of 7-20 protein residues, and looking at the relationship of the amino acid side chain going from the hydrophobic polar solvent to the aqueous environment like water.
Unlike to like (h20).
82
Exergonic in HI?
Negative delta g, favorable, charged/polar residue, gives off heat, going from dont like to like. Lipid to water.
83
Endergonic in HI?
Alipathic aromatic, positive delta G, going from water to lipid or like to unlike. From water to polar solvent (hydrophobic).
84
What if I told you there was 3 positive delta G’s on the HI? What does that mean to you?
Which amino acids would most likely be there?
What is the secondary structure?
That there are 3 transmembrane potentials
hydrophobic ones like val, lec, ile, met
Alpha helix which minimizes the nature of the hydrophilic peptide bond.
85
What happens when I put a carbohydrate on an asn?
Prevents it from folding.
86
What is the most common post-translational modification of proteins?
Where does it occur?
Where is it mostly found on?
Glycoslyation. Of proteins
Occurs on ER and golgi.
Found mostly on soluble proteins, ligands (TSH), receptors angiotensin II, cell adhesions (selectins), structural proteins (collagen), immunoglobulin, transport proteins (transferrrin)
87
What it when I add one or more oligosaccharides of varying complexity to bind to a protein?
What type of bond is it connecting the oligosaccharide to the protein?
Rigid or flexible?
Hydrophilic or hydrophobic?
Glycoprotein.
Covalent bond
Flexible and hydrophilic structures will mask hydrophobic stretches on proteins which greatly impacts the folding.
88
What is the special ability of the glycoproteins that have to do with its structure?
Since it is very flexible and hydrophilic, it could mask the hydrophobic stretches on the proteins which can greatly impact protein FOLDING, and the very hydrophilic clusters of carbohydrates can alter the POLaRITY, and SOLUBILITY of the proteins.
89
What happens when I link a glycoprotein like GalNac to a Ser or Thr?
What type of bond is this?
Where is a majority of this found? What is an example of it?
Well Ser and Thr have hydroxyl groups, so when you link them to glycoproteins, you get an O-linkage. Covalent bond.
O-linked mostly found intracellularly INNER. Collagen, RNa polymerase, transcription factors.
90
What happens when you link glcNac to asn?
What type of bond is this?
Where is a majority of these found?
You get N-linkage which is amide linkage from the N on asn with a carbohydrate like glcnac.
Covalent bond
N-linked found mainly EXTERNALLY OUTSIDE oligiosaccharide chains of glycoproteins.
91
Where is glycosylphosphatidylinositol anchors found mostly?
What are they?
Extracellularly.
The carbohydrate bridge between protein and phosphatidylinositol.
92
This structure has a phospholipid head connected with the linositol group, connected to a carbohydrate bridge (maybe mannose or something), which is connected to a protein.
This type of structure gives flexibility to the protein, allows the protein to be tethered, but mobile within the plane.
Glycosylphosphatidylinositol anchors. GPI-linked protein which is usually linositol.
The exoplasmic surface is tethered but mobile.
93
Term for the Temperature where most PL’s transition from a rigid to a fluid state.
Phase transition temperature.
From a solid rigid (not good) state Aka paracrystalline state 1to a fluid state. Low temp Tm to higher temp Tm. But not too high or else you will denature everything.
94
What is the melting temperature of our membrane dependent on?
Length of the fatty acids, and number of double bonds (saturation).
As you increase the number of carbons , it requires higher phase transition temp to melt it.
As you decrease # of double bonds, it requires higher phase transition temp.
95
Which one has the higher phase transition temp?
Monosaturated vs polyunsaturated?
20 carbon chain fatty acid vs 9 carbon chain fatty acid?
9 carbon monosaturated, vs 9 carbon unsaturated?
These have the higher phase transition temp, aka more temp req to move from rigid to fluid state.
Monounsaturated.
20 carbon chain fatty acid.
9 carbon monosaturated.
Because these are more rigid and tightly packed.
96
Which have a lower phase transition temp?
N-Tetradecanoate vs n-hexadecanoate?
N-Docosanote vs n-octadecanoate?
Cis-triangle9-octadecenoate vs n-octadecanote?
Tm is the temp from which things go rigid to fluid.
Based on # C’s on Fa’s. And double bonds.
N-tetradecanoate is lower, hexa is higher Tm
N-octadecanoate is lower and n-docosanote is higher Tm.
The triangle 9 means location of double bond therefore it is unsaturated, therefore fluid, therefore Cis-9-octadcenoate is lower Tm.
97
When you are below the Tm transition phase temp, what is the orientation of the fatty acids?
Tightly packed and rigid hydrocarbon chains.
98
What does cholesterol do in relation to membrane fluidity?
amphipathic nature, it broadens phase transition temp. Make the membrane fluidity less sensitive to fluctuations in temp.
It interferes with the tight rigid hydrocarbon packing during low transition phase temps by going in and pulling them apart with the polar head groups of PL’s, and that increases the fluidity of the membrane
During high temps, the membrane is fluid, so cholesterol uses its rigid steroid nucleus to immobilize and limit fluidity of the tails of the membrane.
99
How long does it take for an uncatalyzed PL to move across the transmembrane within itself in the hydrophobic regions?
In artificial ones relatively quickly, but in actuality, it takes many days t1/2. It is hard for the polar head group to move thru that hydrophobic environment. We need translocators. Flip out in, flop in out, and scrab both but atp independent.
100
Why are anion exchange proteins much slower with lateral diffusion within biological membranes compared to artificial ones?
Because they care tethered to the cytoskeleton.
101
Pallmitoyl group on internal cys
N-myristoyl on amino terminal Gly
Farnesyl (or geranylgeranyl) group on carboxyl terminal cys
What are these examples of?
Lipid linked membrane proteins
Palmitoyl group on Cis. Is Dynamic = reversible can come on and off.
N-myristoyl on amino terminal gly, permanent, once it gets myristolayted it is stuck there.
Geranylation is kinda a dynamic process.
So these are pretty fluid.
102
What are lipid rafts? And what is their significance?
Islands of lipid modified proteins stuck floating around because they are enriched in sphingolipids (rigid) and cholesterol (rigid during normal higher fluid Tm). They are advantageous because during signaling (cell), since they are stationary, they form signaling platforms on the surface known as caveola which help cell signaling.
103
How can I determine if something moves during a membrane?
Fluorescence recovery after photobleaching
104
How does fluorescence after photobleaching work?
1. Tag lipids/proteins w/ fluorescence marker (ex Protein B). Restin
2. Look in microscope and measure the INTENSITY (y graph).
3. Laser and photobleach (makes intensity DROP str8 down).
Wait for recovery to rise again.
4. The recovery period shows how many are mobile and how fast it is moving in the plane of the membrane.
105
Can fluorescence staining be used to see the formation of hybrid cells?
Yes. Just stain it, wait for time after fusion, and then look to see if the cells were mobile or it stayed the same.
106
Which ones are permeable? To the membrane
Small polar molecules (h20, ethanol)
Large polar molecules (glucose)
Gases (Co2 O2)
hydrophobic molecules (benzene)
Charged molecules (H+ Cl- Ca2+ Na+, amino acids)
Permeable: gases, hydrophobic, small polar molecules
(Co2, O2, benzene, H20, Ethanol).
Impermeable: Large polar molecules, charged molecules.
(Glucose, amino acids, H+, Cl-, Ca2+, Na+)
