Membrane structure Flashcards
What are the functions of the cell membrane?
Barrier that isolates the interior from the exterior. Selective permeability, cell signaling, endocytosis and exocytosis.
What is the general structure of a cell membrane?
The cell membrane consists of a phospholipid bilayer, that acts as a two-dimensional fluid, with proteins embedded.
What does it mean that the cell membrane is a two-dimensional fluid?
That each layer acts as a fluid with lateral diffusion of phospholipids readily switching places laterally. However vertical diffusion, also called “flip-flop”, happens very rearly and generally require a transporter.
What does it mean that a phospholipid is amphipathic?
Amphipathic means that it contains a hydrophobic and hydrophillic end. The phospholipid has a hydrophillic head with two hydrophobic tales.
What are the differences between a phospholipid molecule and a detergent molecule?
A detergent is a phospholipid with only one hydrocarbon tail as compared to two tails in a regular phospholipid molecule.
Describe the different methods that cells use to restrict proteins to specific regions of the plasma membrane.
A membrane domain is an area in the membrane in which some specific proteins are located and there is restricted transport of proteins in and out of the domain. To create such domains, cells can create tight junctions with other cells and thereby make a physical barrier preventing lateral diffusion across. Proteins can also be tethered to immobile structures such as the cell cortex or extracellular structures.
Can a membrane with many of it’s proteins restricted still be fluid?
The membrane can still be fluid, since only lateral diffusion is inhibited across the membrane domains but not necessarily within the membrane domain. Also the lipids can still move around the anchored proteins.
What determines the fluidity of a membrane?
Hydrocarbon tail length, the amount of saturated and unsaturated tails and the concentration of cholesterol in the membrane.
Longer tails, more saturated tails and higher concentration of cholesterol = More rigid membrane.
Shorter tails, more unsaturated tails and lower concentration of cholesterol = more fluid membrane.
Where does membrane assembly begins?
In the endoplasmatic reticulum (ER), where free fatty acids are used as substrates.
Which layer of the ER is phospholipids deposited?
Exclusively in the cytosolic half of the bilayer.
What is the function of the cell cortex?
It provides strength and supports to the membrane via a framework of proteins that connects to the cortex to transmembrane proteins.
Why is the cell cortex important for red blood cells, and how is it connected?
Transmembrane proteins are connected to a spectrin network in the cortex through attachment proteins. This linkage upholds their shape. Without the linkage to the cortex, the blood cells would have an abnormal structure and cause the individual to be anemic.
What are the different functions of membrane proteins?
They act as transporters and channels that selectively allow the transport of molecules and ions across the membrane. They act as receptors that can initiate intracellular pathways when an extracellular signal binds. They can function as anchor proteins. They can act as enzymes that catalyze reactions in the cytosol.
What are the different ways a membrane protein can associate with the lipid bilayer?
Transmembrane α-helices cross the membrane either once or multiple times, and β-barrels are made of several β-sheet that cross the membrane once. They can be a monolayer associated α-helix and only be anchored to the cytosolic half of the bilayer. They can be linked on either side of the bilayer by a covalent bond to lipid molecules. They can på protein attached, where they are connected by weak non covalent bonds to other membrane proteins.
Which of the membrane proteins are integral, and which are peripheral?
Transmembrane, monolayer-associated, and lipid-linked are integral. The protein attached is peripheral.
