Dr. Guglielmo membrane properties (lec 9-10) Flashcards
What is Anemia? What are different causes of Anemia?
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)
What is Hemochromatosis? What does it affect?
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.
How are lipids transported?
Absorption is not straight forward through our intestinal tract. Proper absorption requires emulsification (bile action). Transport in body requires transport vesicles.
Describe the lipid transport post-absorption
-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.
What are the components of chylomicrons?
What are chylomicrons?
Cholesterol, triglycerides and apolipoprotein.
Also contains phospholipids.
*Transport of lipids through lacteals and bloodstream.
What are the types of lipoproteins and how do they differ?
- Chylomicron - From intestine, lowest density, highest fat. Mostly triglyceride.
- VLDL (very low density lipoprotein) - Made by the liver. Still mostly triglyceride, but less than chylomicrons.
- LDL (low density lipoprotein) - Made by the liver. Mostly cholesterol, not very much triglyceride.
- HDL (high density lipoprotein) - Returned to liver. Mostly protein
*Lower density can float more (has more fat)
*Want more HDL then LDL in bloodstream
What is familial Hypercholesterolemia (FH)?
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.
Describe the lipid bilayer and its characteristics
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
What is the membrane composition of the liver? *percentages
Lipid = 52%
Protein = 44%
Carbohydrate = 4%
What is the membrane composition of the Erythrocyte? *percentages
Lipid = 43%
Protein = 49%
Carbohydrate = 8%
*average cell
What is the membrane composition of the Myelin? *percentages
Lipid = 79%
Protein = 18%
Carbohydrate = 3%
*mostly lipids
What is the membrane composition of the mitochondrial inner membrane? *percentages
Lipid = 24%
Protein = 76%
Carbohydrate = 0%
*mostly protein - no carb because into mito
Describe the asymmetry of the lipid bilayer
Inner and outer leaflets have different lipids types. Provides curvatures of membranes - directs overall shape of cell or organelle.
Name the different membrane lipids
Glycerolipids
Sphingolipids (+ Glycerosphingolipid)
Sterols
*More unsaturated = can cause greater curvature.
Types of Glycerophospholipids
Phsphatdiyl + R group:
Inositol (PI) (net negative charge)
Serine (PS) (net negative charge)
Choline (PC) (neutral)
Ethanolamine (PE) (neutral)
Describe the membrane composition
-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)
What does the fluidity of the membrane depend on?
-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
What is the structure of Glycerophospholipids?
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
Name 4 fatty acids described in this course
Stearic acid, Oleic acid, Linoleic acid, and Linolenic acid
How many carbons, and double bonds are found in stearic acid?
18 carbons
0 double bonds
Enriched in meats (stear)
How many carbons, and double bonds are found in Oleic acid?
18 carbons
1 double bond @ position 9
Enriched in olive oil
How many carbons, and double bonds are found in Linoleic acid?
18 carbons
2 double bonds @ positions 6 & 9
Omega 6 fatty acid
How many carbons, and double bonds are found in Linolenic acid?
18 carbons
3 double bonds @ positions 3, 6, & 9
Give specific examples of the asymmetry of the membrane
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
Types of lipid transport within the cell
- Lateral diffusion (moves within two dimensional lipid layer) - rapid
- Vesicular transport (vesicles move things in and out) - rapid
- Monomeric exchange (two phospholipids bumping into each other and exchange cholesterol between membrane - more rare
- Transbilayer movement (if uncatalyzed very slow) - rare
Types of transbilayer lipid movement (catalyzed)
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)
What are the characteristics of phosphatidyserine, and its importance in terms of the membrane
-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
Describe membrane rafts (lipid rafts) and what it is composed of
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.)
What are the functions of membrane/ lipid rafts?
-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)
What are the resident and non-resident proteins proteins found in membrane rafts?
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
What is the composition of membrane rafts?
-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
What kind of cell-cell connections are membrane raft associated?
Tight junctions and desmosomes
What do Caveolin protein do in the membrane rafts?
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.
Describe Flotillin protein role in the membrane raft and why it is called Flotilling
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.
What are Caveolae?
Membrane raft - small, flask-shaped invaginations of the plasma membrane enriched in caveolin.
What are planar lipid rafts?
Membrane raft - found in neurons, enriched in flotillin.
How do caveolin and flotillin help with signalling?
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.
What are disease processes related to membrane rafts?
-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)
What are some difficulties in terms of studying membrane rafts?
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
