A 1 year old girl was brought to the local clinic because of severe abdominal pain. She is pale skinned, shows marked mental retardation, and has an enlarged abdomen. After genetic testing the doctor diagnosed her with Niemann-Pick's disease. The symptoms of this disease are due to the accumuation of which one of the following lipids? A) Sphingomyelin B) Phosphatidylcholine C) Phosphatidylserine D) Cerebroside E) Ceramide
A medical student was studying the fluidity of the PM of hippocampal neurons. He cultured cells in the presence of a high concentration of fluorescently labeled PUFA's. Examination of the cells under a microscope showed bright fluorescence around the boundary of the cells suggesting that the PUFAs were incorporated into the neuronal membrane. Which of the following statements is the most accurate? A) The PM is likely rigid B) The PM is likely fluid C) The PM has high cholesterol D) The PM has phosphatidylserine facing the outside of the bilayer E) The PM has a 10-fold increase in integral membrane proteins
B) The PM is likely fluid
What 3 things make up a cell membrane?
Lipids, proteins and carbs - Arranged in asymmetric bilayer
Cell membranes are amphipathic, what does this mean?
They possess a hydrophobic tail and a hydrophilic head group
What are the most abundant lipids found in biological membranes?
What is a glycerophospholipid composed of?
Glycerol backbone, with a phosphate and 2 FAs esterified to backbone - Phosphatidylcholine, serine, and inositol
What is a sphingolipid composed of?
Sphingosine backbone, with a fatty acid and phosphorylcholine - Sphingomyelin - most common SL present in outer leaflet
What are glycolipids composed of?
Sphingosine backbone with carb (oligosaccharide residues)
Where are glycolipids found?
Outer leaflet of the lipid bilayer
What is cholesterol composed of?
Steroid nucleus with a hydroxy group and hydrocarbon side-chain. The latter interacts with the hydrophobic tails of membrane lipids
Where do plaques in Alzheimer's disease occur?
Lipid rafts - If you disrupt the rafts you cant get the plaques
Glycolipids, sphingomyelin and phosphatidylcholine are all found where in the PM?
Phosphatidylinositol, serine, and ethanolamine are all found where in the PM?
_____________ proteins are firmly embedded in the membrane and stabilized by hydrophobic interactions with lipids
Integral membrane proteins
___________ proteins are loosely bound to membrane through electrostatic interactions with lipids or proteins
_________________ proteins are tethered to membranes via covalent attachment to a lipid
Outer sheet of many membranes is covered with a carb shell called a ___________ due to presence of glycolipids and glycosylated proteins
What are teh 3 key functions of glycocalyx?
Protection, cell adhesion and cell identification - Disruption of the glycocalyx for example could lead to a leaky vessel wall
Where is phosphatidylserine found in healthy cells?
In the inner leaflet of bilayer
Dying cells are recognized by phosphatidylserine in the outer leaflet and are removed by ___________
Niemann-Pick disease is caused by a deficiency in activity of what?
Acid Sphingomyelinase (A-SMase
What is the role of Acid Sphingomyelinase (A-SMase)?
A lysosomal enzyme which breaks down sphingomyelin (SM)
What accumulates in Niemann-pick disease and where does it accumulate?
Sphingomyelin accumulates in lysosomes of the liver, spleen and CNS
What are the symptoms of Niemann-pick disease?
Enlargement of liver and spleen and neurological damage
An incompatible blood transfusion could result in what 3 conditions?
Acute hemolysis, renal failure, and shock
What blood type is the universal donor?
Type O because the RBCs have no blood group Ag but it does have Abs against A and B so it can only receive from O
What is the universal acceptor?
Type AB because the plasma does not contain any Abs, however they can only give to AB because they have A and B Ags
How is the D Ag inherited?
Do Rh+ individuals express the D Ag?
Yes -> Rh- do not
____________________ is a disease in which incompatibility between blood of mother and fetus
Erythroblastosis fetalis - When mom is Rh- and fetus is Rh+, the mom produces Abs that cross the placenta and can attack the baby
What is the structure of a Michelle?
- Monolayer of amphipathic molecules - Formed by surfactant molecules (detergents, emulsifiers) when they are dispersed in polar solvent beyond a critical miceller temp - Small
What is the structure of liposomes?
- Bilayer of amphipathic molecules arranged in 2 concentric circles - Formed by phospholipids (hydration of dry lips molecules in a non-polar solvent followed by mechanical agitation) - Large
What is the role of micelles
Used to transport hydrophobic molecules
What is the role of liposomes?
Can carry hydrophobic and hydrophilic molecules
Between micelles and liposomes which is biological and which is artificial?
Micelles are biological(bile salts/ bile acids -> used to digest lipids by increasing access to lipases) Liposomes are artificial (used for drug delivery)
What directions can proteins and lipids move in membranes?
Rotate and move laterally
Temp at which membranes switch from fluid to rigid state = _____________
Melting temp (TM)
Temp >>> Tm = ?
Temp > Tm = ?
Temp < Tm = ?
Do long FAs promote increased or decreased membrane fluidity?
Long = rigid Short = fluid
What is the role of cholesterol in a rigid versus fluid membranes?
Cholesterol in rigid membrane = increase fluidity Cholesterol in fluid membrane = decrease fluidity
When cells are exposed to low temps (
Unsaturated - This lowers the Tm and allows membrane to remain fluid at lower temps instead of transitioning to a rigid semi-crystalline state
Spur cell anemia is characterized by elevated levels of ___________ in RBC membrane
Cholesterol - Decreases fluidity and flexibility of membrane and causes RBCs to lyse as they pass through capillaries of the spleen
T/F: Membrane proteins and lipids can move from one leaflet of the bilayer to the other
False -> They cannot move leaflets!
What is the role of flippases
Move PE and PS from outer to cystolic leaflet
What type of ATP do flippases use?
What types of phospholipids do flippases move?
Phosphatidylethanolamine and serine - More specific for phosphatidyl serine
What is the role of floppase?
Moves phospholipids from cytosolic to outer leaflet
What type of ATP do floppases use?
What is floppase responsible for moving?
Phosphatidylcholine, sphingomyelin and cholesterol
What is the role of scramblase
Moves lipids in either direction, toward equilibrium
What type of ATP does scramblase use?
NONE -> scramblase doesnt use energy
Label 1 - 3
1) phospholipid bilayer
2) Phospholipid molecule
3) Hydrophilic heads
4) Hydrophobic tails
Label 7, 8, 10
7) Alpha helix protein (integral)
8) Peripheral protein