Membrane Structure Flashcards
What is the function of the plasma membrane?
Forms the boundary of the cell, and separates the cytosol from the extracellular environment.
What organelles have a membrane separating them from the cytosol?
Organelles in the endomembrane system: nucleus, ER, Golgi, mitochondria, chloroplast, lysosome, peroxisome
How thick is a phospholipid membrane?
about 5 nm thick
What percent of the mass of the membrane is attributed to lipids?
~50%
How many carbons are typically found in a fatty acid tail?
14-24
What are the three most common phosphoglycerides in membranes?
phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS)
Which main phosphoglyceride has a negative charge in the head?
phosphatidylserine (PS)
What are sphingolipids?
Phospholipids that use sphingosine rather than glycerol as a backbone, and contains a long fatty acid chain with a double carbon bond. At one end there is two hydroxyl groups and an amine group.
What is the most abundant sphingosine?
Sphingomyelin
What are glycolipids?
Like phospholipids but have sugar attached instead of a phosphate group.
Describe cholesterol
steroid with a 4-C ring structure attached to a polar hydroxyl group and a short nonpolar hydrocarbon chain.
How many times a second does a membrane component move laterally?
1 * 10^7 times per second
What kind of movement rarely happens in membranes
A flipping of phospholipids
What catalyzes the flip-flop between monolayers?
phospholipid translocators (AKA flippases)
What is different about the plasma membrane of bacteria cells?
They commonly only have one phospholipid and no cholesterol in their cell membrane.
A myelinated section of membrane would have greater or smaller glycolipid concentration?
Greater
What is a micelle?
aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid
Why are tears in membranes spontaneously fixed?
It is energetically favorable for the phospholipid bilayer to form a sealed compartment.
What properties will a membrane have if the fatty acid tails are shorter, with more doubly bonded carbons?
The phospholipids will be less tightly packed, resulting in a more fluid membrane with a lower transition temperature.
What is the function of the steroid rings of cholesterol?
To prevent the side chains of lipids from approaching each other, which prevents crystallization.
What are lipid rafts?
Microdomains of the plasma membrane with a higher concentration of cholesterol, sphingomyelin, and glycosphingolipids.
What is one theorized function of lipid rafts?
Cell signalling
Which phospholipids are found mainly in the outer monolayer?
phosphatidylcholine and sphingomyelin, both of which have a choline in the head group
Which phospholipids are found mainly in the inner monolayer?
Phosphatidylethanolamine and phosphatidylserine
On the cytosolic side of the plasma membrane, what does protein kinase C (PKC) need to bind to to become activated?
phosphatidylserine (PS)
What is the third main phospholipid found primarily on the cytosolic layer?
phosphatidylinositol (PI)
What does phosphatidylinositol (PI) result in?
phosphoinositide 3- kinase (PI3K), a signaling molecule
What happens to phosphatidylserine when a cell is undergoing apoptosis?
It will be translocated to the extracellular monolayer, which targets the cell for phagocytosis
Where are glycolipids found?
Extracellular monolayer of plasma membrane, and inner monolayer of organelles
Approximately how much is the protein concentration in myelin membranes?
25%
About how much is the protein concentration in the inner membranes of chloroplasts and mitochondria?
75%
What is the difference between an integral protein and a transmembrane protein?
an integral protein enters the plasma membrane but does not pass through the entire lipid bilayer
What are peripheral proteins?
Proteins attached to the plasma membrane but do not enter the lipid bilayer. They can be attached by covalently linked lipid chains.
What is a GPI?
composed of a phosphatidylinositol group linked through a carbohydrate-containing linker
What are membrane-associated proteins?
proteins that interact with other membrane proteins via noncovalent interactions
What characteristic, other than shape, determines a protein’s function?
Its location on the membrane
What are glycosylated membrane proteins?
proteins that have sugar moieties added to them.
what are the functions of the glycocalyx AKA sugar coat?
- Protects cell against mechanical and chemical insults
- Keeps unwanted cells away
- prevents unwanted cell-cell interactions
what is rotational diffusion?
a compound’s rotation on an axis perpendicular to the plane of the bilayer
what is lateral diffusion?
movements of compounds from side to side
Where are Major Histocompatibility Complex (MHC) molecules synthesized?
RER and Golgi
What is the function of MHC molecules?
To act as a “clear” tag, and also to be a marker for destruction when a cell is infected
