Dr. Guglielmo membrane properties (lec 9-10)

Question 1

What is Anemia? What are different causes of Anemia?

Answer 1

Lack of red blood cells or hemoglobin.
Caused by:
-blood loss
-decreased red blood cell production (iron deficiencies)
-increased destruction of red blood cells (hemolytic anemia)

Question 2

What is Hemochromatosis? What does it affect?

Answer 2

Iron overload (absorb 2-3x more iron than they need).
Affects liver, heart and endocrine organs.
*There are hereditary and non-hereditary forms - severe forms result from a hepcidin (comes from hepatocyte in liver) resistant ferroportin.

Question 3

How are lipids transported?

Answer 3

Absorption is not straight forward through our intestinal tract. Proper absorption requires emulsification (bile action). Transport in body requires transport vesicles.

Question 4

Describe the lipid transport post-absorption

Answer 4

-From the lacteals to the blood stream, lipids travel in chylomicrons throughout the body.
-Adipose cells can extract lipids (using lipoprotein lipases).
-Chylomicrons remnants are metabolized by the liver.
-Excess cholesterol and triglycerides can be stored by the liver.
-Liver can also send lipids to the rest of the body in water-soluble carriers -Adipose can send lipids to the liver in similar carriers.

Question 5

What are the components of chylomicrons?
What are chylomicrons?

Answer 5

Cholesterol, triglycerides and apolipoprotein.
Also contains phospholipids.
*Transport of lipids through lacteals and bloodstream.

Question 6

What are the types of lipoproteins and how do they differ?

Answer 6

1. Chylomicron - From intestine, lowest density, highest fat. Mostly triglyceride.
2. VLDL (very low density lipoprotein) - Made by the liver. Still mostly triglyceride, but less than chylomicrons.
3. LDL (low density lipoprotein) - Made by the liver. Mostly cholesterol, not very much triglyceride.
4. HDL (high density lipoprotein) - Returned to liver. Mostly protein
   *Lower density can float more (has more fat)
   *Want more HDL then LDL in bloodstream

Question 7

What is familial Hypercholesterolemia (FH)?

Answer 7

Genetic inheritance - severity dependent on # of mutant genes:
Heterozygote - 2x LDL in blood - develop cardiovascular disease
Homozygotes - 4-6x LDL in blood - heart attack in 20s
*These are mutations in the LDL receptor - doesn’t get taken up so it stays in the bloodstream.

Question 8

Describe the lipid bilayer and its characteristics

Answer 8

Dynamic structure composed of phospholipids.
-continuous replacement through recycling
-membranes contain lipids, protein, cholesterol, glycolipids and glycoproteins
-recycling between existing membranes (grows by inserting individual components like proteins and lipids)
-compositions vary

Question 9

What is the membrane composition of the liver? *percentages

Answer 9

Lipid = 52%
Protein = 44%
Carbohydrate = 4%

Question 10

What is the membrane composition of the Erythrocyte? *percentages

Answer 10

Lipid = 43%
Protein = 49%
Carbohydrate = 8%
*average cell

Question 11

What is the membrane composition of the Myelin? *percentages

Answer 11

Lipid = 79%
Protein = 18%
Carbohydrate = 3%
*mostly lipids

Question 12

What is the membrane composition of the mitochondrial inner membrane? *percentages

Answer 12

Lipid = 24%
Protein = 76%
Carbohydrate = 0%
*mostly protein - no carb because into mito

Question 13

Describe the asymmetry of the lipid bilayer

Answer 13

Inner and outer leaflets have different lipids types. Provides curvatures of membranes - directs overall shape of cell or organelle.

Question 14

Name the different membrane lipids

Answer 14

Glycerolipids
Sphingolipids (+ Glycerosphingolipid)
Sterols
*More unsaturated = can cause greater curvature.

Question 15

Types of Glycerophospholipids

Answer 15

Phsphatdiyl + R group:
Inositol (PI) (net negative charge)
Serine (PS) (net negative charge)
Choline (PC) (neutral)
Ethanolamine (PE) (neutral)

Question 16

Describe the membrane composition

Answer 16

-Phosphatidylcholine is most common (35-75%)
-Substantial portion is negatively charged (~20%)
-As much cholesterol as phospholipd
-More saturated fatty acids in plasma membrane, more unsaturated in organelles (more curvature)

Question 17

What does the fluidity of the membrane depend on?

Answer 17

-Level of unsaturated (more solid): saturated (more fluid) fatty acids
-Proteins (used to think created more fluidity but with more experiments determined it may actually be slower)
-Cholesterol content affects membrane fluidity (too much = block fluidity, too little = too fluid)
-Temperature (warmer = more fluid)
-Less fluid domains called lipids rafts

Question 18

What is the structure of Glycerophospholipids?

Answer 18

Fatty acids found at carbon 1 and 2
Can vary:
-Length: 12-22 carbons, usually 16-18
-Degree of saturation (no double bonds -saturated- to 3 double bonds -unsaturated

Question 19

Name 4 fatty acids described in this course

Answer 19

Stearic acid, Oleic acid, Linoleic acid, and Linolenic acid

Question 20

How many carbons, and double bonds are found in stearic acid?

Answer 20

18 carbons
0 double bonds
Enriched in meats (stear)

Question 21

How many carbons, and double bonds are found in Oleic acid?

Answer 21

18 carbons
1 double bond @ position 9
Enriched in olive oil

Question 22

How many carbons, and double bonds are found in Linoleic acid?

Answer 22

18 carbons
2 double bonds @ positions 6 & 9
Omega 6 fatty acid

Question 23

How many carbons, and double bonds are found in Linolenic acid?

Answer 23

18 carbons
3 double bonds @ positions 3, 6, & 9

Question 24

Give specific examples of the asymmetry of the membrane

Answer 24

Glycolipids on outer membrane of PM
More PC (phosphatidylcholine) in outer membrane of PM
PS (serine) in the inner membrane of PM
PI (inositol) on endosomes

Question 25

Types of lipid transport within the cell

Answer 25

1. Lateral diffusion (moves within two dimensional lipid layer) - rapid
2. Vesicular transport (vesicles move things in and out) - rapid
3. Monomeric exchange (two phospholipids bumping into each other and exchange cholesterol between membrane - more rare
4. Transbilayer movement (if uncatalyzed very slow) - rare

Question 26

Types of transbilayer lipid movement (catalyzed)

Answer 26

Flippase (take glycerol phospholipids - often PS - and flips to inner leaflet from outer leaflet)
Floppase (opposite to flippase - transfer PC to outer leaflet)
Scramblase (ramdomly takes one from one side and flips to other side) - calcium dependent
*Flippase and floppase are ATP dependent
If cell is undergoing apoptosis don’t get action of first two, but scramblase still works (this can signal to immune system that cell is dying)

Question 27

What are the characteristics of phosphatidyserine, and its importance in terms of the membrane

Answer 27

-PS belongs in the inner membrane (changes in membrane asymmetry can lead to disease if done improperly)
-Exposure of PS on the outer leaflet is a recognition signal for apoptosis to proceed via the binding of macrophages
-Disease causing or caused by membrane asymmetry include sickle-cell anemia, thalassemia, kidney stones, malaria, and pre-eclampsia

Question 28

Describe membrane rafts (lipid rafts) and what it is composed of

Answer 28

More ordered and tightly (thicker) packed than surrounding bilayer - causes less movement
Small (10-200 nm)
Heterogeneous
Buoyant
Detergent resistant
Composed of: cholesterol, sphingolipids, phospholipids, and specialized proteins (caveolin, flotillin, etc.)

Question 29

What are the functions of membrane/ lipid rafts?

Answer 29

-Concentrate/ separate proteins within the plane of the bilayer (endocytosis)
-Compartmentalize cellular processes (pre cluster proteins together for signalling - can dampen or promote)
-Membrane traffic
-Organizing centers
*Can also effect membrane fluidity (lateral diffusion)

Question 30

What are the resident and non-resident proteins proteins found in membrane rafts?

Answer 30

Resident proteins:
Caveolin
Flotillin
GPI-anchored proteins (e.g. prion protein)
Non-resident signalling proteins (can move in and out - visiting):
Some G-proteins/ G protein coupled receptors
Non-receptor tyrosine kinases
etc

Question 31

What is the composition of membrane rafts?

Answer 31

-Increased cholesterol concentration (2x more than non-raft bilayer)
-Enriched in proteins containing Glysylphosphatidylinositol (GPI) anchors and longer transmembrane domains (can handle because membrane raft is thicker)
-Sphingolipids
-Phospholipids

Question 32

What kind of cell-cell connections are membrane raft associated?

Answer 32

Tight junctions and desmosomes

Question 33

What do Caveolin protein do in the membrane rafts?

Answer 33

Insert themselves into membrane to create caveolae. Very sticky, can drag other proteins into lipid rafts. The caveolin scaffold begins first, then it makes a cave known as Caveolae (similar to clathrin coated pits - but smaller.

Question 34

Describe Flotillin protein role in the membrane raft and why it is called Flotilling

Answer 34

Inserts into membrane - does not create cave, it is flat.
During isolation - seperate lipid raft from the rest of the membrane - centrifuge and lipid raft will seperate and float on top (identified a protein with it), called this protein flotillin because it floated to the top.

Question 35

What are Caveolae?

Answer 35

Membrane raft - small, flask-shaped invaginations of the plasma membrane enriched in caveolin.

Question 36

What are planar lipid rafts?

Answer 36

Membrane raft - found in neurons, enriched in flotillin.

Question 37

How do caveolin and flotillin help with signalling?

Answer 37

Caveolin and flotillin can recruit signaling proteins - bring all 4 components together: neurotransmitter, G-protein coupled receptor, G-protein, and effector molecule.
*Signalling can be promoted or dampened.

Question 38

What are disease processes related to membrane rafts?

Answer 38

-Alzheimer’s disease (platforms for production of amyloid-B - neurotoxic protein)
-Prion disease - Creutzfeldt-Jakob disease (normal prion protein - PrPc - is converted to abnormal proteins - PrPsc - when come in contact in lipid rafts - GPI anchor required - conformational change)

Question 39

What are some difficulties in terms of studying membrane rafts?

Answer 39

Main challenge: limited methods
-Difficult to study lipid rafts in intact cells
-Lipid rafts are too small to be resolved by light microscopy
-In order to examine rafts, need manipulation of cholesterol (have twice as much in rafts) - through sequestration or depletion or removal - this can disrupt or change the structure of the raft though