The Cell Membrane Flashcards
What is the structure of the plasma membrane
a phospholipid bilayer (5-10 nm thick) with many phospholipids containing polar heads and non polar tails oriented side by side in layers. the polar heads are oriented out with the tails in the middle.
the plasma membrane is known to contain 4 things
- phospholipids
- cholesterol
- proteins
- carbohydrates
proportions of these elements vary between cell type
what are the parts of phospholipids?
they are amphipathic: polar hydrophilic head group and nonpolar hydrophobic tail group. One fatty acid tail usually has a cis-double bond and is kinked, this kink prevents close packing and allows membrane fluidity
the four most abundant phospholipids
- phosphatidylethanolamine
- phosphatidylserine
- phosphatidylcholine
- sphingomyelin
sphingosine
sphingosine is an important molecule for the membrane It forms sphingomyelin and can be phosphorylated to form a potent signaling lipid.
Where do you find each phospholipid in the bilayer?
Phosphatidylserine and Phosphatidylethanolamine are concentrated in the cytosolic monolayer (intracellular side). Phosphatidylcholine and Sphingomyelin are concentrated in the extracellular monolayer along with glycolipids.
What’s the deal with cholesterol?
cholesterol is a sterol molecule abundant in some membranes. It has a polar hydroxyl group which it orients close to polar heads of phospholipids. Cholesterol renders the bilayer less permeable to small, water-soluble molecules because it is rigid and hydrophobic.
Why do phospholipids have two fatty acid tails?
single tailed phospholipid molecules form spherical micelles rather than planar bilayers. double tailed phospholipids form planar bilayers.
what is a liposome?
liposomes are vesicles that spontaneously form when two-tailed phospholipids are mixed with aqueous solutions. it is energetically favorable to spontaneously form closed compartments instead of exposed planar edges
what is a black membrane?
a synthetic phospholipid bilayer formed across a small diameter opening separating two chambers filled with aqueous solutions. Black membranes allow us to study properties of membrane lipids and transport proteins. you can control what phospholipids are in the membrane in introduce specific proteins
three possible motions of phospholipids in a bilayer
- flexion
- lateral diffusion
- rotation
Thickness of a bilayer is determined by… and is important because…
thickness is determined by length of fatty acid tails and their degree of unsaturation (kinkiness). thickness in important because it determines which transmembrane proteins can insert into a particular bilayer
Lipid rafts
subdomains within the plasma membrane that act as hot spots for signal transduction. Sphingomyelin, Cholesterol, and specific membrane proteins involved in transmembrane signaling become concentrated. Sphingomyelin increases the thickness of lipid rafts, causing membrane proteins with long transmembrane domains to preferentially partition into lipid rafts.
how does signaling work across the plasma membrane?
There are many ways, but here’s a common example: an extracellular signal (like hormones) binds to the extracellular domain of a transmembrane protein which activates intracellular signaling proteins, triggering formation of intracellular signals that control cell activities
what is phosphatidylinositol?
a minor component of the plasma membrane, but very important in many cell signaling events,
