Cell Membranes Flashcards
The phospholipid bilayer is considered _____________, meaning it has both hydrophobic and hydrophilic parts
Amphiphilic (amphipathic)
What are some examples of hydrophobic molecules that easily cross the lipid bilayer?
O2
CO2
N2
Steroids
What are some examples of small, uncharged polar molecules that are able to cross the lipid bilayer?
H2O
Glycerol
Urea
Ethanol
Describe the most abundant type of membrane lipid
Phospholipids = most abundant
Hydrophilic head with phosphate group
Hydrophobic tails with fatty acids
Backbone made up of glycerophospholipids or sphingolipids
What 3 membrane lipids are classified as being a part of the OUTER sheet? i.e., facing the EC environment
Phosphatidylcholine
Sphingomyelin
Glycolipids
What 3 membrane lipids are classified as being part of the INNER sheet? i.e., facing the IC environment
Phosphatidylinositol
Phosphatidylserine
Phosphatidylethanolamine
Which of the following is almost exclusively found in the inner sheet of a lipid bilayer, and its presence in the outer sheet is a marker for cellular apoptosis?
A. Phosphatidylserine
B. Phosphatidylcholine
C. Phosphatidylethanolamine
D. Phosphatidylinositol
A. Phosphatidylserine
What type of lipid found in the bilayer is considered similar to sphingolipids because it contains a sphingosine backbone, but contains a carb moiety rather than a phosphate group, and is only found in the OUTER sheet of the bilayer?
Glycolipids
Sphingomyelin consists of what 3 components?
LC fatty acid
Phosphocholine
Sphingosine
Niemann-Pick disease is characterized by a deficiency of what enzyme?
Sphingomyelinase
What type of lipid is classified as a steroid alcohol and is embedded within the bilayer with a hydroxyl head group and a sterol ring tail group?
Cholesterol
In Niemann-Pick disease, a deficiency in sphingomyelinase leads to accumulation of sphingomyelin in the ___________ of liver, spleen, CNS, and bone marrow leading to what characteristic symptoms?
Lysosomes;
Hepatosplenomegaly, mental retardation, seizures, ataxia, spasticity, “cherry red spot” in eye
____________ membrane proteins are embedded in the lipid bilayer and are stabilized by hydrophobic interactions. They are also likely to be _________, and act as transporters, ion channels, and receptors
Integral; polytopic
___________ membrane proteins are loosely bound via electrostatic interactions; one major example is cytochrome C
Peripheral
Lipid-anchored membrane proteins are tethered to the bilayer through a __________ bond
Covalent
____________ is a carbohydrate shell on the outer bilayer sheet that plays a multifunctional role
Glycocalyx
What are the 3 primary roles of the glycocalyx?
- Protection (from mech. injury)
- Adhesion (stabilizes cell-cell contact)
- Identification (i.e., blood typing via oligosaccharide composition)
What system in the body relies heavily on the glycocalyx for protection?
The vascular system relies on the glycocalyx as a physical barrier against leakage of fluid, proteins, and lipids across the vascular wall
It modulates adhesion of inflammatory cells and platelets to the endothelial surface
Damage is associated with increased cellular permeability and edema, resulting in increased adherance of leukocytes and platelets, which may be a risk factor for clotting/increased vascular vulnerability
RBCs have type-specific ABO and Rh ________ on their surface. __________ are present in the plasma, but whole blood is rarely given in transfusions
Antigens
Antibodies
Which blood type is considered the universal donor?
Type O [these individuals can only accept type O blood due to AB antibodies in their PLASMA]
Which blood type is considered the universal recipient?
AB, because they lack antibodies to either A or B antigens
If a mother gives birth to her second child and the child is diagnosed with hemolytic anemia, was her first child Rh+ or Rh-?
Rh+
The mother is likely Rh-, but was sensitized to the Rh factor in her first pregnancy, thus developing Rh antibodies which attacked the blood cells in her subsequent pregnancy (her second child is also likely to be Rh+)
A __________ is composed of a monolayer of amphipathic molecules, while a ___________ is a bilayer of amphipathic molecules.
Micelle; liposome
Compare micelles to liposomes in terms of structure
Micelle = monolayer
Liposomes = bilayer
Compare micelles to liposomes in terms of formation
Micelle = formed by surfactant molecules when dispersed in polar solvent
Liposome = formed by phospholipids; careful hydration of dry lipids with agitation
Compare micelles with liposomes in terms of size
Micelles = small
Liposomes = large
Compare micelles and liposomes in terms of what they transport
Micelles = transport hydrophobic molecules
Liposomes = transport hydrophobic molecules AND hydrophilic molecules
Compare micelles to liposomes in terms of their source
Micelles = biological (used to digest lipids by increasing access to lipases)
Liposomes = artificial (used for drug delivery)
What biological example of a micelle serves the main function of allowing digestion of dietary fats and oils?
Bile acids [these act as surfactants that emulsify fats + oils into micelles via colloidal suspension]
Proteins and lipids require rotation and lateral movement for function; the nature and composition of the bilayer imparts an inherent fluidity. What 3 factors primarily affect membrane fluidity?
Temperature
Lipid composition (saturated fatty acids impart rigidity)
Cholesterol (intercalating molecules decrease fluidity)
Unsaturated lipids and higher temperatures tend to __________ fluidity
Increase
An increase in temperature tends to __________ unsaturated lipids
Decrease
[this is a compensatory mechanism to maintain a certain degree of fluidity]
If a cell is in a stressful environment with a higher than normal temperature, would the cholesterol content of the lipid bilayer increase or decrease?
Increase - with the increase in temp, fluidity is increasing, so cholesterol will increase to fill any gaps being created and maintain a baseline fluidity
At colder temperatures, cells will _________ the amount of unsaturated lipids in the cell membrane, thus lowering the _____ and preventing transition to a rigid semicrystalline state
Increase
Tm
What 2 ways might a membrane become more fluid in terms of its fatty acid chains?
- Introduce points of unsaturation
2. Addition of methyl groups
True or false: flip-flop (transbilayer translocations) between the two sheets of a lipid bilayer does not readily occur, however some lipids DO flip between layers
True
___________ are protein translocators that are energy-dependent, unidirectional, and move lipids from OUTER to INNER sheet
Flippases
The outer sheet of the lipid bilayer is called the __________ leaflet while the inner sheet is called the ____________ leaflet
Exoplasmic; cytoplasmic
__________ are protein translocators that move lipids from INNER to OUTER sheet
Floppases
One class of flippases is called _________, which are energy-independent and bidirectional - meaning they facilitate lateral diffusion in a single membrane sheet
Scramblase
What clinical syndrome presents via defective platelet mechanism and blood coagulation due to prothrombin being cleaved to thrombin in the clotting cascade?
Scott Syndrome
The mechanism of action involved in the vascular injury associated with Scott Syndrome is due to a defective _________ to translocate ____ from the inner leaflet to outer leaflet.
___________ acts as a catalyst to induce the coagulation cascade, and binding sites for plasma protein complexes that convert prothrombin to thrombin.
Floppase; phosphatidylserine
Phosphatidylserine
What pathological condition is a type of hemolytic anemia that is associated with elevated cholesterol in erythrocyte membranes?
Spur cell anemia
In Spur Cell Anemia, elevated cholesterol in erythrocyte membranes decreases their fluidity. This leads to rigidity which causes the RBCs to lyse in the capillaries of the _________. SCA is also associated with beta-lipoproteinemia and advanced alcoholic _________.
Chronic liver disease impairs the metabolism of cholesterol by the liver, resulting in excess free cholesterol. Cholesterol binds the cell membrane, increasing the surface area, creating rough thorny projections called ______________
Spleen; cirrhosis
Acanthocystes
