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Lipids as signaling molecules Flashcards

1
Q

What is a hormone?

A

A chemical signal arising from a tissue. LONG distance travelled until reached receptor.

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2
Q

What is a paracrine?

A

It is a chemical message that travels shortly (produced in X tissue and affects X tissue). Ex. Eicosanoids

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3
Q

What is a autocrine?

A

A chemical message that is produced by a cell and the receptor is on this cell: response arises from this cell.

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4
Q

What is a juxtacrine? Ex.?

A

A chemical message that arises from a cell and travels a SHORT distance, since the receptor is on the NEXT cell nearby. Ex. Integrins

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5
Q

What is a pheromone?

A

A chemical message that travels from one organism to another, of the same species.

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6
Q

What are the 2 types of signaling molecules? Ex. of each?

A

Peptide (aa). Ex. Insulin

Lipids. Ex. Glycerolipids, prenols, sterols, sphingolipids, glycerophospholipids.

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7
Q

The lipid type of signaling molecules are classified in which 3 categories?

A

membrane lipids, storage lipids and bio(logically)active lipids.

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8
Q

Which 2 types of lipids act as intracellular signals?

A

Glycerophospholipids and sphingolipids.

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9
Q

What is important to know about Glycerophospholipids?

A

They are the precursors of inositol-phosphates (PIP2, IP3 and PIP3) depending on the enzyme that acts upon them.

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10
Q

In glycerophospholipids, what is the outcome that arises from phosphotylinositol 4,5-bisphosphate (PIP2) when PLC is the enzyme that acts on it? If it is PI-3K?

A

PIP2–(PLC)–IP3 + DAG

PIP2–(PI-3K)–PIP3

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11
Q

What are the 4 phospholipases that exist to cleave the lipid?

A 
Phospholipase A1 (at C1)
Phospholipase A2 (at C2)
Phospholipase C (at C3, between glycerol and phosphate gr)
Phospholipase D (at C3, between phosphate gr and head gr.)
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12
Q

The sphingolipids have ceramide; what is important about it?

A

Ceramide (Head gr with H only) stabilizes lipid rafts, which is important to localize signals on cell and for the dimerization of receptors.

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13
Q

What is the structure of a glycerophospholipid?

A

glycerol backbone, 2 FA chains, 1 phosphate gr with a head gr. (may be H)

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14
Q

What is the structure of a sphingolipid?

A

Sphingosine backbone, 1 FA chain, 1 head group (may be H)

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15
Q

In sphingolipids, what is a sphingomyelin?

A

Sphingolipid with phosphocholine (phosphate ge-CH2-CH2-N(CH3)3)

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16
Q

What is important to remember about eicosanoids?

A

It is an important molecule that arises from omega 3 or 6 and it is the basis to make other molecules. Glygosphingolipids use phospholipase A2 to yield Arachidonic acid (O6) to makes Prostaglandins, Thromboxanes and Leukotrienes. If a molecule outside this syst. acts upon one of the enzymes to make these 4 molecules, then 1 or all will be affected in some way.

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17
Q

In eicosanoids, prostaglandins have which functions?

A

They contract smooth muscles + regulate blood flow and body temperature.

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18
Q

In eicosanoids, thromboxanes have which functions?

A

form blood clots, thus lower blood flow

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19
Q

In eicosanoids, leukotrienes have which functions?

A

contract smooth muscles in lungs.

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20
Q

In eicosanoids, what enzyme is used to make prostaglandins from arachidonic acid? Thromboxane?

A

COX (cyclooxigenase enzyme). Same.

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21
Q

In eicosanoids, how does NSAIDS (aspirin and ibuprofen) affect prostaglandins and thromboxanes?

A

Since prostaglandins regulate body temperature (and thus, fever), we take aspirins to lower our fever, by blocking COX to make prostaglandins. But, since thromboxane also uses COX to be made, then its action is also stopped (not forming any blood clots)… NOTE: on the other hand, Omega 3 would only act on prostaglandins, not on thromboxanes.

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22
Q

In eicosanoids, if a person takes prednisone, how does it affect leukotriene? Thromboxane? Prostaglandins?

A

Leukotriene (lung smooth muscle contraction) will not be active, so the contraction will not occur, allowing people with asthma to breath. BUT, since prednisone inhibits phospholipase A2, then glycosphingolipids will not make arachidonic acids (thus no prostaglandin, no thromboxane, no leukotriene) ALL AT ONCE.

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23
Q

What do sterols act as? What type of receptor do they target?

A

Hormones. Nuclear receptors: They are produced by cholesterol and these sterols move throught the blood by carrier proteins until they reach a nuclear receptor.

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24
Q

What are some examples of sterols?

A

Testosterone, estradiol, cortisol, aldosterone.

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25
Q

Calcitriol is a good example of a hormone. Why?

Which nuclear receptor does it target?

A

Because vitamin D is responsible for the metabolism of Calcium (absorption + excretion + storage)
Vitamin D3 receptor.

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26
Q

Prenol is the sterol lipid signal of which 2 vitamins?

A

A and E (tocopherol)

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27
Q

What is prenol lipids 2 functions?

A

hormone and pigment.

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28
Q

How does prenol lipid function?

A

beta-carotene cleaves into 2 vitamin A (retinol), which gets oxidized into cis-Retinal and becomes trans-retinal when light hits it, which signals neurons to the brain.
ALso, when cis-retinal is formed, it can also be oxidized into retinoid acid, which is a hormone that signals growth in cells.

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29
Q

In prenol lipids, what is the difference in function of Retinol, Retinal and Retinoic acid?

A

Retinol (XXXXXXXX)
Retinal (vision)
Retinoic acid (growth of cells and reprod. syst. formation)

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30
Q

What is the nuclear receptors of prenol lipids?

A

Retinoid Acids Receptors (RAR) and Retinoic X Receptor (RXR)

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31
Q

What is another type of prenol lipid and is denoted as vitamin E?

A

Tocopherol

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32
Q

What is the overall function of a tocopherol?

A

Cofactor

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33
Q

What is vitamin E’s function?

A

Antioxidant (reacts with O2 radicals)

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34
Q

What is Vitamin K’s function?

A

Cofactor to prothrombin (blood-clotting prot.)

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35
Q

What is Warfrin’s function?

A

Inhibit prothrombin (blood does not clot)

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36
Q

In tocopherols, what is the difference between ubiquinone and plastoquinone?

A

Ubiquinone is in the mitochondria. (It carries e-)

Plastoquinone is in the chloroplast. (It also carriers e-).

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37
Q

What are the components of the Fluid Mosaic Model?

A

Lipids and non-lipid entities.
Glygolipids, oligosaccharide chains on glycoproteins, phospholipids, sterols, peripheral proteins (anchored with 1-3 FA OR with a polysaccharide chain), integral proteins, peripheral proteins (covalently linked to lipids)

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38
Q

The plasma membrane has different lipid composition dependng on…? (3)

A

Cell type (function)
Organelle
Organism

39
Q

Mostly, the inner leaflet has more of which lipid?

A

Phosphatidylinositol/serine. PInositol, since it is PIP2 and PIP3 in some pathways.

40
Q

Which 2 lipids are distributed on the outer monolayer of the plasma membrane?

A

Phosphatidylcholine and Shphingomyelin.

41
Q

The plasma membrane surrounds which parts of the cell?

A

The cell (duh!), the nucleus, the golgi, the mitochondria…

42
Q

Why is it important that phosphatidylserine be on the inner leaflet of the plasma membrane?

A

Since this molecule is associated to apoptosis, If it was on the outer layer, then this would signal the cell to die.
Inside, it’s function is to signal transduction too.

43
Q

How can integral proteins be removed from the plasma membrane?

A

Detergents: it makes the hydrophobic part of the protein soluble, because the detergent surrounds this hydrophobic domain.

44
Q

What is an example of a detergent?

A

Bile acids.

45
Q

How can peripheral proteins be removed from the plasma membrane?

A

By changing PH or using chelating agents or urea or carbonate; these will change the interaction (charge? denature bond?) the peripheral protein has with the membrane proteins or with the lipid bilayer.

46
Q

How can amphitropic proteins be removed from the plasma membrane?

A

Since they bind weakly (reversibly) to membrane lipids, and this process regulates their function, if a biological reaction comes along, it can either cleave the weak bond or solidify it. Proteins functioning in transduction of signals generated in cell membranes are commonly regulated by amphitropism. Ex. membrane affinity is controlled by modulation of the membrane lipid composition, and modification of the protein itself by ligand binding, phosphorylation, or acylation.

47
Q

Glycosylphosphatidylinositol is a glycolipid: lipid anchored in the membrane and the glyco part is in the cytosol, but they are linked. What can attache to this glycolipid?

A

A GPI - linked protein (Glycosylphosphatidylinositol), like Phosphatases.

48
Q

Which types of FA lead towards a paracrystalline state (gel/ordered)? Fluid state (disordered)?

A

Saturated, with same lengths.

Unsaturated, with diff. lengths.

49
Q

What are factors affecting flexibility (fluidity lvl) of membrane?

A
  • temperature (range between 20 to 40 degrees)
  • Saturation of FA chains
  • Same length of FA chains
  • Sterol presence (can go to fluid state (bottom) of to paracrystalline (top))
  • the cell’s regulation of FA content in membranes (ex. more sat. FA at high temp= fever.)
50
Q

What can phospholipids do easily as a movement within the cell membrane?

A

Lateral mvt.

It is super fast to occur, no need for catalizer.

51
Q

What CAN’T phospholipids do easily as a movement within the cell membrane? Why?

A 
Transbilayer diffusion (flip-flop/translocation).
It is so slow to occur when no catalizer is present.
52
Q

What can help the phospholipids flip flop within th cell membrane? (3)
What are their characteristics?

A

Flippase. ATP needed. Out to in.
Floppase. ATP needed. In to out.
Scramblase. Moves from both dir, same time. No ATP needed.

53
Q

What is specifically important about Flippase’s and phosphotidyserine? Phosphoetholamine?

A

Phosphotidylserine: it is normally on the inside, because the flippase keeps this lipid inside when it goes on the outer leaflet. If there was too much phosphotidylserine, then apoptosis is triggered (phagocytosis too!)
Phosphoetholamine (PE) is also important to stay in, because it is necessary for blood clot formation when on outer leaflet. We don’t want blood clot; if we do, then flippase action is stopped!

54
Q

Why is the cell’s regulation of FA content in membranes important?

A

It is to maintain homeostasis of each cell membrane (each membrane has a different characteristic fluidity)

55
Q

In the phospholipid bilayer, like lipids, proteins are freely mobile, but they have restricted movement due to spectrin, ankyrin, palmitoyl side chain and actin. How are they interconnected?

A

They are usually anchored! For example: Glycophorin and Chloride-bicarbonate exchanger of the erythrocyte have restricted motion.
The proteins span the membrane and are attached to SPECTRIN, a cytoskeletal protein, by another protein, ANKYRIN, limiting their lateral mobilities. Ankyrin is anchored in the membrane by a covalently bound PALMITOL SIDE CHAIN. Spectrin, a long, filamentous protein, is cross-linked at junctional complexes containing ACTIN. A network of cross-linked spectrin molecules attached to the cytoplasmic face of the plasma membrane stabilizes the membrane against deformation.

56
Q

What are lipid rafts?

A

Lipid rafts have 2 types of integral membrane prots:
1- anchored to the membrane by two long-chain saturated fatty acids (two palmitoyl groups or a palmitoyl and a myristoyl group) and
2- GPI-anchored proteins.

Lipid rafts are composed of sphingolipids (long and saturated) and cholesterol. The long, saturated SPHYNGOLIPIDS can form more compact and stable associations with CHOLESTEROL than can the shorter, often unsaturated, chains of phospholipids.
EVERYTHING IN THE REGION WHERE SPHINGOLIPIDS AND STEROLS ARE INCREASES RIGIDITY = EVERYTHING MOVES TOGETHER.

57
Q

What is Caveolin?

A

Protein located in one leaflet of the membrane and interacts w/ the phospholipids of the bilayer.
It is an integral membrane protein with two globular domains connected to the cytoplasmic leaflet of the plasma membrane. CALEOLIN BINDS CHOLESTEROL in the membrane, and the presence of caveolin FORCES ASSOCIATED LIPID BILAYER TO CURVE inward, forming caveolae (“little caves”) in the surface of the cell.

58
Q

What are caveolae?

A

It is a special type of raft: it INVOLVES BOTH LEAFLETS of the bilayer–The INNER leaflet, from which the CAVEOLIN domains is, and the OUTER leaflet, where typical SPHINGOLIPID/CHOLESTEROL raft with associated GPI-anchored proteins.

Used for TRANSDUCTION OF EXTERNAL SIGNALS INTO CELLULAR RESPONSES.
Ex. The receptors for insulin and other growth factors, and GTP-binding proteins and protein kinases associated with transmembrane signaling, are localized in the rafts

59
Q

What is the first step before caveolin can be functional and interact with phophoFA to form caveolae?

A

Dimerization

60
Q

Since whatever signaling protein is in the lipid raft (and gets stuck there), what 2 signal transduction features are affected?

A

Signal localization and integration

61
Q

What are examples of membrane fusions?

A

Exocytosis (out-in), endocytosis (in-out), viral infection, fusion of entities (sperm and egg), cell division.

62
Q

What are the requirements for 2 membranes to fuse?

A 
Triggering signal
Recognition of each other
Closeness
Local disruption of the bilayer
Hemi-fusion until total fusion of proteins.
63
Q

What is hemi-fusion?

A

It is when the 2 INNER leaflets of 2 membranes come close together but are not fused yet.

64
Q

An example of membrane fusion is neurotransmitters’s vesicles and the synapse. Explain how this occurs.

A

The vesicle is full of neurotransmitter. The vesicles comes close to the plasma membrane. The vesicle has v-SNARE and the plasma membrane, the t-SNARE. The v and t will recognize each other and bind, to zip the 2 membranes together. ZIPPING causes curvature and LATERAL TENSION on the bilayers = hemifusion! Hemifusion occurs, followed by TOTAL FUSION of the membranes, which forms a FUSION PORE. This widens and RELEASES the vesicle content into the synapse.

65
Q

What are the 6 types of solute transport across membranes?

A
  • Simple diffusion
  • Facilitated diffusion
  • Primary active transport (1 solute, ATP and against gradient)
  • Secondary active transort (2 solutes, no ATP, cause ion mvt in concentration gradient.)
  • Ion channel (gated by ligand or ion)
  • Inophopre-mediated ion transport (vesicle, down gradient)
66
Q

Why are transporters used instead of simple diffusion?

A

-To increase the speed of passage of the solute.
Simple diffusion uses a lot of E to diffuse molecule (physically make a passage and cross)= endogernic reaction.
Transporters are also endogernic reactions, but they use less Ea to diffuse solutes through a membrane = more efficient w/ E use

67
Q

What is the difference in reaction rate and degree of saturation of carriers vs channels?

A

Carriers – slow and saturable

Channels – fast and not saturable

68
Q

What is an example of a passive transporter?

A

Glucose transporter

69
Q

How does the glucose transporter (passive) make glucose pass through a membrane?

A

D-GLUCOSE out goes on GLUT1, where a pocket is SPECIFICally its shape. When the pocket closes on the D-glucose, then the long ‘bananas’’ of the carrier will open a space through the membrane and allow the glucose to leave the carrier into the inside.

70
Q

How many glucose transporters exist in the Human Genome?

A

12 (all in GLUT number format)

71
Q

How fast is the rate of the glucose transporter compared to the uncatalyzed diffusion?

A

50 000 x.

72
Q

Is the glucose transporter reversible?

A

Yes: in–out or Out–in.

73
Q

Where is GLUT1 in the body? GLUT2? GLUT3? GLUT4? GLUT5?

A

1: ubiquitous (EVERYWHERE)
2: liver, pancreatic islets, intestine
3: brain
4: muscle, fat, heart = activity increased with insulin
5: intestine, testis, kidney, sperm. = fructose transporter.

74
Q

GLUT 4 is increased with insulin (regulated by). Explain how the glucose transporter GLUT4 and insulin interact. (AKA insulin dependent glucose transporter)

A

As insulin levels rise, insulin receptor binds insulin; it makes the GLUCOSE TRANSPORTERS within the MEMBRANE VESICLES GO TO SURFACE and FUSE with the plasma membrane. There, the ‘open’ state of the glucose transporter is exposed to the outside of the cell, which ALLOWS GLUCOSE IN cell.
As the insulin levels drop, the GLUCOSE TRANSPORTERS are REMOVED BY ENDOCYTOSIS (‘unfuse’) in vesicles. These MANY VESICLES FUSE when in the middle of the cell to FORM AN ENDOSOME.
-Endosomes can break back into small vesicles for when insulin levels are high.

75
Q

What are endosomes?

A

A large vesicle (since small vesicles have fused together to form a huge one). They occur in insulin-dependant glucose transporter.
-Endosomes can break back into small vesicles for when insulin levels are high.

76
Q

How can we explain diabetes mellitus with the insulin dependant glucose transporters pathway?

A

The LACK OF SIGNAL TRANSDUCTION: absence of insulin to binds to the insulin receptor? Any problem during signal transduction (no vesicular mvt towards the membrane to abs. glucose?)

77
Q

What is an example of facilitated passive transport of ions?

A

The erythrocyte (RBC) with its CHLORIDE-BICARBONATE EXCHANGE PROTEINS.

78
Q

What are the steps for erythrocytes in respiring tissues, when using electroneutral co-transport (antiporter) of anions?

A
  • The CO2 diffuses into the RBC. Since CO2 cannot remain this way, it has to convert into HCO3-.
  • CO2 and H2O use carbonic anhydrase to yield HCO3- and H+.
  • HCO3- leaves the RBC through an antiporter (HCO3- going out to blood plasma and Cl- comes in RBC) = CHLORIDE-BICARBONATE EXCHANGE PROTEINS.
79
Q

What are the steps for erythrocytes in lungs, when using electroneutral co-transport (antiporter) of anions?

A
  • From blood plasma, HCO3- uses the Chloride-bicarbonate exchange prot. to go in the RBC, while Cl- is going out.
  • HCO3- uses carbonic anhydrase to go back to H2O and CO2.
  • CO2 diffuses out of the RBC to the lung.
80
Q

What are the 3 types of ion passage (transporters)?

A

Uniport, symport and antiport

81
Q

What are symport and antiport’s regrouped as (general)?

A

Cotransport

82
Q

In active transport, what is the difference between primary active transport and secondary active transport?

A

Primary: prot. uses ATP to pump NA+/H+ against concentration gradient.

Secondary: needs primary prot. to push Na+ against concentration gradient and then, secondary prot. will make the H+/Na+ to go WITH the concentration gradient, bringing another solute (Y) to go against its concentration gradient. aka used PMF.

83
Q

Is P-Type ATPase an active or passive transport?

A

Active

84
Q

How does the SERCA pump (P-type ATPase) work?

A

The ATPase is located between the ER lumen and the cytosol. It is composed of the M, A, P(phosphorylated domain) and N(nucleotide binding domain) subunits.
1- E1 = M transmembrane has the cavities for Ca+ to fit. The ATP binds to the N subunit as 2 Ca2+ fits in the M.
2- E1-P= N domains move towards the P and phosphorylates the Asp351 in the P domain (along with Mg2+). This creates conformational change to close binding site to either site and the Enz become E1-P
3- E2-P: Phosphorylation makes conformational changes makes Ca2+ leave outside. As A domain moves to release ADP.
4- E-2: P becomes dephosphorylated and Mg and Pi leave.
5- E-1: A domain resets and P and M too (thus changing the calcium entry (towards the out) now towards the in.

85
Q

In Active transporter, Na+ is usually the ion that powers the transportation of solutes. What are the 2 symport transporters (+ location) and the 2 antiport transporters (+ location in body)?

A

Symport: Na+-glucose
Na+- aa (intestinal epithelium cells)

Antiport: Na+-K+-ATPase
Na+-H+ pumps (kidney)

86
Q

What is Na+-K+-ATPase’s main function?

A

To maintain resting membrane potential/polarity

87
Q

What do P-type ATPases help the stomach achieve? How?

A

Parietal cells in the lining of the mammalian stomach have a P-type ATPase that pumps H +
and K + across the plasma membrane, thereby acidifying the stomach contents

88
Q

In the P-type ATPase, what are the 4 conformations it can be (+ its functionning)?

A

ATPase cycles between two forms:

  1. a phosphorylated form ( P-Enz II) with high affinity for K+ and low affinity for Na+ , and
  2. a dephosphorylated form (Enz I) with high affinity for Na + and low affinity for K+.

Functionning process:
1- Enz I = 3 Na+ go in enz. (entrance in cyt)
2- ATP phosphorylates Enz I and becomes P-Enz II (entrance in lumen)
3- P-Enz II releases Na+ in lumen and 2K+ bind to P-Enz II
4- Dephosphorylation of enz gives Enz I
5- Enz I releases 2K+ in cyt.

89
Q

Therefore, at resting membrane potential, what are the concentrations of Na+ and K+ in and out the the cell?

A

In: K+ high, Na+ low

Out: K+ low, Na+ high

90
Q

The SERCA pump acronym is?

A

Sarco/endoplasmic reticulum Calcium ATPase.

It’s a P-Type ATPase

91
Q

How does the F-Type ATPase work?

A

When 3H+ ions are pumped from out to in, ADP hits the ATPase to form ATP.
When ATP is hydrolyzed, 3H+ are pumped from in to out.

92
Q

The f-type ATPase is used in procaryotes, but is it in Eukaryotes too? Is it unidirectional or bidirectional?

A

Eukaryotic cells use this–mitochondria.

This is a bi-directional one (reversible)

93
Q

What are the possible solutes for ABC transporters?

A

aa, peptides, prots, metal ions, lipids, bile salts and drugs.

94
Q

How does the ABC transporter function is paired with a pump? With a channel?

A
  • If the ABC transporter is paired with a pump, the ATP is used to bring the solutes AGAINST their contentration gradient.
  • If the ABC transporter is paired with a channel, it uses ATP to open or close the channel.

Biochem... (6 decks)

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